Download to read offline
![Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=tnzg20
Download by: [GNS Science] Date: 06 December 2015, At: 17:33
New Zealand Journal of Geology and Geophysics
ISSN: 0028-8306 (Print) 1175-8791 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzg20
Granitoids of the Dry Valleys area, southern
Victoria Land: Geochemistry and evolution along
the early Paleozoic Antarctic Craton margin
Andrew H. Allibone , Simon C. Cox & Robert. W. Smillie
To cite this article: Andrew H. Allibone , Simon C. Cox & Robert. W. Smillie (1993) Granitoids
of the Dry Valleys area, southern Victoria Land: Geochemistry and evolution along the early
Paleozoic Antarctic Craton margin, New Zealand Journal of Geology and Geophysics, 36:3,
299-316, DOI: 10.1080/00288306.1993.9514577
To link to this article: http://dx.doi.org/10.1080/00288306.1993.9514577
Published online: 23 Mar 2010.
Submit your article to this journal
Article views: 80
View related articles
Citing articles: 26 View citing articles](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-1-320.jpg)
![New Zealand Journal of Geologyand Geophysics,1993, Vol.36: 299-316
0028-8306/93/3603-0299 $2.50/0 © The Royal Society of New Zealand 1993
299
Granitoids ofthe Dry Valleys area, southern Victoria Land:
geochemistry and evolution along the early Paleozoic Antarctic Craton margin
ANDREW H. ALLIBONE
Department of Geology
James Cook University of North Queensland
Townsville, Q4811, Australia*
SIMON C. COX
ROBERT. W. SMILLIE
Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand
*Present address: Etheridge and Henley Geoscience
Consultants, P.O. Box 3778,Manuka, A.C.T 2603, Australia.
Abstract Field relationships and geochemistry indicate
granitoid plutons of the Dry Valleys area comprise at least
three petrogenetically distinct suites.The older Dry Valleys 1a
(DV1a) suite, comprising the Bonney, Catspaw, Denton,
Cavendish, and Wheeler Plutons and hornblende-biotite
orthogneisses, and Dry Valleys 1b (DV1b) suite, comprising
the Hedley, Valhalla, St Johns, Dun, Calkin, and Suess
Plutons,biotite granitoid dikes and biotite orthogneisses, were
emplaced before prominent swarms of Vanda mafic and felsic
dikes. Both the DV1a and DV1b suites are time transgressive,
with older intrusions in each suite being emplaced during the
later stages of deformation of the Koettlitz Group. Younger
granitoids that postdate the majority of the Vanda dikes
include: the Dry Valleys 2 (DV2) suite, comprising the Pearse
and Nibelungen Plutons plus several smaller, unnamed plugs;
and the Harker, Swinford, Orestes, and Brownworth Plutons
with identical field relationships and enclaves but distinct
chemistries.
Chemical characteristics and limited Rb-Sr isotopic dating
indicate plutonism before c. 500 Ma was dominated by the
Cordilleran I-type DV1a suite, inferred to have developed
during melting above a west-dipping subduction zone along
the Antarctic Craton margin. The chemical characteristics of
the DV1b suite indicate large-scale melting of a quartzo-
feldspathic protolith lacking residual plagioclase, but con-
taining refractory garnet. Potential DV1b suite source rocks
include metamorphosed immature sediments, possibly
underplated along the subduction zone associated with DV1a
magmatism, or older granitoid orthogneisses. Major DV1b
plutonism at 490 Ma marks the end of subduction-related
plutonism in southern Victoria Land. Younger DV2 alkali-
calcic, Caledonian I-type plutonism is inferred to have formed
in response to uplift and extension between 480 and 455 Ma.
G92027
Received 2 June 1992; accepted 29 April 1993
Lack of DV2 suite correlatives and Vanda mafic and felsic
dikes in northern Victoria Land suggests significantly
different tectonomagmatic histories along the early Paleozoic
Antarctic Craton margin.
Keywords geochemistry; granitoids; plutons; suites;
petrogenesis; southern Victoria Land; Antarctica; Dry Valleys
INTRODUCTION
Recently, Smillie (1992) proposed a two-fold suite sub-
division of granitoids in the Dry Valleys area of southern
Victoria Land, based on an integrated study of granitoid field
relationships and geochemistry in the Taylor Valley and Ferrar
Glacier area. The older Dry Valleys 1 (DV1) suite comprises
metaluminous, Cordilleran style, calc-alkaline I-type grani-
toids varying in composition from monzodiorite through
quartz-monzodiorite and granodiorite to granite. Granitoids
included in the DV1 suite by Smillie (1992) form two distinct
lithologic varieties: hornblende-biotite, commonly K-feldspar
megacrystic plutons; and equigranular biotite granitoids,
lacking hornblende. The relationship of these two varieties of
granitoid within the DV1 suite is unclear, and geochemistry
discussed by Smillie (1989) indicates that they cannot be
related by simple fractional crystallisation. The younger Dry
Valleys 2 (DV2) suite comprises metaluminous, Caledonian
style, alkali-calcic, I-type granitoids, the compositions of
which range from monzonite through quartz-monzonite to
granite. DV1 granitoids are generally enriched in TiO2,MgO,
CaO, V, Sc, and Cr and depleted in K2O, Rb, Pb, and Zr
relative to DV2 granitoids. Smillie (1992) inferred generation
of the DV1 suite during subduction along the Paleozoic
Antarctic Craton margin, and probable emplacement of the
DV2 suite during a later phase of extension, postdating
subduction.
Analysis of older orthogneisses intercalated with Koettlitz
Group metasediments (Cox & Allibone 1991) indicates that
the two distinct orthogneiss lithologic types (hornblende-
biotite and biotite only) are, with the exception of the Dun
Pluton, chemically identical to younger, relatively unde-
formed hornblende-biotite and biotite granitoids that make up
the DV1 suite. Consequently, emplacement of the DV1 suite
was inferred to span at least the later stages of Koettlitz Group
deformation (Cox 1993). Interrelated plutonism and deform-
ation during emplacement of the regional-scale Bonney
Pluton is discussed by Cox (1993). Garnet-bearing ortho-
gneisses intercalated with Koettlitz Group rocks south of the
study area (Skinner 1983; Findlay 1985) are not discussed
here, and their relationship to the granitoids of the Dry Valleys
area is currently unknown.
In Allibone et al. (1993a, this issue) we presented a map
and general description of the major plutons in the Dry Valleys
area, and a summary of the regional geology (see Fig. 1).An
intrusive history was derived from plutonic field relationships,
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-2-320.jpg)
![300 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
77.00
McMurdo
Sound -I
•
DV2 and DV2 ? plutons
SP = Swinford Pluton
Hybrid plutons
BP - Brownworth Pluton
Vanda mafic and felsic dikes
Packard Pluton, gabbro
DV1b undeformed plutons
DVIa undeformed plutons
CP = Cavendish Pluton
Gabbroic and dioritic orthogneiss
DV1b orthogneiss
DV1a orthogneiss
Koettlitz Group
Salmon Marble Formation
Hobbs Formation
Scale 10 km
Fig. 1 Inferred basement geology if overlying ice, sediments, moraine, and Ferrar Dolerite were removed to expose the Kukri Erosion
Surface. The DVIa and DVlb plutons (Bonney, Wheeler, Denton, St Johns, Valhalla, and Hedley Plutons) have a consistent northwest
orientation and are cut by northeast-striking younger dikes and the ovoid Pearse, Nibelungen, Brownworth, Orestes, Swinford, and Harker
Plutons.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-3-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 301
and this was correlated with new and earlier radiometric data.
Pluton mapping indicated that hornblende-biotite granitoids
(included in the DV1 suite of Smillie 1992) are generally
ellipsoidal, deep-level, concordant plutons, with northwest-
trending axes parallel to the belts of Koettlitz Group
metasediment. In contrast, equigranular biotite granitoids
(also included in the DV1 suite by Smillie 1992) are similarly
elongate in a northwest direction, but are generally younger
discordant plutons, which intruded by stoping at c. 490 Ma
ago. Swarms of northeast-trending Vanda mafic and felsic
porphyry dikes crosscut these hornblende-biotite and biotite
granitoid plutons. Most of the Vanda mafic and felsic dikes
were subsequently intruded by discordant ellipsoidal-shaped
plutons between 480 and 455 Ma. The occurrence of rare
Vanda mafic and felsic porphyry dikes cutting the younger
discordant plutons, and magmatic microgranitoid enclaves
resembling Vanda dike rocks within these plutons, indicates
emplacement of the Vanda dike swarms continued during and
after the emplacement of the discordant kilometre-scale
granitoid plutons.
This part of our study deals with the geochemistry of
plutons and the evolution of granitoids in southern Victoria
Land. Plutons mapped and described in Allibone et al. (1993a)
are shown in Fig. 1. New analyses of these plutons are
presented (Table 1), and their suite affinities examined.
Unravelling the relationship of hornblende-biotite and biotite
granitoids within the DV1 suite, and their relationship to the
Dun Pluton, is of particular interest. We test the applicability
of Smillie's (1992) DV1/DV2 suite subdivision to the new
plutons mapped and to a wider area of southern Victoria Land.
We outline problems associated with previous granitoid
subdivision schemes applied in southern Victoria Land, in an
attempt to relate our mapping to previous studies.
Similarities between the granitoid geology of the Dry
Valleys area and other parts of the Transantarctic Mountains
as far north as Terra Nova Bay have been inferred since the
early studies of Priestley (1914), Mawson (1916), and Smith
(1924). Subsequent mapping of Larsen Granodiorite (named
from Mt Larsen in northern Victoria Land) and Irizar Granite
(named from Cape Irizar immediately south of Terra Nova
Bay) in northern and southern Victoria Land, by Gunn &
Warren (1962), reinforced the earlier correlations of granitoid
rocks from throughout the Ross Sea sector of the Trans-
antarctic Mountains. The recent publication of major and trace
element analyses of granitoids in each of the terranes of
northern Victoria Land (e.g., Borg et al. 1987; Armienti et al.
1990),combined with the data included in this study, allows a
revision of these earlier correlations between granitoids of
northern and southern Victoria Land. Comparison of the
isotopic character of granitoids in the central Transantarctic
Mountains (Borg et al. 1990) and the Dry Valleys allows a
clarification of the correlation of granitoids and "basement
terranes" in these two areas. Reinterpreted dates (Allibone et
al. 1993a) are used to provide age constraints on the
geochemical, tectonic, and petrogenetic evolution of the
southern Victoria Land margin of the Antarctic Craton during
the early Paleozoic.
GRANITOID GEOCHEMISTRY
Analytical methods
Chemical analysis of granitoid samples was undertaken to
clarify relationships and the petrogenetic evolution of the
various plutons and granitoid dike swarms described in
Allibone et al. (1993a). X-ray fluorescence analyses were
carried out using Sc, Mo, and Au tubes in the University of
Otago Geology Department's Philips PW1410/20 AHP
Spectrometer. Samples were washed, then crushed in a
tungsten carbide swing mill. Major elements were determined
on fused disks using the method of Norrish & Hutton (1969).
Trace elements were determined on 5 g, 32 mm pressed
powder pellets using Mowiol (PVA) binder, and based on the
Norrish & Chappell (1977) procedures. Selected duplicate
samples were analysed by the analytical facility atJames Cook
University of North Queensland to confirm the accuracy of
results.
Analyses are listed in Table 1. In addition to our new
analyses, data from Palmer (1987, 1990), Allibone (1988),
Smillie (1989), Cox (1989), Ellery (1989), and Cox &
Allibone (1991) have been used in this paper. Data collected
for orthogneisses described in Cox & Allibone (1991) are
integrated with data from this and the above studies, requiring
a reinterpretation of orthogneiss petrogenesis.
Normative QAP compositions and DV1/DV2 suite
affinities
Plotting normative compositions of the various plutons and
dikes described in Allibone et al. (1993a) on the Streckeisen
(1976) QAP diagram defines two clear trends (Fig. 2). These
trends are synonymous with the calc-alkaline (DV1) and
alkali-calcic (DV2) suite trends described by Smillie (1992).
The Bonney, Cavendish, Denton, Wheeler, Catspaw, Hedley,
Valhalla, St Johns, Suess, Dun, Calkin, Orestes, and
Brownworth Plutons, various biotite granodiorite and granite
dikes, and hornblende-biotite and biotite orthogneisses plot
along the DV1 trend of Smillie (1992),ranging in composition
from monzodiorite to granite. The Pearse, Rhone, and
Nibelungen Plutons, unnamed quartz-monzonite dikes and
plugs, and all the Vanda felsic porphyry plugs and dikes plot
along the DV2 trend of Smillie (1992),ranging in composition
from monzonite to granite. The Pearse and Nibelungen
Plutons are the first kilometre-scale plutons identified as part
of the DV2 suite.
Several additional features are apparent. Biotite granitoids
(Hedley, Valhalla, Suess, and St Johns Plutons, and unnamed
biotite granite dikes and plugs—solid symbols on Fig. 2)
plotting in the DV1 field of Smillie (1992) form a tightly
constrained trend within the broader DV1 suite trend defined
by the hornblende-biotite granitoids (Bonney, Cavendish,
Denton, Wheeler, and Catspaw Plutons—open symbols on
Fig. 2). This apparent similarity in QAP composition is not
sufficient to confirm a petrogenetic relationship between the
two petrographically distinct granitoid types, within the DV1
suite of Smillie (1992).
The relatively young, discordant Swinford, Orestes,
Brownworth, Pearse, and Nibelungen Plutons, whose
emplacement postdates the majority of the Vanda mafic and
felsic porphyry dikes (Fig. 3), plot in both the DV1 and DV2
suite trends on Fig. 2, defined by Smillie (1992). This implies
the younger, discordant, granitoid plutons do not form a
geochemically coherent suite, despite their similar field
relationships, enclaves, and inferred pluton shapes. Instead, a
more complex petrogenesis is implied, with only the Pearse
and Nibelungen Plutons having field relationships and alkali-
calcic geochemistry analogous to the DV2 suite of Smillie
(1992). Analyses of the Harker Pluton indicate a highly
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-4-320.jpg)
![Table 1 XRF analyses of granitoids from the Dry Valleys region of southern Victoria Land. Sample numbers with prefix "P"refer to samples lodged in the petrology collection, Institute of Geological
& Nuclear Sciences, Lower Hutt, whereas those with prefix "O"refer to specimens in the University of Otago Geology Department's rock and mineral collection. Major elements are in weight %, trace
elements in ppm. n.d. = not determined, b.d. = below detection.
Sample
OU60757
OU60745
OU60746
OU60749
OU60750
OU60762
OU60763
P49935
OU60760
P49911
OU60752
OU60761
OU61128
OU61136
OU61135
OU61134
OU6H33
OU61118
VU30818
VU30823
VU30821
OU61037
P49933
P50185
P50190
P50161
P50184
OU60557
P49932
P49934
P49935
OU56854
OU56855
P49945
P49962
P49948
P49963
P49964
P49928
P49950
P49949
OU60478
OU60506
OU60509
OU60464
P50178
P50177
P5O18O
P50163
P50169
P50170
P50162
P50171
P50167
Long. E
162-15'
161-40'
161-52'
161-40'
161-42'
162-16'
162-16'
161-56'
162-14'
161-38'
161-44'
162-14'
162-26'
162-31'
162-29'
162-33'
162-40'
162-13'
161-39'
161-40'
161-45'
161°41'
162-01'
161-49'
161-48'
161-36'
161-40'
162-08'
162-03'
162-02'
161-56'
161-56'
162-16'
161-52'
161-37'
161-56'
161-46'
161-43'
161-22'
162-00'
162-00'
162-11'
162°15'
i62°ir
162-16'
161°31'
161-38'
161-15'
161-37'
161-40'
161-39'
161-37'
161-40'
161-39'
Lat. S
77-29.7'
77-31.3'
77-31.1'
77-31.3
77-31.3
77-31.5'
77-31.0'
77-46.9'
77-29.9
77-42.9'
77-31.3'
77-29.9
77-26.4'
77-29.2'
77°28.6'
77-29.0'
77-29.5'
77-27.3'
77-06.8'
77-09.3'
77-07.7'
77°43.4'
77°49.3'
77-42.3'
77-48.0'
77-42.0'
77-40.4'
77-48.0'
77-48.4'
77-49.5'
77°46.9'
77-03.9'
77-48.9'
77-33.4'
77-42.0'
77-33.8'
77-30.9'
77-31.0'
77-49.6'
77-33.6'
77-33.6'
77-42.6'
77-44.0'
77-44.6'
77-42.6'
77-46.0'
77-45.1'
77-45.1'
77-41.9'
77-42.2'
77-42.4'
77-42.0'
77-02.8'
77-41.8'
Pluton
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Denton
Denton
Denton
Denton
Denton
Denton
Wheeler
Wheeler
Wheeler
Catspaw
Catspaw
Catspaw
Catspaw
Catspaw
Catspaw
Hedley
Hedley
Hedley
Hedley
Hedley
Hedley
Valhalla
Valhalla
Valhalla
UBGSP
UBGSP
UBGSP
JBGSP
UBGSP
UBGSP
UBGSP
Felsic Porphyry
Felsic Porphyry
Felsic Porphyry
Felsic Porphyry
Felsic Porphyry
UQM, MSP
UQM, MSP
UQM, MSP
UQM, MSP
UQM, MSP
UQM, MSP
SiO2
57.36
62.65
62.88
63.31
63.89
64.38
64.73
65.70
67.34
68.35
70.05
72.56
60.53
64.31
64.73
64.93
70.96
71.38
57.01
63.41
66.13
71.02
71.44
72.31
72.33
72.56
72.78
68.17
70.13
70.40
70.50
71.48
73.58
71.45
71.48
73.58
71.89
72.05
73.71
74.82
75.37
75.55
75.97
64.02
66.47
70.58
71.11
71.74
59.50
60.57
60.73
60.74
63.01
67.83
TiO2
1.05
0.78
0.86
0.83
0.78
0.70
0.66
0.66
0.54
0.55
0.38
0.24
0.89
0.66
0.58
0.63
0.42
0.39
0.47
0.60
0.57
0.31
0.31
0 0
0.28
0.23
0.22
0.30
0.28
0.32
0.29
0.27
0.14
0.24
0.27
0.14
0.18
0.18
0.19
0.08
0.05
0.07
0.07
0.55
0.41
0.29
0.28
0.23
0.79
0.77
0.63
0.66
0.57
0.38
A12O3
19.81
15.93
16.47
16.44
16.14
16.55
16.96
15.83
15.95
14.95
14.76
14.23
17.06
15.13
16.79
16.62
15.40
14.04
19.83
16.76
15.92
14.42
14.29
14.01
13.78
13.96
13.66
16.49
15.59
15.38
15.46
15.41
14.58
14.67
15.41
14.58
15.40
15.45
14.54
13.66
13.46
13.34
13.13
16.17
15.68
14.08
14.14
14.13
17.96
17.58
17.84
17.93
16.93
15.71
Fe2O3T
6.80
5.45
6.27
5.59
5.13
4.99
4.41
4.42
3.76
3.48
2.98
1.68
6.39
5.83
4.45
4.56
2.79
2.63
4.28
4.92
4.51
2.43
2.40
2.07
2.52
2.12
2.37
2.39
1.95
2.18
2.01
2.24
1.32
2.03
2.24
1.32
1.44
1.39
1.38
1.04
0.79
1.15
0.41
5.03
4.02
2.40
2.47
2.31
5.71
5.69
5.23
5.69
4.85
3.30
Fe2O3
0.90
1.43
1.54
0.89
0.91
1.65
1.23
n.d.
0.74
n.d.
0.59
0.71
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.65
0.89
0.74
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.62
n.d.
n.d.
n.d.
0.82
0.18
n.d.
0.82
0.18
n.d.
n.d.
n.d.
n.d.
n.d.
0.21
0.10
0.88
1.18
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
FeO
5.31
3.62
4.26
4.23
3.80
3.01
2.86
n.d.
2.72
n.d.
2.15
0.87
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3.27
3.63
3.39
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
1.59
n.d.
n.d.
n.d.
1.28
1.03
n.d.
1.28
1.03
n.d.
n.d.
n.d.
n.d.
n.d.
0.85
0.28
3.73
2.56
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
MnO
0 0
0.08
0.09
0.08
0.08
0.06
0.06
00
0.00
0.06
0.05
0.00
0.10
0.10
0.05
ONOe
0.03
0.04
0.10
0.08
0.08
0.04
0.04
0.04
0.05
0.04
0.04
0.03
0.03
0.03
0.03
0.03
0.02
0.03
0.03
0.02
O^ON
ONON
0.03
0.03
0.02
0.04
0.00
0.09
0.07
0.04
0.04
0.04
0.08
0.08
0.09
0.09
oooo
0.06
MgO
2.16
1.84
1.98
1.96
1.65
2.17
1.47
1.56
1.11
1.37
0.88
0.42
2.25
1.94
1.55
1.30
0.79
0.78
2.76
1.79
1.33
0.48
0.49
0.28
0.51
0.32
0.33
0.56
0.46
0.50
0.47
0.48
0.26
0.40
0.48
0.26
0.26
0.27
0.27
0.08
0.04
0.17
0.11
1.24
0.69
0.39
0.34
0.37
1.27
1.21
0.99
0.98
0.90
0.61
CaO
5.65
4.31
4.59
4.32
4.07
4.19
4.46
3.76
3.40
3.26
2.77
1.90
4.87
3.78
3.81
3.84
2.61
2.51
8.14
4.11
3.66
1.83
1.84
1.45
1.71
1.69
1.44
2.95
2.42
2.44
2.34
2.35
1.84
2.41
2.35
1.84
2.04
2.09
1.60
1.21
1.05
1.20
1.46
3.53
2.46
1.71
1.64
1.54
3.83
3.68
3.29
3.35
2.99
2.22
Na2O
4.05
4.29
3.16
3.05
3.17
3.53
3.47
3.89
2.74
3.00
2.51
2.28
3.85
2.99
3.11
3.24
3.88
2.85
4.77
3.59
3.60
3.26
3.52
4.22
3.89
3.38
3.31
3.81
3.62
3.85
3.72
3.73
3.60
3.22
3.73
3.60
4.10
3.94
4.01
3.60
3.59
3.41
2.26
3.59
3.18
2.99
2.89
3.59
4.31
4.25
4.19
4.39
4.26
4.04
K2O
2.61
3.68
3.11
3.68
3.98
2.40
3.14
3.98
4.28
4.27
5.06
5.86
3.03
3.85
4.12
3.78
3.04
4.49
1.76
3.81
3.59
4.90
4.65
4.79
4.48
4.45
4.44
3.27
4.08
3.83
4.07
4.17
4.53
4.43
4.17
4.53
3.78
4.01
4.44
4.42
4.69
4.54
5.83
5.06
5.45
5.59
5.76
5.64
5.03
5.08
5.94
5.50
5.43
5.39
P2O5
0.24
0.27
0.21
0.19
0.19
0.23
0.22
0.15
0.14
0.13
0.09
0.06
0.22
0.16
0.16
0.16
0.10
0.10
0.24
0.18
0.15
0.06
0.07
0.04
0.07
0.04
0.04
0.06
0.06
0.06
0.07
0.06
0.04
0.04
0.06
0.04
0.03
ONON
0.02
0.01
0.00
0.02
0.01
0.22
0.13
0.06
0.06
0.06
0.22
0.20
0.17
0.17
0.15
0.09
LOI
1.03
1.17
0.91
0.99
1.11
1.39
0.74
0.62
0.74
1.14
0.76
0.52
0.37
0.85
0.53
0.51
0.32
0.23
0.96
1.00
0.88
0.52
0.63
0.54
0.50
0.65
0.60
0.68
0.67
1.21
0.80
0.54
0.57
0.59
0.54
0.57
0.51
^5O
0.48
0.35
0.35
0.47
0.54
1.04
1.25
0.87
0.67
1.01
0.95
0.41
0.39
0.43
0.41
0.63
Total
100.25
100.04
100.06
99.97
99.77
100.25
99.98
N00©O
99.74
100.60
100.05
99.66
99.57
99.62
99.89
99.63
100.30
99.46
99.96
99.85
100.04
99.27
99.66
99.97
100.10
99.44
99.24
98.53
99.28
100.20
99.76
100.62
100.37
98.88
100.62
100.37
99.66
99.94
100.70
99.31
99.40
99.87
99.76
100.12
99.53
98.99
99.41
100.70
99.63
99.53
99.49
99.93
99.58
100.30
Ga
30
24
26
21
22
21
19
N0
16
7
16
12
24
21
24
22
23
20
26
23
21
17
19
17
10
15
19
22
12
im
9
16
16
8
15
8
18
^5
15
15
8
19
11
19
19
15
15
18
18
18
16
16
20
16
Rb
124
140
120
156
184
105
100
139
119
138
184
118
154
135
163
123
92
136
101
150
147
180
184
157
185
158
141
95
114
151
111
133
133
121
124
144
134
131
117
173
121
214
147
268
378
257
260
240
132
152
145
131
157
177
Sr
587
479
443
483
422
434
499
485
563
417
469
512
496
437
442
481
542
382
808
420
390
291
2:2
174
210
198
185
674
578
557
653
409
408
445
363
347
631
576
422
344
445
162
546
536
367
261
254
235
896
794
816
716
584
476
Y
19
37
43
26
20
12
17
23
17
24
20
5
38
54
33
27
7
20
17
45
30
22
21
27
25
23
27
17
8
9
9
9
5
9
NI
10
12
7
8
12
9
13
b.d.
40
38
30
27
30
23
17
24
25
33
23
Zr
295
207
233
203
219
165
211
182
199
161
134
104
234
214
211
228
136
152
89
iwi
183
180
183
159
181
162
190
195
172
172
169
182
117
145
122
134
122
124
115
93
145
70
19
272
265
203
194
224
455
472
430
526
404
272
Pb
15
19
19
20
23
14
17
00
21
20
26
22
19
18
23
20
22
22
17
27
23
24
19
27
27
23
25
24
20
im
20
21
24
20
24
23
25
19
25
28
20
38
24
22
24
21
27
30
23
22
30
27
27
28
Th
17
24
17
23
22
13
9
iO
10
9
18
5
20
8
40
24
8
iV
5
iw
20
16
17
14
18
15
16
10
10
ni
7
10
7
6
6
7
b.d.
b.d.
b.d.
b.d.
6
12
b.d.
20
22
22
27
28
7
8
7
7
15
14
NC
8
6
6
6
6
10
6
6
6
5
5
4
9
10
7
6
7
6
b.d.
b.d.
b.d.
5
4
4
5
5
2
3
3
4
3
2
2
4
4
3
5
5
2
3
5
3
2
5
5
4
5
6
5
7
5
5
6
4
Cu
5
2
1
2
2
7
b.d.
2
4
5
b.d.
18
7
b.d.
b.d.
1
1
b.d.
b.d.
b.d.
b.d.
2
2
2
3
3
2
b.d.
3
4
2
b.d.
b.d.
2
1
2
4
3
3
6
2
b.d.
1
7
3
2
2
2
5
65
4
5
3
4
i n
102
72
86
78
75
83
70
67
61
60
44
27
88
87
78
66
60
45
67
77
73
56
46
53
59
84
58
49
43
48
43
39
30
52
42
38
35
^5
33
23
22
28
6
95
60
48
47
50
84
96
79
84
84
63
NP
25
16
18
14
15
18
14
iO
12
12
13
6
24
23
23
22
19
iV
9
iw
17
15
14
15
14
14
16
17
9
9
8
8
8
9
9
10
^O
9
8
13
12
11
b.d.
19
29
16
15
17
18
15
17
17
21
15
V
75
63
73
65
63
74
Mi
52
32
40
24
b.d.
80
64
49
44
27
27
86
57
40
15
18
11
17
13
11
b.d.
11
im
9
16
7
10
9
9
4
b.d.
5
b.d.
6
6
8
26
16
15
14
10
18
18
6
12
14
11
CN
16
12
14
•O
10
21
11
iO
b.d.
10
b.d.
b.d.
26
27
11
iN
9
8
27
iw
13
7
7
4
5
b.d.
4
b.d.
6
6
6
4
b.d.
5
b.d.
4
4
b.d.
4
4
b.d.
5
6
10
7
6
6
4
8
7
6
6
5
5
Ba
557
800
599
947
729
300
847
861
1646
1217
1380
1910
850
1041
935
1021
1152
656
335
807
786
835
794
580
638
513
625
1415
1247
1150
1183
209
903
1044
829
908
1098
1217
832
853
420
269
2135
804
630
658
596
556
2034
2107
2496
1684
1625
999
La
82
52
53
49
62
61
52
49
42
37
32
18
55
22
100
76
33
44
14
41
54
41
: 2
28
47
24
45
50
46
42
35
36
22
43
27
33
10
12
12
6
b.d.
10
6
63
63
65
69
68
61
51
59
74
83
77
Ce
148
102
11
103
126
107
103
95
92
86
81
60
115
57
191
136
60
87
25
76
93
97
93
76
102
67
101
97
104
96
93
61
34
94
78
81
56
62
57
45
34
19
b.d.
120
122
132
141
139
125
116
147
152
167
154
Pr
10
12
14
12
14
14
13
iO
8
10
9
7
13
8
19
iN
5
5
n.d.
n.d.
n.d.
7
8
9
10
8
10
n.d.
8
6
7
n.d.
n.d.
10
9
7
7
8
b.d.
b.d.
b.d.
n.d.
n.d.
n.d.
n.d.
13
13
17
13
6
10
18
17
15
NH
44
35
48
34
45
30
32
25
26
24
21
11
47
34
73
49
20
28
n.d.
n.d.
n.d.
28
22
23
31
15
30
27
19
im
15
n.d.
n.d.
23
14
19
b.d.
7
b.d.
b.d.
b.d.
b.d.
b.d.
44
48
46
44
48
42
b.d.
44
54
61
15
^
«t
S
o
oo
5"
1Q
1
f
5
|u>
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-5-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica
Fig. 2 Normative QAP composi-
tions of analyses of the various
plutons plotted after Streckeisen
(1976). Compositions of the DV1
and DV2 suites from Smillie
(1992) areplotted for comparison.
Granitoids mapped during this
study show an identical two-fold
subdivision into theDV1 andDV2
suites of Smillie (1992). Biotite
granitoids within the DV1 suite
(solid symbols) form a narrow,
well-defined trend within the
broader DV1 suite field of Smillie
(1992). Data are from this study,
Palmer (1987, 1990), and Ellery
(1989).
303
v i O N © " ^ •**•**—NO"^•**•** — N O m
I « » DC VI -H t—CT>l/l t^ © (N
© N o o w - i w - i u - i r - oot--©
r r - r - r N p r - v i m m m r j i n
© © © q o © o — © o © o
© © © © © d d © d o © ' ©
8SSS58SSSS3S
© © ' © d o d o © © © © ©
q q q q
c c c c
d d d d d d o d © © © ©
|^j ^ j ^ j r ^ pQ
OO n *—> — oo
§§iSS
Q60:AP40
quartz-monzonitel M quarU-monzodiorite
Tnonrartom6
A65:P35
X Marker Pluton
v Swinford Pluton
4- Pearse Pluton
O Brownworth Pluton
• Biotite granite dikes
M Quartz-monzonite sills
+ Felsic porphyry plugs
A35:P65 A10:P90
• Orestes Pluton
A Valhalla Pluton
T Hedley Pluton
• Suess Pluton
4 St. Johns Pluton
o Catspaw Pluton
A Denton Pluton
V Bonney Pluton
.,/2>Bonney Pluton (Smillie1992)
1 D V 1 s u i t e
(Smilli
e 1992)
O D V 2 suite (Smillie1992)
evolved composition, which plots at the intersection ofthe
DV1 andDV2 trends (Fig. 2).Further analysis is required to
define thesuite affinity ofthe Harker Pluton.
Relationship ofhornblende-biotite and biotite granitoids
within theDV1 suite ofSmillie (1992), and the"Dun
Type" orthogneiss ofCox &Allibone (1991)
In many ofthe discriminant and variation diagrams presented
below, hornblende-biotite granitoids of the DV1 suite
(hornblende-biotite orthogneisses, Bonney, Denton,
Cavendish, Wheeler, andCatspaw Plutons) display distinctly
different evolutionary trends from biotite granitoids ofthe
DV1 suite (Hedley, Valhalla, Suess, and St Johns Plutons,
biotite orthogneisses including theDunandCalkin Plutons,
and biotite granite dikes). This implies that theDV1 suite,as
defined by Smillie (1992), comprises two,petrogenetically
distinct suites. Thedistinct geochemistry of thehornblende-
biotite andbiotite granitoids previously included in the DV1
suite bySmillie (1992) isconsistent with the different styleof
emplacement of the major hornblende-biotite granitoid
plutons (Bonney, Denton, Cavendish, Wheeler) and biotite
granitoid plutons (Hedley, Valhalla, StJohns, Suess) outlined
in Allibone et al. (1993a). Accordingly, in the following
discussion, the hornblende-biotite granitoids are referred to as
DVla suite granitoids, andbiotite granitoids as DVlb suite
granitoids. TheDVla and DVlb suites are petrogenetically
distinct and unlikely to be derived from the same source
material. They are not subdivisions of a larger overallDV1
suite. DV1 is retained inthename of each suite to emphasise
the partly coeval, time transgressive nature of the DVla and
DVlb suites, inferred from field relationships outlined in
Allibone etal. (1993a) and illustrated inFig.3.
Harker variation diagrams (Fig. 4) indicate DVlb biotite
granitoids are enriched in A12O3, Na2O, and Sr relative to
DVla hornblende-biotite granitoids. Both types define
distinctly different trends on the variation diagrams. The
slopes of the A12O3 versus SiO2, Na2O versus SiO2 and Sr
versus SiO2 trends for the DVlb biotite granitoids are
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-6-320.jpg)
![304 New Zealand Journal of Geology and Geophysics, 1993,Vol. 36
migmatite development
—isoclinal folding
upright folding about
NNW trending axes
KOETTLITZ GROUP
hornblende-biotite
orthogneiss
. Bonney |
i Denton 1
Wheeler .,
Cavendish .
.Catspaw,
DRY VALLEYS 1a
(DV1a) SUITE
Dun
Calkin
biotlte orthogneiss
Medley
Valha
St.Johns
DRY VALLEYS 1b
(DV1b) SUITE
VANDA MAFIC DIKES
I Orestes .
Brownworth
STRONG DRY VALLEYS 2 CHARACTER
DRY VALLEYS 2
(DV2) SUITE
• qtz monzonite.
'dikes & plugs' Pearse
t Nibelungen
H
oldest
5 8 6 ' ' 4 9 0
AGE Ma NOT TOSCALE
486 I 477 I
youngest
Fig. 3 The inferred relative timing of emplacement of the various plutons,dike swarms,and granitoid suites mapped. Emplacement ofthe
DVla andDVlb suites overlaps withthe later stages of deformation and migmatitedevelopment inthe Koettlitz Group.Emplacement ofthe
DV2 suite postdates emplacement of the DVla and DVlb suites, and the majority of the VandaDikes.
especially steep relative to the DVla hornblende-biotite
granitoids. DVlb granitoids are also highly enriched in Ba
relative to DVla granitoids (Fig. 4), but values for biotite
orthogneisses show a wider scatter, possibly as a result of
incipient to extensive migmatite development. DVlb grani-
toids and orthogneisses are extremely depleted in Nb (not
plotted here) and Y, and Rb, K2O, MgO, Cr, V, and Th (not
plotted here) to a lesser extent, relative to DVla granitoids
(Fig. 4; Cox & Allibone 1991). Na2O/K2O ratios (Fig. 5) of
DVlb granitoids and orthogneisses are also consistently
higher than those of DVla hornblende-biotite granitoids.
Chondrite normalised LREE profiles are similar for both the
DVla and DVlb granitoids (Fig. 6), but more evolved DVlb
granitoids are characterised by lower absolute LREE con-
centrations.
Analyses of the "Dun Type" orthogneisses (Cox &
Allibone 1991) appear to form the less evolved extension of
the DVlb biotite granitoid trends, implying the orthogneiss
Dun Pluton is also part of the DVlb suite. Structural
relationships outlined in Allibone et al. (1991) and Cox &
Allibone (1991) imply that emplacement of the Dun Pluton
and other biotite orthogneisses occurred before Fj, isoclinal
folding of the Koettlitz Group (Fig. 3). The simplest
interpretation, consistent with the structural relationships and
geochemistry of the Dun Pluton, is that emplacement of the
DVlb suite spans a significant part of the structural-
metamorphic history of the Koettlitz Group. Radiometric
dating (discussed in Allibone et al. 1993a) indicates an age
difference anywhere between a few million years and 120Ma
separating emplacement of the orthogneiss Dun Pluton and the
major DVlb Hedley, Valhalla, St Johns, and Suess Plutons.
While the shorter time span is perhaps easier to rationalise
with the inferred time scale of tectonomagmatic events,
emplacement of small, petrogenetically associated DVlb suite
intrusives over 120 Ma may imply a relatively stable
tectonomagmatic situation for this length of time.
Fig.4 Major andtraceelement Harkerdiagrams illustrating thedifferences andsimilarities inthechemistry ofthevarious granitoidplutons
andsuites intheDryValleys area.HarkerdiagramsindicatethattheDVla hornblende-biotite granitoids andtheDVlbbiotitegranitoidsform
two,distinct,evolutionary trends."Dun-Type"biotiteorthogneisses (Cox&Allibone 1991)represent themost unevolved oftheDVlbbiotite
granitoids, rather than a separate petrogenetic suite. The Orestes Pluton exhibits DVlb geochemistry, despite havingfieldrelationships and
enclavestypicalofDV2granitoids,whiletheHarker andSwinford Plutons show close affinities withthe DV2suite.TheBrownworthPluton
showsmixed DVla+b andDV2chemical character. Dataarefrom this study, Palmer (1987),Allibone (1988),Ellery (1989), Smillie(1989),
and Cox &Allibone(1991).
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-7-320.jpg)
![400
300
200
100
1000
Ift
55 60 65 70 75 80 55 60 65 70 75 80 55 60 65 70 75 80 55 60 65 70 75 80
•9
O
55 60 65 70 75 80
55 60 65 70 75 80
SiO2
© DVIa granitoid • DV1b granitoid
A DVIaorthogneiss * DVIborthogneiss
55 60 65 70 75
2500
55 60 65 70 75
SiO2
x DV2 granitoid • Brownworth
* Harker
e Swinford
30
25
20
15
10
5
0
Cr
ft a
©© ©
© © a ©
© «© © ©
o
ft xas ©
© ©o©»
X
X L
xaA
e e©
55 60 65 70 75 80
55 60 65 70
SiO2
I'
55 60 65 70 75 80
55 60 65 70 75 80
SiO2
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-8-320.jpg)
![306 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
o DV1 a granitoid
A DVIaorthogneiss
• DV1b granitoid
A DVIborthogneiss
x DV2 granitoid
a Orestes
• Brownworth
* Harker
© Swinford
Fig. 5 Na2O versus K2O plot of granitoid analyses. The DVla
hornblende-biotite granitoids, DVlb biotite granitoids, and DV2
suite quartz-monzonites and granites each define a distinct
evolutionary trend.DVla granitoids arecharacterised by arelatively
shallow negative slope,unlike the steeper negative slope defined by
themoresodicDVlbbiotitegranitoids.TheK2Ocontent oftheDV2
suite appears independent of the Na2Ocontent. Fields of S-typeand
I-type granitoids, after White & Chappell (1983), are plotted for
comparison.Dataarefrom this study,Palmer (1987,1990),Allibone
(1988),Ellery (1989), Smillie (1989), and Cox &Allibone (1991).
Field relationships, petrographic characteristics, and
geochemical data all support the subdivision of the DV1 suite
as defined by Smillie (1992) into two petrogenetically distinct
and unrelated suites. These are the DVla suite consisting of
hornblende-biotite granitoids and a DVlb suite consisting of
biotite granitoids. Hornblende-biotite and biotite ortho-
gneisses described by Cox & Allibone (1991) are inferred to
be integral parts of the DVla and DVlb suites, respectively.
The structural relationships of individual intrusions within
both the DVla and DVlb suites indicates emplacement of
both suites spans at least the later stages of deformation and
metamorphism of the older Koettlitz Group. Consequently,
both the DVla and DVlb suites are inferred to be time
transgressive. Each suite represents a continuum of intrusions,
rather than a distinct, separate, plutonic event at a specific
geologic time (Fig. 3).Thepartly coeval emplacement of these
two unrelated granitoid suites indicates coeval melting of
distinct protoliths.
Comparison of the DV2 suite with the DVla and DVlb
suites
Analyses of the Pearse Pluton and unnamed quartz-monzonite
dikes, plugs, and sills indicate geochemical characteristics
analogous to the DV2 suite as defined by Smillie (1992). The
Pearse Pluton and the unnamed quartz-monzonite dikes,
plugs, and sills both have high K2O, Rb, Pb, and Zr contents
relative to the DVla and DVlb suites (Fig.4,5). Analyses also
show the DV2 suite intrusions are depleted in MgO, CaO, V,
and Cr relative to DVla granitoids, although DV2 suite MgO,
V, and Cr contents are similar to DVlb rocks. In addition, less
evolved samples of the Pearse Pluton and the unnamed quartz-
monzonite dikes are highly enriched in Ba (up to 2500 ppm)
and Sr (up to 900 ppm) (Fig. 4). In both the Ba and Sr versus
SiO2 variation diagrams (Fig. 4) the DV2 suite granitoids
exhibit a steep negative slope, parallel to that defined by the
DVlb suite, but at lower SiO2 values, clearly illustrating the
different evolutionary trends of each suite. Ba and Sr contents
of the DVla suite are lower, with Ba/SiO2 and Sr/SiO2
variation diagrams having a shallower slope than for the DVlb
and DV2 suites, again clearly illustrating the different
evolutionary trends of each suite. The DV2 suite is enriched in
LREE relative to both the DVla and DVlb suites (Fig. 6).
Despite overlap between DVla and DV2 suite Na2O, A12O3,
and Y contents, and DVlb and DV2MgO,Cr, and V contents,
it is apparent that, when the geochemical data are combined
with field relationships, three, rather than two, distinct
petrogenetic suites, as proposed by Smillie (1992), are present
in the Dry Valleys area.
Suite affinities of the Swinford, Brownworth, Orestes,
and Harker Plutons
Field relationships indicate that these four plutons have similar
ages and intrusive styles as the granitoids included in the DV2
suite (Allibone et al. 1993a, fig. 3). Felsic porphyry enclaves
identical to the Vanda dikes, present in each of these plutons,
are also typical of the DV2 suite granitoids described by
Smillie (1992). Analyses of these four plutons are plotted in
Fig. 4, 5, and 6. They indicate the chemistry of these four
plutons deviates from the chemistry characteristic of the DV2
suite as outlined in Smillie (1992).
Analyses of the Swinford Pluton indicate a composition
generally consistent with DV2 suite characteristics. Only the
relatively low K2O and Rb contents of the Swinford Pluton are
inconsistent with its DV2 field relationships and felsic
porphyry enclave suite.The Harker Pluton is the most evolved
granitoid studied. In many variation diagrams (Fig. 4,5,7) the
Harker Pluton plots at the intersection of trends defined by two
or three of the DVla, DVlb, or DV2 suites. Consequently, the
chemistry of the Harker Pluton is generally consistent with it
being part of the DV2 suite, with only the low K2O, Rb, and
Ba contents of the least evolved samples deviating from the
chemical characteristics of the DV2 suite.
The Brownworth and Orestes Plutons exhibit few
chemical features in common with the DV2 suite as defined by
Smillie (1992). This is despite having identical field relation-
ships and enclaves. The chemistry of the Orestes Pluton is
analogous to the older DVlb suite biotite granodiorites and
granites, rather than the DV2 suite. This is consistent with the
lack of hornblende in the Orestes Pluton, an important feature
of the DVlb suite, and unlike the other younger discordant
plutons. The field relationships of the Vanda dikes and the
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-9-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 307
Fig. 6 Chondrite normalised
LREE contents of the granitoid
samples. DV2 suite granitoids are
enriched in LREE relative to DV1a
and DVlb suite granitoids. Small
peaks in each profile probably
reflect the analytical procedure
rather than real differences in the
relative LREE concentrations.
1000r
800
600
400
200
100
80
60
4 0
20
Dry Valleys 1asuite Dry Valleys 1 b suite Dry Valleys 2 suite
+ Orestes Pluton
—-Brownworth Pluton
La Cs Pr Nd La Ce Pr Nd La Ce Pr Nd
Orestes Pluton indicate that the Orestes Pluton is probably the
oldest of the relatively young discordant plutons, with field
relationships and enclaves analogous to the DV2 suite defined
by Smillie (1992). This is consistent with the conflicting
chemistry, field relationships, and enclaves of the Orestes
Pluton, which indicate features in common with both the
DVlb and DV2 suite.
Whether the Brownworth, Orestes, Harker, and Swinford
Plutons are included in the DV2 suite depends on how the
DV2 suite is defined. If field relationships and enclave types
are emphasised in the suite definition, then all four plutons
would be included. Alternatively, if geochemistry is
emphasised, then the Orestes Pluton at least would be included
in the DVlb suite, while the Harker, Swinford, and
Brownworth Plutons would not form part of any chemically
coherent suite. This is analogous to the situation outlined by
Whitten et al. (1987) who suggested numerous different suites
can be defined depending on the combination of criteria
selected. The lack of chemical coherence within these younger
discordant plutons with Vanda felsic porphyry enclaves
indicates amore complex petrogenesis than can beresolved by
a simple suite-style approach. Throughout the remainder of
this paper, only those plutons with field relationships and
chemical characteristics consistent with the original defini-
tion of the DV2 suite are referred to as DV2 suite granitoids.
The Brownworth, Orestes, Swinford, and Harker Plutons are
referred to individually, or as granitoids with apparently
unique combinations of field relationships and chemical
features. This approach is consistent with the implied complex
petrogenesis of the younger granitoids, and is preferable to
squeezing all these plutons into a single suite or defining
multiple suites to accommodate individual plutons.
1000
500 •
200
100 -
50
:Rb
•
•
„—•
o
1 1
Syn-collisional
Volcanic arc
/
1 *
Intraplate
10 20 50 100
Nb+Y
o DV1a
• DV1b
x DV2
• Orestes Pluton
• Brownworth Pluton
+ Harker Pluton
- Swinford Pluton
Fig. 7 Rb versus Nb+Y plot illustrating the depletion of the DV lb
suite biotite granitoids and Orestes Pluton in Nb and Y relative to the
DVla hornblende-biotite granitoids and the DV2 suite. The higher
Rb content of the evolved DV2 suite granitoids relative to the DVla
and DVlb suite granitoids is also apparent. Tectonic setting
discriminant fields, after Pearce et al. (1984), are plotted for
comparison. Data are from this study, Palmer (1987,1990), Allibone
(1988), Smillie (1989), and Ellery (1989).
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-10-320.jpg)
![308 New Zealand Journal of Geology and Geophysics, 1993,Vol. 36
CORRELATION OF PLUTONS AND SUITES WITH
PREVIOUSLY DESCRIBED GRANITOID UNITS IN
SOUTHERN VICTORIA LAND
Many previous workers in southern Victoria Land preferred to
discuss the granitoids of the Dry Valleys area as large-scale
units. These units are inferred here to be similar to suites of
individual plutons, although they were commonly not defined
as such (e.g., Gunn &Warren 1962;McKelvey & Webb 1962;
Allen & Gibson 1962; Haskell et al. 1965a; Skinner 1983;
Findlay 1985,1991). These large-scale units or suites include:
the Pre-tectonic Gneisses, Larsen Granodiorite, and Irizar
Granite initially proposed by Gunn & Warren (1962);
Olympus Granite Gneiss, Dias Granite, Theseus Granodiorite,
and Vida Granite initially proposed by McKelvey & Webb
(1962); and the Kukri Hills, Larsen, and Victoria Intrusive
Groups proposed by Findlay (1985). Some of these large-scale
units were mapped throughout southern Victoria Land and the
Wilson Terrane of northern Victoria Land (e.g., Larsen
Granodiorite, Irizar Granite in Gunn & Warren (1962) and
Skinner & Ricker (1968)). The internal makeup of these larger
scale units is not discussed by many workers, although Gunn
& Warren (1962) noted that the Irizar Granite defined by them
consists of a number of separate plutons, whereas Skinner
(1983) noted that the Larsen Granodiorite is a convenient
name for a family of similar plutons.
Sufficient detailed mapping has now been completed to
allow an attempt at unravelling the relationships between suite
nomenclatural schemes used by previous workers and this
study. This discussion is an addition to the similar discussion
in Smillie (1992), made necessary by the recognition of the
DVla and DVlb suites here.
The larger concordant plutons included in the DVla suite
here were initially included in the Pre-tectonic Gneisses of
Gunn & Warren (1962) and the Dias Granite and Olympus
Granite Gneiss of McKelvey & Webb (1962) and Allen &
Gibson (1962). The relatively small leucocratic Catspaw
Pluton, also included in the DVla suite here, has previously
been described as Irizar Granite by Haskell et al. (1965a).
Subsequent workers have described the major plutons within
the DVla suite as Larsen Granodiorite (Haskell et al. 1965a;
Skinner & Ricker 1968; Skinner 1983) or members of the
Larsen Intrusive Group (Findlay 1985, 1991). Gneissose
margins of the Bonney, Wheeler, Cavendish, and Denton
Plutons were included in the Larsen Intrusive Group by
Findlay (1985), but hornblende-biotite orthogneisses, inferred
here to be genetically associated with these plutons, were
included in the Kukri Hills Group by Findlay (1985).
Plutons included in the DVlb suite here were initially
described as grey granite by, amongst others, Ferrar (1907)
and Mawson (1916), and later named Larsen Granodiorite by
Gunn & Warren (1962). However, subsequent workers (e.g.,
Haskell et al. 1965a; Skinner &Ricker 1968) applied the name
Larsen Granodiorite to plutons here included in the DVla
suite. These and subsequent workers have included DVlb
suite in either the Vida Granite (Allen & Gibson 1962), Irizar
Granite (Haskell et al. 1965a), or Victoria Intrusive Group
(Findlay 1985).
The DV2 suite and plutons with distinct chemistries, but
identical field relationships, were initially described as Irizar
Granite (Gunn & Warren 1962;Haskell et al. 1965a) and Vida
Granite (McKelvey & Webb 1962; Allen & Gibson 1962),
along with other plutons here included in the DVla and DVlb
suites. Most recently, Findlay (1985) included rocks, here
described aspart of the Brownworth Pluton, in the Briggs Hills
Granodiorite, a suite scale subunit of the Larsen Intrusive
Group. Other rocks that form part of the Pearse Pluton were
not assigned by Findlay (1985) to any particular unit.
Many of the individual plutons from each of the three
suites of granitoids identified here have in the past been
assigned to all the major granitoid units used by previous
workers. This reflects the superficial similarity of many of the
plutons in each of the three suites. Geochemical analysis
during this study has sometimes indicated that granitoids
initially assumed to be related on the basis of similar hand-
specimen characteristics are unrelated plutons forming parts
of genetically distinct suites (e.g., Catspaw and Pearse
Plutons). Furthermore, the DVla and DVlb suites are inferred
to be time transgressive, with emplacement of constituent
plutons spanning at least the later stages of deformation in the
adjacent Koettlitz Group (Cox & Allibone 1991). The time-
transgressive nature of the suites defined here differs from the
approach of previous workers who have attempted to
distinguish the older granitoids partly on the basis of their
inferred timing of emplacement relative to folding phases
within the Koettlitz Group (e.g., Skinner 1983;Findlay 1985,
1991). This earlier approach tends to mask the genetic
relationships of the various plutons and has the potential to
separate genetically associated granitoids emplaced at differ-
ent times into different suites, and combine genetically distinct
plutons emplaced at the same time in the same suite, thereby
confusing the petrogenetic interpretation of these granitoids.
As a result of this study, we suggest that future workers
record the shape and internal characteristics of individual
plutons, rather than just summarise their observations by
interpreting larger scale units, as has occurred in the past.
Chemical analyses can then be related back to individual
plutons with clearly defined field relationships, rather than
interpeted suites that may contain unrelated plutons. Given the
repeated inclusion of genetically unrelated plutons in the
following previously defined, larger scale granitoid units, we
would recommend that they be abandoned or confined to
plutons in their respective type areas: Olympus Granite
Gneiss, Larsen Granodiorite, Irizar Granite, Vida Granite,
Dias Granite, Briggs Hills Granodiorite, Larsen Intrusive
Group, Victoria Intrusive Group, Kukri Hills Group, and
Theseus Granodiorite.
CORRELATION WITH NORTHERN
VICTORIA LAND
Background geology
Several recent papers provide sufficient analyses of granitoids
(Borg et al. 1987; Vetter & Tessensohn 1987; Ghezzo et al.
1987; Armienti et al. 1990) from northern Victoria Land to
allow a comparison with the chemistry of granitoids from the
Dry Valleys area, and thereby test correlations made by earlier
workers (e.g., Gunn & Warren 1962; Skinner & Ricker 1968).
Potential correlatives of granitoids from the Dry Valleys area
are those in the westernmost Wilson Terrane of northern
Victoria Land (Stump et al. 1983). Bowers Terrane island arc
tholeiites (Weaver et al. 1984; Bradshaw et al. 1985)
juxtaposed against the eastern margin of the Wilson Terrane
are considered to be allochthonous to the Antarctic Craton
margin. Bradshaw et al. (1985) suggested accretion of the
Bowers Terrane against the Antarctic Craton margin c. 500
Ma ago, postdating emplacement of Cambro-Ordovician
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-11-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 309
Q"
40 60
ANOR
80 100
o DV1a • DV1b x DV2
Mt Abbott Intrusives (MAI)
I ' I I J South Victoria Land Intrusives (SVLI)
Fig. 8 Normative compositions of Dry Valley granitoids plotted in
terms of the Q' and ANOR parameters after Streckeisen & LeMaitre
(1979). Evolutionary trends of the southern Victoria Intrusives
(SVLI) and the Mt Abbott Intrusives (MAI) of northern Victoria
Land, after Armienti et al. (1990), are plotted for comparison. DV1 a
and DVlb granitoids exhibit a similar trend to the SVLI of northern
Victoria Land. The DV2 suite is characterised by a more "syenitic"
evolutionary trend than either the SVLI or MAI.
sg, syenogranite; mg, monzogranite; gr, granodiorite; ton, tonalite;
qs, quartz syenite; qm, quartz monzonite; qmd, quartz monzodiorite;
qd, quartz diorite; sy, syenite; mo, monzonite; md, monzodiorite; di,
diorite.
"Granite Harbour Intrusives" in northern Victoria Land, but
predating emplacement of the Devonian Admiralty Intrusives
in all terranes of northern Victoria Land.
Both Borg et al. (1987) and Vetter & Tessensohn (1987)
mapped dominantly two-mica S-type granites in the western
part of the Wilson Terrane and gabbroic to granitic I-type
granitoids in the eastern part of the Wilson Terrane. An active
continental margin setting for the observed plutonism was
inferred by both Borg et al. (1987) and Vetter & Tessensohn
(1987), with the chemical data of Borg et al. (1987) suggesting
increasing involvement of metasedimentary material in the
granitoid source rocks towards the western part of the Wilson
Terrane. Presumably, subduction ceased immediately to the
east of the Wilson Terrane at c. 500 Ma with accretion of the
adjacent Bowers Terrane.
Unlike Borg et al. (1987) and Vetter &Tessensohn (1987),
Ghezzo et al. (1987) noted significant amounts of I-type
granitoid cropping out in the southern and western parts of the
Wilson Terrane, indicating that the distribution of S-type and
I-type granitoids is more complex than suggested by Borg et
al. (1987) or Vetter & Tessensohn (1987). Armienti et al.
(1990) identified two batholiths comprising three distinct I-
type plutonic complexes of differing petrographic and
chemical character in the Wilson Terrane of northern Victoria
Land. In the southern part of northern Victoria Land, Armienti
et al. (1990) described the "South Victoria Land Intrusives"
(SVLI), which were inferred to be the northern extension of
granitoids cropping out in the Dry Valleys area. The SVLI
range in composition from diorite to leucogranite and include
the granitoids of the Mt Larsen and Cape Irizar areas, which
have previously been correlated with granitoids in southern
Victoria Land (Larsen Granodiorite, Irizar Granite of Gunn &
Warren 1962 and Skinner & Ricker 1968). To the north and
east of the SVLI, the Wilson Terrane is intruded by the
gabbroic to monzogranitic Deep Freeze Range Intrusives
(DFRI) and the syenogranite-dominated Mt Abbott Intrusives
(MAI) (Armienti et al. 1990). The DFRI and MAI in the north
and east of the Wilson Terrane (Lantermann Terrane of
Bradshaw et al. 1985) are separated from the SVLI in the south
and west of the Wilson Terrane (Daniels Terrane of Bradshaw
et al. 1985) by the Priestley Fault (Armienti et al. 1990),
equivalent to the Soza Fault of (Bradshaw et al. 1985) and the
Rennick-Aviator Line of Grew et al. (1984). The Priestley or
Soza Fault corresponds to achange inthe metamorphic history
of the older metasedimentary rocks (Grew et al. 1984). Grew
& Sandiford (1984, 1985) indicate schists hosting the DFRI
east of the Soza/Priestley Fault contain assemblages indic-
ative of metamorphic pressures in excess of 6 kbar. Grew et
al. (1984) and Vetter & Tessensohn (1987) described assem-
blages indicative of peak metamorphic pressures of c. 4 kbar
west of the Priestley/Soza Fault in rocks that host the SVLI.
Correlation
The apparent petrographic similarity of the SVLI and
granitoids of the Dry Valleys area, long recognised by
previous workers (e.g., Gunn & Warren 1962), indicates the
SVLI are the most likely correlatives in northern Victoria
Land of the Dry Valleys granitoids. The MAI are also
compared with granitoids from the Dry Valleys, as their
syenogranite composition is similar to the DV2 suite.
Normative compositions of granitoids from the Dry Valleys
are plotted and compared to the SVLI and MAI of northern
Victoria Land (Armienti et al. 1990) in Fig. 8 (after
Streckeisen & LeMaitre 1979). The DVla and DVlb suites
show a similar evolutionary trend to the SVLI of northern
Victoria Land, ranging in composition from monzodiorite and
quartz-diorite through quartz-monzodiorite and granodiorite,
to monzogranite. However, the evolutionary trend of the DV2
suite from syenite and monzonite through quartz-syenite to
syenogranite is distinctly more "syenitic" than the evolu-
tionary trends of either the SVLI or MAI. Therefore, the DV2
suite does not appear to have any geochemical counterparts in
either the MAI or the SVLI of northern Victoria Land.
Granitoids from the Dry Valleys area are compared further
with the SVLI and MAI of northern Victoria Land in Harker
diagrams (Fig. 9). The Harker diagrams suggest a similarity
between the less evolved parts of the SVLI and the DVla suite
of the Dry Valleys area. However, the SVLI analyses of
Armienti et al. (1990) show significant scatter into the DVlb
field, which is consistent with the presence of biotite
granitoids in the SVLI (Armienti et al. 1990) similar to the
DVlb suite. So-called "Irizar Type" evolved granitoids,
described by Armienti et al. (1990), within the SVLI do not
show any affinity with the DV2 suite from the Dry Valleys
area, despite their similar appearance in hand specimen.
Rather, granitoids from the Cape Irizar area of northern
Victoria Land appear similar in chemical character to the
evolved DVla suite Catspaw Pluton. Comparison of the MAI
with the Dry Valleys granitoids indicates a weak similarity to
the DV2 suite, although evolutionary trends on the Harker
diagrams do not generally overlap.
The limited data available indicate that the DVla suite in
the Dry Valleys area could be a southern extension of the
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-12-320.jpg)
![310 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
3 •
65_._ 70
SiO2
CaO
:X
•
. +•••-.
200-
100•
40
Volcanic arc granitoid intraplate
To ' 20 40 60 i6<
Nb+Y
C ! ? DVIaSuite
C t3 DV1b Suite
•:
:• DV2 Suite
+
o
South Victoria Land Intrusives (SVLI)
Ml Abbott Intrusives (MAI)
Fig. 9 Harker diagrams com-
paring the evolutionary trends of
the DVla, DVlb, and DV2 suites
in the Dry Valleys area (from Fig.
4) with the SVLI and MAI of
northern Victoria Land. Analyses
of the SVLI and MAI are taken
from Armienti et al. (1990). The
SVLI shows similar geochemical
character to both the DVla and
DVlb suites. The DV2 suite
exhibits different evolutionary
trends to either the SVLI or MAI,
albeit with more similarities to the
MAI than theSVLI.
SVLI, with both "Larsen Type" and "Irizar Type" granitoids
of Armienti et al. (1990) being represented by the DVla suite.
However, further data are required to assess whether the
DV1b suite also occurs in the SVLI of northern Victoria Land.
No direct correlative of the DV2 suite appears to be present in
the SVLI, as the "Irizar Type" granitoids of Armienti et al.
(1990) display different evolutionary trends. This is an
important conclusion because granitoids here included in the
DV2 suite in the Dry Valleys area have previously been
widely correlated with the granitoids of the Cape Irizar
area in northern Victoria Land (e.g., Gunn & Warren 1962;
Haskell et al. 1965a; Skinner & Ricker 1968; Skinner 1983).
Furthermore, Vanda mafic and felsic dike swarms also appear
to be absent from the SVLI of northern Victoria Land.
Correlation of the SVLI of northern Victoria Land with the
older granitoids of the Dry Valleys area is compatible with the
metamorphic history of the host metasedimentary rocks.
Koettlitz Group metasediments of the Dry Valleys area were
inferred to have been metamorphosed at 700-750°C and 4-5
kbars (Murphy 1971;Allibone 1992; Cox 1992), similar to the
metamorphic history inferred for the host rocks of the SVLI
west of the Soza/Priestley Fault or Rennick-Aviator Line, but
distinct from that inferred for the host rocks of the DFRI, east
of the Soza/Priestley Fault (Grew & Sandiford 1984, 1985;
Grew et al. 1984; Vetter & Tessensohn 1987; Talarico et al.
1987).
CORRELATION WITH THE CENTRAL
TRANSANTARCTIC MOUNTAINS
McGregor (1965) and Haskell et al. (1965b) mapped a variety
of granitoids including inferred pre-, syn-, and post-tectonic
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-13-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 311
plutons within the Queen Maud Batholith of the central
Transantarctic Mountains, south of the Dry Valleys. Sub-
sequently, Borg (1983) noted a similar variety of granitoids,
and subdivided these granitoids into S-types, more common in
the western part of the Queen Maud Batholith adjacent to the
Antarctic Craton margin, and I-types dominating the eastern
part of the batholith. Haskell et al. (1965b) initially noted the
petrographic similarity of some rocks in the Queen Maud
Batholith and granitoids of the Dry Valleys area. Based on an
interpretation of radiometric dates and this apparent petro-
graphic similarity, Skinner (1983) suggested a correlation
between the Carlyon Granodiorite (an integral part of the
Queen Maud Batholith) and Larsen Granodiorite of the Dry
Valleys area, here interpreted as partly equivalent to the
DVla suite. However, Findlay (1991) noted that the Carlyon
Granodiorite contains hypersthene and muscovite, unlike the
Larsen Granodiorite/Intrusive Group, and questioned this
correlation.
More recently, Borg et al. (1990) described regional
variations in the isotopic character of granitoids between the
Nimrod Glacier and Gabbro Hills in the central Transantarctic
Mountains, south of the Dry Valleys area. Cambrian-
Ordovician granitoids in the westernmost Miller Range that
intrude Precambrian metasediments forming the easternmost
part of the Antarctic Craton are characterised by 87
Sr/86
Sr; in
the range 0.73243-0.74174. Cambrian-Ordovician granitoids
further to the east, between the Marsh Glacier and Shackleton
Glacier, are characterised by lower initial 87
Sr/86
Sr; ratios in
the range 0.70684-0.71906. Granitoids in the Gabbro Hills
area east of the Shackleton Glacier are characterised by the
lowest initial 87
Sr/86
Sri ratios of 0.70446-O.70589. These
variations in isotopic character are consistent with the west-
east change from S-type to I-type granitoids previously
described by Borg (1983).
Lack of published whole-rock analyses from granitoids of
the Queen Maud Batholith prevents direct comparison with
the chemistry of the DVla, DVlb, and DV2 suites of the Dry
Valleys area. The lack of S-type granitoids in the Dry Valleys
area is a fundamental difference, although similar rocks may
be present beneath the ice cap to the west. Available Sr-isotope
analyses from the Dry Valleys area (see discussion in Allibone
et al. 1993a), including granitoids from the DVla, DVlb, and
DV2 suites, exhibit a similar range of 87
Sr/86
Sr; to the
granitoids cropping out between the Marsh and Shackleton
Glaciers in the central Transantarctic Mountains.
Borg et al. (1990) inferred the area between the Marsh and
Shackleton Glaciers, referred to as the Beardmore Micro-
continent, is allochthonous to the east Antarctic Craton, on the
basis of the isotopic character of the Cambrian-Ordovician
granitoids. Stratigraphic and intrusive relationships constrain
the timing of accretion of the Beardmore Microcontinent to
between 760 and 550 Ma (Borg et al. 1990). Granitoids
cropping out between the Marsh and Shackleton Glaciers,
with Sr-isotopic compositions similar to the Dry Valleys
granitoids, were inferred to be derived from thinned Pre-
cambrian continental crust (Borg et al. 1990). Additional Sr,
Nd, and Pb isotopic data are required to adequately describe
the granitoids of the Dry Valleys area and assess whether the
crustal and tectonic model developed for the central Trans-
antarctic Mountains by Borg et al. (1990) is applicable to the
Dry Valleys area. The presence of at least three granitoid
suites in the Dry Valleys area suggests considerable subtle
complexity not yet recognised in the central Transantarctic
Mountains area, or perhaps not present.
PETROGENESIS, SOURCE CRITERIA, AND
TECTONIC SETTING OF THE DVla, DVlb, AND
DV2 SUITES
Smillie (1992) inferred a subduction-related, continental arc
setting associated with generation and emplacement of the
DV1 suite, based on the characteristics of the DVla Bonney
Pluton. Recognition of two fundamentally distinct DVla and
DVlb suites, initially included in the DV1 suite of Smillie
(1992), requires some reassessment of the source rocks and
tectonic setting associated with emplacement of these rocks.
Smillie (1992) inferred the younger DV2 suite was emplaced
during postsubduction extension as a result of melting of I-
type crustal material. It is possible that this occurred in
response to emplacement of mantle-derived mafic rocks,
perhaps represented by the shoshonites described by Keiller
(1991), which crop out extensively throughout southern
Victoria Land. Recognition of the geochemical complexity
and conflicting chemical characteristics of the younger
granitoids, with similar relative ages and enclave suites to
those defined as members of the DV2 suite by Smillie (1992),
requires reassessment of the petrogenesis of these younger
granitoids as well.
Source criteria and petrogenesis of DVla and DVlb
suites
Smillie (1992) clearly demonstrated the I-type characteristics
of the DVla Bonney Pluton. This interpretation was based on
the hornblende-clinopyroxene bearing assemblages, abun-
dance of mafic enclaves, and relatively metaluminous, calcic,
and sodic composition compared with S-type granitoids. The
essentially identical characteristics of the other DVla
granitoids described by Allibone et al. (1993a, b) and Cox &
Allibone (1991) are also consistent with an I-type classi-
fication. Rb, Sr, Na2O, K2O,and A12O3contents of these rocks
are similar to those documented in Cordilleran I-type
granitoids developed in volcanic arcs along continental
margins (e.g., Atherton & Sanderson 1985).
The DVlb suite is characterised by several features not
typical of continental arc granitoids. These include the
restricted compositional range, between 64 and 76 wt% SiO2,
the extreme enrichment in Sr and to a lesser extent Na2O and
A12C<3, and the extreme depletion in Y and Nb, while
maintaining LREE contents comparable to typical I-type
granitoids. This set of petrographic and geochemical features
is not typical of either S-type or I-type granitoids as described
by White &Chappell (1983).DVlb suite Sr,Na2O, andA12O3
contents are considerably higher and exhibit steeper negative
correlations with SiO2 than typical Cordilleran I-type
granitoids, similar to the DVla suite rocks (e.g., Atherton &
Sanderson 1985), although these features are partly analogous
to the chemistry of tonalites and trondhjemites (e.g., Manduca
et al. 1992; Barnes et al. 1992).
The high Sr content of the DVlb granitoids implies
advanced melting of a dominantly quartzofeldspathic source
in which plagioclase is not a residual phase. Alternatively, it
may indicate a lesser degree of partial melting in a source rich
in refractory minerals such as garnet and pyroxene, again
where plagioclase is not a residual phase (e.g., Anderson &
Cullers 1987, 1990; Tulloch & Rabone 1987; Manduca et al.
1992; Wyborn et al. 1992). Advanced melting of a quartzo-
feldspathic protolith is consistent with the overall grano-
dioritic composition of the DVlb suite. The extreme deple-
tion in Y implies the presence of a refractory phase that
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-14-320.jpg)
![312 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
preferentially incorporates Y (and HREE) in the residual
material, such as garnet. Lack of significant garnet within all
but the most evolved DVlb granitoids would be consistent
with only relatively minor residual garnet in a dominantly
quartzofeldspathic protolith. Garnet present in the most
evolved DVlb granitoids is inferred to have crystallised from
the melt during emplacement, since the most evolved DVlb
suite granitoids tend towards peraluminous compositions
(also reflected in the presence of muscovite accompanying
garnet).
The source material for the DVlb suite must also be
capable of producing a granitoid melt with an initial 87
Sr/86
Sr
ratio around 0.708-0.709. This initial 87
Sr/86
Sr ratio is
significantly higher than tonalitic and trondhjemitic rocks
with superficially similar Sr, Na2O, and AI2O3 enriched
chemistries, that are commonly inferred to have been derived
by either partial melting, or fractional crystallisation of
primitive basaltic material. Furthermore, the DVlb suite is
significantly enriched in K2O and Rb compared to tonalitic
and trondhjemitic rocks, which is reflected in the granodiorite
and granite compositions. The restricted range of quartzo-
feldspathic compositions implies the DVlb suite was derived
from a similar relatively felsic, homogeneous source, rather
than by fractional crystallisation of more mafic melts, which
would produce dioritic and monzodioritic or tonalitic
intrusives as well.
Potential source rocks that could account for the character-
istics of the DVlb suite include older, garnet-bearing,
metaluminous granitoids or relatively immature meta-
sediments. Melting of more mature sediments with pelitic
compositions would give rise to granitoids with more typical
S-type features, including peraluminous compositions and
higher initial 87
Sr/86
Sr ratios. However, immature sediments
containing relatively little material derived from old Archean
and early Proterozoic sources could produce granitoid melts
with bulk rock compositions and isotopic characteristics
analogous to the DVlb suite. In order to account for the Y
depletion, some garnet would need to be present in this
metasedimentary protolith.
Garnet and two-mica granodiorites and granites with
chemistries similar to the DVlb suite have recently been
described by Anderson & Cullers (1990) from the lower plate
of the Whipple Mountain Metamorphic Core Complex. The
grosssular-rich garnet compositions in these granitoids
indicate crystallisation at pressures between 7.5 and 9 kbars,
indicative of arelatively deep level of emplacement. Anderson
& Cullers (1990) inferred that these granitoids were derived
during partial melting of calcic greywackes, derived from a
continental margin volcanic arc, metamorphosed to refractory
garnet and omphacite-bearing, eclogite fades assemblages.
Partial melting of garnet-bearing, eclogite facies rocks was
invoked to explain the unusually high Sr content and depleted
Y content of these granitoids. This hypothesis is consistent
with petrologic evidence of a deep level of emplacement.
Similar hypotheses involving partial melting at extreme
depths have been invoked to explain the analogous chemistry
of granitoids described by Wyborn et al. (1992), Norman et al.
(1992), and Williamson et al. (1992). However, none of these
other studies describe direct petrologic evidence of a deep
level during granitoid emplacement.
An analogous model could be postulated to account for the
geochemical characteristics of the DVlb suite. Volcanogenic
sediment underplated along the west-dipping subduction zone
inferred to have been associated with DVla plutonism is a
potential source for the DVlb suite. However, unlike the
Whipple Mountain Metamorphic Core Complex granitoids,
there is no direct evidence of a deep level of emplacement or
generation for DVlb plutonism. Instead, most of the geologic
evidence appears to contradict such a model. Clinopyroxene
grains in the DVlb suite Dun Pluton have Fe-rich salitic
compositions, without any trace of Al or Na that would be
expected if they had crystallised under relatively high
pressures. Field evidence indicates that the younger DVlb
plutons are discordant, with irregular intrusion breccias
developed along their margins. This contrasts with the
concordant margins typical of granitoids emplaced at deeper
levels. Any inference that the DVlb suite was derived from
melting of sediments or plutonic rocks metamorphosed to
eclogite facies assemblages would have to be based solely on
the Sr-enriched and Y-depleted chemistry of these rocks,
rather than a combination of petrologic and chemical data
as in the Whipple Mountain Metamorphic Core Complex
(Anderson & Cullers 1990). Garnet development in meta-
morphic rocks over a wide range of temperatures, pressures,
and whole-rock compositions indicates that these chemical
features need not be indicative of partial melting at extreme
depths, provided all available plagioclase in the protolith is
consumed during partial melting.
What is clear is that the DVlb protolith was characterised
by a distinct composition and mineral assemblage compared
with the partly coeval DVla suite, which implies coeval
melting of distinct source rocks in different parts of the crust
and possibly upper mantle.
Petrogenesis of the DV2 suite and the Harker, Swinford,
Orestes, and Brownworth Plutons
The different chemical characteristics of these individual
plutons and the DV2 suite require explanation. Each of these
individual plutons and others included in the DV2 suite are
inferred to have broadly similar ages, and all contain
microgranitoid enclaves identical to the Vanda felsic porphyry
dikes. Given these similar field relationships, a correspond-
ing similar, coherent geochemistry would be expected.
Variation in the chemistry of these granitoids may be caused
by several processes or combinations of processes. These
could include melting of a chemically inhomogeneous source,
different amounts of contamination possibly by older DVla
and DVlb granitoids, or subtle differences in the amount of
fractional crystallisation within individual plutons during
emplacement.
Any model proposed to explain the characteristics of these
plutons, which involves contamination of an "end member"
DV2 melt, comparable to the least evolved parts of the Pearse
or Rhone Plutons (Smillie 1992), must account for the
selective changes in the concentration of only some of the
chemical parameters relative to the inferred "end member"
DV2 melt. For example, the chemistry of the Harker and
Swinford Plutons is largely consistent with the DV2 suite
except for the low K2O and Rb contents. This indicates any
contaminant in these two plutons has only affected these two
parameters. In contrast, the Orestes Pluton exhibits chemical
characteristics almost completely consistent with the DVlb
suite. Furthermore, the lack of widespread, partially assim-
ilated xenoliths in any of these younger plutons is difficult to
reconcile with a contamination hypothesis.
Alternatively, intrusion of DV2 suite granitoids may have
been accompanied by partial melting of older DVla and
DVlb suite granitoids, which were emplaced at deeper levels
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-15-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 313
than those currently exposed in the Dry Valleys area. In this
hypothesis, little interaction is inferred between the melt that
crystallised to form the DV2 suite plutons and other melts that
produced the Harker, Swinford, Orestes, and Brownworth
Plutons. This is distinct from the contamination hypothesis,
where incorporation of xenolithic material during emplace-
ment is the process controlling the chemistry of the resulting
granitoid plutons.
Liquid-crystal fractionation, particularly in more felsic
granitoids, is widely postulated as the cause of significant
enrichment or depletion of granites in some incompatible trace
elements (e.g., Champion & Chappell 1992). At high SiO2
contents, relatively small amounts of crystal fractionation can
markedly affect the content of some trace elements. The
evolved compositions of the Orestes and Harker Plutons, in
particular, are consistent with liquid-crystal fractionation
being an important control on the chemistry of these
granitoids. Similar suites of granitoids with incoherent
chemistries are mentioned by Wyborn et al. (1992), who
referred to these rocks as "melt-rich" granitoids as opposed to
"restite-rich" granitoids. Wyborn et al. (1992) suggested the
distinctive compositions of individual plutons reflects the
melt-rich character of these intrusions during their emplace-
ment. This allows each intrusion to independently undergo
crystal-liquid fractionation, resulting in distinct chemistries
developing, despite similar ages and field relationships. A
similar hypothesis could be invoked to explain the different
chemistries of the younger granitoid plutons in the Dry
Valleys area. This would imply that all the younger plutons are
derived from the same source, and are closely related, which is
consistent with their field relationships.
The relative importance of crystal-liquid fractionation and
melting of an inhomogeneous source cannot be currently
determined. Each is potentially capable of explaining the
variations in chemisty between these younger granitoids.
Tectonic synthesis: evolving plutonism along the early
Paleozoic Antarctic Craton margin
Field relationships, geochemistry, and radiometric dating
indicate several marked changes in the nature of granitoid
plutonism in the Dry Valleys area. These changes in the
character of granitoid plutonism are inferred to reflect
concurrent changes in the tectonic setting of the Cambrian-
Ordovician Antarctic Craton margin. The earliest plutonism is
dominated by the DVla suite with concurrent, but minor,
DVlb plutonism. Given the similarity of the DVla suite to
granitoids generated along continental margin arcs, a
subduction setting is inferred at this time. Concurrent
emplacement of small DVlb suite intrusions indicates minor
melting of a distinctly different protolith. This protolith may
have been small amounts of underplated metasediment
derived from the arc associated with DVla plutonism.
Termination of DVla suite plutonism was followed by
emplacement of all the major DVlb suite plutons (Hedley,
Valhalla, Suess, St Johns), marking a distinct change in the
nature of granitoid plutonism along the early Ordovician
Antarctic Craton margin. Radiometric dating of the St Johns
Pluton indicates emplacement of this pulse of DVlb plutons
occurred at 490 ± 14 Ma (Allibone et al. 1993a). The cause of
this marked change in the style and chemistry of granitoid
plutonism is unclear. However, it coincides with the inferred
timing of accretion of the Bowers Terrane along the Antarctic
Craton margin in northern Victoria Land (Bradshaw et al.
1985) at c. 500 Ma. Cessation of DVla plutonism in southern
Victoria Land before c. 490 Ma, could indicate either a
cessation of subduction altogether, or a radical change in the
style of subduction. Cessation of subduction at this time in
southern Victoria Land would be consistent with a similar
accretion event. The pulse of DVlb plutonism emplaced at
c. 490 Ma may reflect increased amounts of sediment
underplated during such an accretion event, although this
inference is highly speculative. Such an accreted terrane may
now form the seafloor east of the current southern Victoria
Land coast, along strike from the Bowers Terrane in northern
Victoria Land. Clasts of volcanics and low-grade meta-
sediment occurring in basal Devonian conglomerates of the
overlying Beacon Supergroup throughout the Olympus and St
Johns Ranges (Allibone et al. 1993b) have no obvious
provenance in present-day southern Victoria Land. These
rocks may be derived from this postulated allochthonous
terrane.
Emplacement of the DVlb suite was followed within 10
Ma or less by intrusion of the Vanda mafic dikes and
associated felsic porphyry dikes. Keiller (1991) concluded that
these were generated at the base of the crust by interaction of a
mantle melt and a crustal component. Subsequent evolution
was dominated by fractional crystallisation of alkali felspar.
Field relationships indicate emplacement of the dikes was
essentially contemporaneous with the beginning of DV2
alkali-calcic, Caledonian I-type magmatism. Analogous
granitoids elsewhere are inferred to have developed in some
type of extensional setting unrelated to subduction (Smillie
1992). Correlations inferred here suggest these later post-
subduction granitoids and dikes do not occur in northern
Victoria Land, indicating different Cambrian-Ordovician
tectonomagmatic histories along the length of the Paleozoic
Antarctic Craton margin between c. 486 and 450 Ma.
SUMMARY AND CONCLUSIONS
Chemical analyses of granitoids emplaced before the prom-
inent Vanda mafic and felsic dike swarms in southern Victoria
Land, indicate the existence of the distinct Dry Valleys la
(DVla) and Dry Valleys lb (DVlb) suites. The DVla suite
includes the batholithic-scale Bonney Pluton and at least four
other major plutons of hornblende-biotite granitoid, as well as
hornblende-biotite orthogneisses described by Cox &
Allibone (1991). The DVlb suite includes several large
plutons of biotite granodiorite and granite, and younger
plugs of biotite granite (partly equivalent to the Theseus
Granodiorite of McKelvey & Webb 1962), as well as biotite
orthogneisses and the "Dun Type" orthogneisses of Cox &
Allibone (1991). Field relationships indicate that emplace-
ment of the older orthogneisses in both suites overlap, but the
majority of DVla plutons, including the Bonney Pluton,
predate emplacement of a major pulse of DVlb plutons.
Radiometric dating indicates emplacement of the DVla and
DVlb suites occurred before c. 490 Ma (Allibone et al.l993a).
Younger granitoids emplaced after the majority of the
Vanda mafic and felsic dike swarms, include the large Pearse
and Nibelungen Plutons and other smaller bodies with
chemistries analogous to the DV2 suite of Smillie (1992).
Other relatively young granitoids (e.g., Orestes, Brownworth,
Harker, and Swinford Plutons) were emplaced at the same
time as the DV2 suite granitoids and contain identical felsic
porphyry enclaves but they have variable geochemistries and
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-16-320.jpg)
![314 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
do not form part of a chemically coherent suite. DV2
granitoids and other plutons with analogous field relationships
and enclaves, but different chemistries, were emplaced
between c. 486 and 450 Ma.
Comparison of granitoids from the Dry Valleys area with
the "South Victoria Land Intrusives" of northern Victoria
Land described in Armienti et al. (1990) indicates potential
correlatives of the DVla and possibly DVlb suites. DV2 suite
rocks from the Dry Valleys area, previously correlated with
the evolved granitoids of Cape Irizar, are distinctly more
monzonitic to syenitic in character. The only potential
correlative of the Cape Irizar granitoids so far mapped in
southern Victoria Land is the evolved DVla Catspaw Pluton.
Sparse Sr-isotope data suggest granites of the Dry Valleys area
are possible correlatives of granitoids cropping out between
the Shackleton and Marsh Glaciers in the central Trans-
antarctic Mountains (Borg et al. 1990).
The geochemistry and abundance of mafic enclaves in the
DVla suite plutons is typical of Cordilleran style I-type
granitoids, and they are inferred to have developed above a
subduction zone along an active continental margin. Chemical
characteristics of the relatively leucocratic DVlb suite are
more unusual. In particular, the very high Sr, A12O3 and Na2O
contents, coupled with extremely low Y contents, indicate a
source region lacking residual plagioclase, but containing
garnet. Partly analogous granitoids elsewhere are inferred to
have been derived from an eclogite fades protolith. However,
no direct geologic evidence exists of such a source for the
DVlb suite,other than the similar chemistry. The source of the
DVlb suite granitoids is unclear although they may be derived
from underplated volcanogenic sediments derived from the
arc associated with DVla suite plutonism. The marked pulse
of DVlb suite plutons corresponds to the timing of accretion
of the Bowers Terrane in northern Victoria Land at c. 500 Ma
and may reflect a similar accretion event in southern Victoria
Land. The younger DV2 suite granitoids are analogous to
Caledonian style I-type granitoids thought to be related to
uplift and extension rather than subduction processes.
The following speculative sequence of events is proposed
to account for changes in the characteristics of granitoids
along the Cambrian-Ordovician Antarctic Craton margin.
Subduction-related Cordilleran style magmatism dominated
before c. 500 Ma. At c. 500-490 Ma, Cordilleran type
plutonism ceased and was replaced by a short pulse of
DVlb plutonism characterised by Sr, Na and Al enriched, and
Y depleted geochemistry, suggesting partial melting of garnet-
bearing source rocks lacking residual plagioclase. These
unusual granitoids may have been derived from sediment
underplated along the subduction zone associated with
Cordilleran plutonism. This pulse of DVlb suite plutonism
may have developed in response to collision between an
allochthonous terrane and the Antarctic Craton margin,
marking the end of subduction-related plutonism. Later DV2
and related younger plutons are inferred to have been
emplaced during postcollision uplift and extension, from
c. 486 to 455 Ma.
ACKNOWLEDGMENTS
The authors thank D. Craw and R. D. Johnstone for their discussion
and critical comments that considerably improved this paper. P. J.
Forsyth, R. D.Johnstone, and M. Hunter are thanked for maintaining
a sense of humour while crushing rocks and making XRF disks. S.
Ness and A. Chappell are thanked for access to XRF facilities at
JCU. In this paper we have drawn conclusions from data and
observations of K. Palmer, I. J. Graham, I. G. Keiller, S. Ellery, R. J.
Sewell, and I. M. Turnbull in addition to our own. Reviews by S. D.
Weaver, J. D. Bradshaw, and R. H. Findlay resulted in considerable
improvement to the paper. Fieldwork was made possible by The
Ross Dependency Research Committee, Antarctic Division (DSIR)
and VXE-6 squadron (U.S. Navy).
REFERENCES
Allen, A. D.; Gibson, G. W. 1962: Geological investigations in
southern Victoria Land, Antarctica. Part 6: Outline of the
geology of the Victoria Valley region. New Zealand journal
of geology and geophysics 5: 234-242.
Allibone, A. H. 1988: Koettlitz Group meta-sediments and
intercalated orthogneisses from the mid Taylor Valley and
Ferrar Glacier regions. Unpublished M.Sc. thesis, lodged in
the Library, University of Otago, New Zealand.
Allibone, A. H. 1992: Low pressure/high temperature
metamorphism of Koettlitz Group schists in the Taylor
Valley and Ferrar Glacier area, South Victoria Land,
Antarctica. New Zealandjournal of geology andgeophysics
35: 115-127.
Allibone, A. H.; Forsyth, P. J.; Sewell, R. J.; Turnbull, I. M.;
Bradshaw, M. A. 1991: Geology of the Thundergut area,
southern Victoria Land, Antarctica. 1:50 000 miscell-
aneous series map 21 (with supplementary text).
Wellington, New Zealand. Geology and Geophysics
Division, Department of Scientific and Industrial Research.
Allibone, A. H.; Cox, S. C.; Graham, I. J.; Smillie, R. W.; Johnstone,
R. D.; Ellery, S. G.; Palmer, K. 1993a: Granitoids of the Dry
Valleys region, southern Victoria Land, Antarctica: plutons,
field relationships, and isotopic dating.New Zealandjournal
of geology and geophysics 36: 281-297 (this issue).
Allibone, A. H.; Heron, D. W.; Forsyth, P. J.; Turnbull, I. M. 1993b:
Geology of the St Johns Range, southern Victoria Land,
Antarctica. 1: 50 000 miscellaneous series map (with
supplementary text). Lower Hutt, New Zealand. Institute of
Geological and Nuclear Sciences.
Anderson, J. L.; Cullers, R. L. 1987: Crust-enriched, mantle-derived
tonalites in the early Proterozoic Penokean Orogeny of
Wisconsin. Journal of geology 95: 139-154.
Anderson, J. L.; Cullers, R. L. 1990:Middle to upper crustal plutonic
construction of a magmatic arc; An example from the
Whipple Mountains Metamorphic Core Complex.
Geological Society of America memoir 174:47-69.
Armienti, P.; Ghezzo, C.; Innocenti, F.; Manetti, P.; Rocchi, S.;
Tonarini, S. 1990: Isotope geochemistry and petrology of
granitoid suites from the Granite Harbour Intrusives of the
Wilson Terrane, North Victoria Land, Antarctica. European
journal of mineralogy 2: 103-123.
Atherton, M. P.; Sanderson, L. M. 1985:The chemical variation and
evolution of the super-units of the segmented Coastal
Batholith. In: Pitcher, W. S.; Atherton, M. P.; Cobbing, E. J.;
Beckinsale, R. D. ed. Magmatism at a plate edge: The
Peruvian Andes. Glasgow, Blackie & Son Ltd. Pp. 208-227.
Barnes, C. G.; Barnes, M. A.; Kistler, R. W. 1992: Petrology of the
Caribou Mountain Pluton, Klamath Mountains, California.
Jounal ofpetrology 33: 95-124.
Borg, S. G. 1983: Petrology and geochemistry of the Queen Maud
batholith, central Transantarctic Mountains with
implications for the Ross Orogeny. In: Oliver, R. L.; James,
P. R.; Jago, J. B. ed. Antarctic earth science. Canberra,
Australian Academy of Science and Cambridge, Cambridge
University Press. Pp. 165-169.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-17-320.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 315
Borg, S. G.; Stump, E.; Chappell, B. W.; McCulloch, M. T.;
Wyborn, D.; Armstrong, R. L.; Holloway, J. R. 1987:
Granitoids of northern Victoria Land, Antarctica: impli-
cations of chemical and isotopic variations to regional
crustal structure and tectonics. American journal of science
287: 127-169.
Borg, S. G.; DePaolo, D. J.; Smith, B. M. 1990: Isotopic structure
and tectonics of the central Transantarctic Mountains.
Journal of geophysical research 95: 6647-6667.
Bradshaw, J. D.; Weaver, S. D.; Laird, M. G. 1985: Suspect
terranes and Cambrian tectonics in northern Victoria Land,
Antarctica. In: Howell, D. G. ed. Tectonostratigraphic
terranes in the Circum Pacific region. Circum-Pacific
Councilfor Energy and Mineral Resources—earthscience
series 1: 493-514.
Champion, D. C.; Chappell, B. W. 1992: Petrogenesis of felsic I-
type granites: an example from northern Queensland.
Transactions of the Royal Society of Edinburgh earth
sciences 83: 115-126.
Cox, S. C. 1989: Gneiss geology—a structural perspective of
foliated granitoids and their host rocks in the Wright Valley,
South Victoria Land, Antarctica. Unpublished M.Sc. thesis,
lodged in the Library, University of Otago, New Zealand.
Cox, S. C. 1992: Garnet-biotite geothermometry of Koettlitz Group
metasediments, Wright Valley, South Victoria Land,
Antarctica. New Zealandjournal of geology and geophysics
35: 29-40.
Cox, S. C. 1993: Inter-related plutonism and deformation in South
Victoria Land, Antarctica. Geological magazine 130: 1-14.
Cox, S. C.; Allibone, A. H. 1991: Petrogenesis of granitoid
orthogneisses from the Dry Valleys region, south Victoria
Land, Antarctica. Antarctic science 3: 405-417.
Ellery, S. G. 1989: Lower Wright geology. Unpublished M.Sc.
thesis, lodged in the Library, University of Otago, New
Zealand.
Ferrar, H. T. 1907: Report on the field geology of the region
explored during the "Discovery" Antarctic expedition.
National Antarctic Expedition 1901-04 natural history
reports 1: 1-100.
Findlay, R. H. 1985: The Granite Harbour Intrusive Complex in
McMurdo Sound: progress and problems. New Zealand
Antarctic record 6 (3): 10-22.
Findlay, R. H. 1991: Antarctica. In: Nairn, A. E. ed. The Phan-
erozoic of the World, Vol. A, The Palaeozoic. Amsterdam,
Elsevier Publishing Company. Pp. 335-421.
Ghezzo, C.; Baldelli, C.; Biagini, L.; Carmignani, L.; Di Vincenzo,
G.; Gosso, G.; Lelli, A.; Lombardo, B.; Montrasio, A.;
Pertusati, P. C.; Salvini, F. 1987: Granitoids from the David
Galcier-Aviator Glacier segment of the Transantarctic
Mountains, North Victoria Land, Antarctica. Geological
Society of Italy memoirs 33: 143-159.
Grew, E. S.; Sandiford, M. 1984: A staurolite-talc assemblage in
tourmaline-phlogopite-chlorite schist from northern
Victoria Land, Antarctica, and its petrogenetic significance.
Contributions to mineralogy and petrology 87: 337-350.
Grew, E. S.; Sandiford, M. 1985: Staurolite in a garnet-hornblende-
biotite schist from the Lantermann Range, northern Victoria
Land, Antarctica. Neues Jahrbuch fur Mineralogie
Monatschefte, Heft. 9: 396-410.
Grew, E. S.; Kleinschmidt, G.; Schubert, W. 1984: Contrasting
metamorphic belts in northern Victoria Land, Antarctica.
GeologischesJahrbuch. B 60:253-263.
Gunn, B. M.; Warren, G. 1962: Geology of Victoria Land between
the Mawson and Mulock Glaciers, Antarctica. NewZealand
GeologicalSurvey bulletin 71.
Haskell, T. R.; Kennett, J. P.; Prebble, W. M.; Smith, G.; Willis,
I. A. G. 1965a: The geology of the middle and lower Taylor
Valley of southern Victoria Land, Antarctica. Transactions
of the Royal Society of New Zealand 2: 169-186.
Haskell, T. R.; Kennett, J. P.; Prebble, W. M. 1965b: The geology of
the Brown Hills and Darwin Mountains, southern Victoria
Land, Antarctica. Transactions of the Royal Society of New
Zealand 2: 231-248.
Keiller, I. G. 1991: Wright dikes—a geochemical study of dike-
forming rock types within the Wright Valley, Southern
Victoria Land, Antarctica. Unpublished M.Sc. thesis,
lodged in the Library, University of Otago, New Zealand.
McGregor, V. R. 1965: Geology of the area between the Axel
Heiberg and Shackleton Glaciers, Queen Maud Range,
Antarctica. Part 1: Basement complex, structure and glacial
geology. New Zealandjournal of geology and geophysics8:
314-343.
McKelvey, B. C.; Webb, P. N. 1962: Geological investigations in
Southern Victoria Land, Antarctica. Part 3: Geology of
Wright Valley. New Zealand journal of geology and
geophysics 5: 143-162.
Manduca, C. A.; Silver, L. T.; Taylor, H. P. 1992: 87
Sr/86
Sr and18
O/
16
O isotopic systematics and geochemistry of granitoid
plutons across a steeply-dipping boundary between con-
trasting lithospheric blocks in western Idaho.Contributions
to mineralogy andpetrology 109:355-372.
Mawson, D. 1916: Petrology of rock collections from the mainland
of southern Victoria Land. Report of the British Antarctic
Expedition 1907-09 geology 1:201-237.
Murphy, D. J. 1971:The petrology and deformational history of the
basement complex, Wright Valley, Antarctica, with special
reference to the origin of augen gneisses. Unpublished Ph.D.
thesis, lodged in the library, University of Wyoming. 114p.
Norman, M. D.; Leeman, W. P.; Mertzman, S. A. 1992:Granites and
rhyolites from the northwestern USA: temporal variation in
magmatic processes and relations to tectonic setting.
Transactions of the Royal Society of Edinburgh earth
sciences 83: 71-81.
Norrish, K.; Chappell, B. W. 1977: X-ray fluorescence
spectrometry. In: Zussman, J. ed. Physical methods in
determinative mineralogy. 2nd ed. London, Academic
Press. Pp. 201-272.
Norrish, K.; Hutton, T. J. 1969: An accurate X-ray spectrograph
method for the analysis of a wide range of geological
samples. Geochemica et cosmochimica acta 33:431-453.
Palmer, K. 1987: XRF analyses of granitoids and associated rocks
from southern Victoria Land, Antarctica. Victoria
Universityof Wellington Research School of EarthSciences
GeologyBoard of Studiespublication 3.
Palmer, K. 1990: XRF analyses of granitoids and associated rocks,
St Johns Range, south Victoria Land, Antarctica. Victoria
Universityof Wellington Research School of EarthSciences
Geology Board of Studiespublication 5.
Pearce, J. A.; Harris, N. B. W.; Tindle, A. G. 1984: Trace element
discrimination diagrams for the interpretation of granitic
rocks. Journal ofpetrology 25:956-983.
Priestley, R. E. 1914: Glaciology, physiography, stratigraphy and
tectonic geology of south Victoria Land. British Antarctic
Expedition 1907-09, reports on the scientific investigations,
geology 1:244-247.
Skinner, D. N. B. 1983:The granites and two orogenies of Southern
Victoria Land, Antarctica. In: Oliver, R. L.; James, P. R.;
Jago, J. B. ed. Antarctic earth science. Canberra, Australian
Academy of Science and Cambridge, Cambridge University
Press. Pp. 160-163.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-18-320.jpg)
![316 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
Skinner, D. N. B.; Ricker, J. 1968: The geology of the region
between the Mawson and Priestley Glaciers, northern
Victoria Land, Antarctica. Part 1: Basement meta-
sedimentary and igneous rocks. New Zealand journal of
geology and geophysics 11: 1009-1040.
Smillie, R. W. 1989: Granite Harbour Intrusives from the Taylor
Valley and Ferrar Glacier region, southern Victoria Land,
Antarctica. Unpublished M.Sc. thesis, lodged in the Library,
University of Otago, New Zealand.
Smillie, R. W. 1992: Suite subdivision and petrological evolution of
granitoids from the Taylor Valley and Ferrar Glacier region,
south Victoria land. Antarctic science 4: 71-87.
Smith, W. C. 1924: The plutonic and hypabyssal rocks of southern
Victoria Land, Antarctica. BritishAntarctic ("TerraNova ")
Expeditions 1910-13 natural history report geology 1:
167-227.
Streckeisen, A. 1976. To each plutonic rock its proper name. Earth
science reviews 12: 1-33.
Streckeisen, A.; LeMaitre, R. W. 1979: A chemical approximation
to the modal QAPF classification of the igneous rocks.
Neues Jahrbuch fur Mineralogie Abhandlungen 136:
169-206.
Stump, E.; Holloway, J. R.; Borg, S. G.; Lapham, K. E. 1983:
Bowers graben and associated tectonic features across
northern Victoria Land, Antarctica. Nature 304: 334-335.
Talarico, F.; Memmi, I.; Lombardo, B.; Ricci, C. A. 1987:
Thermobarometry of granulite-rocks from the Deep Freeze
Range, North Victoria Land, Antarctica. GeologicalSociety
of Italy memoirs 33: 131-141.
Tulloch, A. J.; Rabone, S. D. C. 1987: Geochemistry of
molybdenum-bearing granodiorite porphyries in west
Nelson with special reference to Eliot Creek, Karamea Bend
and Taipo Spur. In: Proceedings of the 21st annual
conference, New Zealand Branch, Australasian Institute of
Mining and Metallurgy.
Vetter, U.; Tessensohn, F. 1987: S- and I-type granitoids of North
Victoria Land and their inferred geotectonic setting.
GeologischeRundschau 76:233-243.
Weaver, S. D.; Bradshaw, J. D.; Laird, M. G. 1984:Geochemistry of
Cambrian volcanics of the Bowers Supergroup and
implications for early Paleozoic tectonic evolution of northern
Victoria Land, Antarctica. Earthandplanetaryscience letters
68: 128-140.
White, A. J. R.; Chappell, B. W. 1983: Granitoid types and their
distribution in the Lachlan fold belt, south east Australia.In:
Roddick, J. A. ed. Circum Pacific plutonic terranes.
Geological Society of America memoir 159:21-34.
Whitten, E. H. T.; Bornhorst, T. J.; Li, G.; Hicks, D. L.; Beckwith,
J. P. 1987: Suites, subdivision of batholiths and igneous-
rock classification: geological and mathematical concept-
ualization. Americanjournal of science 287: 332-352.
Williamson, B.J.;Downes, H.;Thirlwall,M.F. 1992:The relationship
between crustal magmatic underplating and granite genesis:
an example from the Velay granite complex, Massif Central,
France. Transactions of the Royal Society of Edinburgh
earth sciences 83: 235-245.
Wyborn, L. A. I.; Wyborn, D.; Warren, R. G.; Drummond, B. J.
1992: Proterozoic granite types in Australia: implications
for lower crust composition, structure and evolution.
Transactions of theRoyalSocietyofEdinburghearth sciences
83: 201-209.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/85/Dry-Valleys-Granites-19-320.jpg)
![Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=tnzg20
Download by: [GNS Science] Date: 06 December 2015, At: 17:33
New Zealand Journal of Geology and Geophysics
ISSN: 0028-8306 (Print) 1175-8791 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzg20
Granitoids of the Dry Valleys area, southern
Victoria Land: Geochemistry and evolution along
the early Paleozoic Antarctic Craton margin
Andrew H. Allibone , Simon C. Cox & Robert. W. Smillie
To cite this article: Andrew H. Allibone , Simon C. Cox & Robert. W. Smillie (1993) Granitoids
of the Dry Valleys area, southern Victoria Land: Geochemistry and evolution along the early
Paleozoic Antarctic Craton margin, New Zealand Journal of Geology and Geophysics, 36:3,
299-316, DOI: 10.1080/00288306.1993.9514577
To link to this article: http://dx.doi.org/10.1080/00288306.1993.9514577
Published online: 23 Mar 2010.
Submit your article to this journal
Article views: 80
View related articles
Citing articles: 26 View citing articles](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-1-2048.jpg)
![New Zealand Journal of Geologyand Geophysics,1993, Vol.36: 299-316
0028-8306/93/3603-0299 $2.50/0 © The Royal Society of New Zealand 1993
299
Granitoids ofthe Dry Valleys area, southern Victoria Land:
geochemistry and evolution along the early Paleozoic Antarctic Craton margin
ANDREW H. ALLIBONE
Department of Geology
James Cook University of North Queensland
Townsville, Q4811, Australia*
SIMON C. COX
ROBERT. W. SMILLIE
Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand
*Present address: Etheridge and Henley Geoscience
Consultants, P.O. Box 3778,Manuka, A.C.T 2603, Australia.
Abstract Field relationships and geochemistry indicate
granitoid plutons of the Dry Valleys area comprise at least
three petrogenetically distinct suites.The older Dry Valleys 1a
(DV1a) suite, comprising the Bonney, Catspaw, Denton,
Cavendish, and Wheeler Plutons and hornblende-biotite
orthogneisses, and Dry Valleys 1b (DV1b) suite, comprising
the Hedley, Valhalla, St Johns, Dun, Calkin, and Suess
Plutons,biotite granitoid dikes and biotite orthogneisses, were
emplaced before prominent swarms of Vanda mafic and felsic
dikes. Both the DV1a and DV1b suites are time transgressive,
with older intrusions in each suite being emplaced during the
later stages of deformation of the Koettlitz Group. Younger
granitoids that postdate the majority of the Vanda dikes
include: the Dry Valleys 2 (DV2) suite, comprising the Pearse
and Nibelungen Plutons plus several smaller, unnamed plugs;
and the Harker, Swinford, Orestes, and Brownworth Plutons
with identical field relationships and enclaves but distinct
chemistries.
Chemical characteristics and limited Rb-Sr isotopic dating
indicate plutonism before c. 500 Ma was dominated by the
Cordilleran I-type DV1a suite, inferred to have developed
during melting above a west-dipping subduction zone along
the Antarctic Craton margin. The chemical characteristics of
the DV1b suite indicate large-scale melting of a quartzo-
feldspathic protolith lacking residual plagioclase, but con-
taining refractory garnet. Potential DV1b suite source rocks
include metamorphosed immature sediments, possibly
underplated along the subduction zone associated with DV1a
magmatism, or older granitoid orthogneisses. Major DV1b
plutonism at 490 Ma marks the end of subduction-related
plutonism in southern Victoria Land. Younger DV2 alkali-
calcic, Caledonian I-type plutonism is inferred to have formed
in response to uplift and extension between 480 and 455 Ma.
G92027
Received 2 June 1992; accepted 29 April 1993
Lack of DV2 suite correlatives and Vanda mafic and felsic
dikes in northern Victoria Land suggests significantly
different tectonomagmatic histories along the early Paleozoic
Antarctic Craton margin.
Keywords geochemistry; granitoids; plutons; suites;
petrogenesis; southern Victoria Land; Antarctica; Dry Valleys
INTRODUCTION
Recently, Smillie (1992) proposed a two-fold suite sub-
division of granitoids in the Dry Valleys area of southern
Victoria Land, based on an integrated study of granitoid field
relationships and geochemistry in the Taylor Valley and Ferrar
Glacier area. The older Dry Valleys 1 (DV1) suite comprises
metaluminous, Cordilleran style, calc-alkaline I-type grani-
toids varying in composition from monzodiorite through
quartz-monzodiorite and granodiorite to granite. Granitoids
included in the DV1 suite by Smillie (1992) form two distinct
lithologic varieties: hornblende-biotite, commonly K-feldspar
megacrystic plutons; and equigranular biotite granitoids,
lacking hornblende. The relationship of these two varieties of
granitoid within the DV1 suite is unclear, and geochemistry
discussed by Smillie (1989) indicates that they cannot be
related by simple fractional crystallisation. The younger Dry
Valleys 2 (DV2) suite comprises metaluminous, Caledonian
style, alkali-calcic, I-type granitoids, the compositions of
which range from monzonite through quartz-monzonite to
granite. DV1 granitoids are generally enriched in TiO2,MgO,
CaO, V, Sc, and Cr and depleted in K2O, Rb, Pb, and Zr
relative to DV2 granitoids. Smillie (1992) inferred generation
of the DV1 suite during subduction along the Paleozoic
Antarctic Craton margin, and probable emplacement of the
DV2 suite during a later phase of extension, postdating
subduction.
Analysis of older orthogneisses intercalated with Koettlitz
Group metasediments (Cox & Allibone 1991) indicates that
the two distinct orthogneiss lithologic types (hornblende-
biotite and biotite only) are, with the exception of the Dun
Pluton, chemically identical to younger, relatively unde-
formed hornblende-biotite and biotite granitoids that make up
the DV1 suite. Consequently, emplacement of the DV1 suite
was inferred to span at least the later stages of Koettlitz Group
deformation (Cox 1993). Interrelated plutonism and deform-
ation during emplacement of the regional-scale Bonney
Pluton is discussed by Cox (1993). Garnet-bearing ortho-
gneisses intercalated with Koettlitz Group rocks south of the
study area (Skinner 1983; Findlay 1985) are not discussed
here, and their relationship to the granitoids of the Dry Valleys
area is currently unknown.
In Allibone et al. (1993a, this issue) we presented a map
and general description of the major plutons in the Dry Valleys
area, and a summary of the regional geology (see Fig. 1).An
intrusive history was derived from plutonic field relationships,
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-2-2048.jpg)
![300 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
77.00
McMurdo
Sound -I
•
DV2 and DV2 ? plutons
SP = Swinford Pluton
Hybrid plutons
BP - Brownworth Pluton
Vanda mafic and felsic dikes
Packard Pluton, gabbro
DV1b undeformed plutons
DVIa undeformed plutons
CP = Cavendish Pluton
Gabbroic and dioritic orthogneiss
DV1b orthogneiss
DV1a orthogneiss
Koettlitz Group
Salmon Marble Formation
Hobbs Formation
Scale 10 km
Fig. 1 Inferred basement geology if overlying ice, sediments, moraine, and Ferrar Dolerite were removed to expose the Kukri Erosion
Surface. The DVIa and DVlb plutons (Bonney, Wheeler, Denton, St Johns, Valhalla, and Hedley Plutons) have a consistent northwest
orientation and are cut by northeast-striking younger dikes and the ovoid Pearse, Nibelungen, Brownworth, Orestes, Swinford, and Harker
Plutons.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-3-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 301
and this was correlated with new and earlier radiometric data.
Pluton mapping indicated that hornblende-biotite granitoids
(included in the DV1 suite of Smillie 1992) are generally
ellipsoidal, deep-level, concordant plutons, with northwest-
trending axes parallel to the belts of Koettlitz Group
metasediment. In contrast, equigranular biotite granitoids
(also included in the DV1 suite by Smillie 1992) are similarly
elongate in a northwest direction, but are generally younger
discordant plutons, which intruded by stoping at c. 490 Ma
ago. Swarms of northeast-trending Vanda mafic and felsic
porphyry dikes crosscut these hornblende-biotite and biotite
granitoid plutons. Most of the Vanda mafic and felsic dikes
were subsequently intruded by discordant ellipsoidal-shaped
plutons between 480 and 455 Ma. The occurrence of rare
Vanda mafic and felsic porphyry dikes cutting the younger
discordant plutons, and magmatic microgranitoid enclaves
resembling Vanda dike rocks within these plutons, indicates
emplacement of the Vanda dike swarms continued during and
after the emplacement of the discordant kilometre-scale
granitoid plutons.
This part of our study deals with the geochemistry of
plutons and the evolution of granitoids in southern Victoria
Land. Plutons mapped and described in Allibone et al. (1993a)
are shown in Fig. 1. New analyses of these plutons are
presented (Table 1), and their suite affinities examined.
Unravelling the relationship of hornblende-biotite and biotite
granitoids within the DV1 suite, and their relationship to the
Dun Pluton, is of particular interest. We test the applicability
of Smillie's (1992) DV1/DV2 suite subdivision to the new
plutons mapped and to a wider area of southern Victoria Land.
We outline problems associated with previous granitoid
subdivision schemes applied in southern Victoria Land, in an
attempt to relate our mapping to previous studies.
Similarities between the granitoid geology of the Dry
Valleys area and other parts of the Transantarctic Mountains
as far north as Terra Nova Bay have been inferred since the
early studies of Priestley (1914), Mawson (1916), and Smith
(1924). Subsequent mapping of Larsen Granodiorite (named
from Mt Larsen in northern Victoria Land) and Irizar Granite
(named from Cape Irizar immediately south of Terra Nova
Bay) in northern and southern Victoria Land, by Gunn &
Warren (1962), reinforced the earlier correlations of granitoid
rocks from throughout the Ross Sea sector of the Trans-
antarctic Mountains. The recent publication of major and trace
element analyses of granitoids in each of the terranes of
northern Victoria Land (e.g., Borg et al. 1987; Armienti et al.
1990),combined with the data included in this study, allows a
revision of these earlier correlations between granitoids of
northern and southern Victoria Land. Comparison of the
isotopic character of granitoids in the central Transantarctic
Mountains (Borg et al. 1990) and the Dry Valleys allows a
clarification of the correlation of granitoids and "basement
terranes" in these two areas. Reinterpreted dates (Allibone et
al. 1993a) are used to provide age constraints on the
geochemical, tectonic, and petrogenetic evolution of the
southern Victoria Land margin of the Antarctic Craton during
the early Paleozoic.
GRANITOID GEOCHEMISTRY
Analytical methods
Chemical analysis of granitoid samples was undertaken to
clarify relationships and the petrogenetic evolution of the
various plutons and granitoid dike swarms described in
Allibone et al. (1993a). X-ray fluorescence analyses were
carried out using Sc, Mo, and Au tubes in the University of
Otago Geology Department's Philips PW1410/20 AHP
Spectrometer. Samples were washed, then crushed in a
tungsten carbide swing mill. Major elements were determined
on fused disks using the method of Norrish & Hutton (1969).
Trace elements were determined on 5 g, 32 mm pressed
powder pellets using Mowiol (PVA) binder, and based on the
Norrish & Chappell (1977) procedures. Selected duplicate
samples were analysed by the analytical facility atJames Cook
University of North Queensland to confirm the accuracy of
results.
Analyses are listed in Table 1. In addition to our new
analyses, data from Palmer (1987, 1990), Allibone (1988),
Smillie (1989), Cox (1989), Ellery (1989), and Cox &
Allibone (1991) have been used in this paper. Data collected
for orthogneisses described in Cox & Allibone (1991) are
integrated with data from this and the above studies, requiring
a reinterpretation of orthogneiss petrogenesis.
Normative QAP compositions and DV1/DV2 suite
affinities
Plotting normative compositions of the various plutons and
dikes described in Allibone et al. (1993a) on the Streckeisen
(1976) QAP diagram defines two clear trends (Fig. 2). These
trends are synonymous with the calc-alkaline (DV1) and
alkali-calcic (DV2) suite trends described by Smillie (1992).
The Bonney, Cavendish, Denton, Wheeler, Catspaw, Hedley,
Valhalla, St Johns, Suess, Dun, Calkin, Orestes, and
Brownworth Plutons, various biotite granodiorite and granite
dikes, and hornblende-biotite and biotite orthogneisses plot
along the DV1 trend of Smillie (1992),ranging in composition
from monzodiorite to granite. The Pearse, Rhone, and
Nibelungen Plutons, unnamed quartz-monzonite dikes and
plugs, and all the Vanda felsic porphyry plugs and dikes plot
along the DV2 trend of Smillie (1992),ranging in composition
from monzonite to granite. The Pearse and Nibelungen
Plutons are the first kilometre-scale plutons identified as part
of the DV2 suite.
Several additional features are apparent. Biotite granitoids
(Hedley, Valhalla, Suess, and St Johns Plutons, and unnamed
biotite granite dikes and plugs—solid symbols on Fig. 2)
plotting in the DV1 field of Smillie (1992) form a tightly
constrained trend within the broader DV1 suite trend defined
by the hornblende-biotite granitoids (Bonney, Cavendish,
Denton, Wheeler, and Catspaw Plutons—open symbols on
Fig. 2). This apparent similarity in QAP composition is not
sufficient to confirm a petrogenetic relationship between the
two petrographically distinct granitoid types, within the DV1
suite of Smillie (1992).
The relatively young, discordant Swinford, Orestes,
Brownworth, Pearse, and Nibelungen Plutons, whose
emplacement postdates the majority of the Vanda mafic and
felsic porphyry dikes (Fig. 3), plot in both the DV1 and DV2
suite trends on Fig. 2, defined by Smillie (1992). This implies
the younger, discordant, granitoid plutons do not form a
geochemically coherent suite, despite their similar field
relationships, enclaves, and inferred pluton shapes. Instead, a
more complex petrogenesis is implied, with only the Pearse
and Nibelungen Plutons having field relationships and alkali-
calcic geochemistry analogous to the DV2 suite of Smillie
(1992). Analyses of the Harker Pluton indicate a highly
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-4-2048.jpg)
![Table 1 XRF analyses of granitoids from the Dry Valleys region of southern Victoria Land. Sample numbers with prefix "P"refer to samples lodged in the petrology collection, Institute of Geological
& Nuclear Sciences, Lower Hutt, whereas those with prefix "O"refer to specimens in the University of Otago Geology Department's rock and mineral collection. Major elements are in weight %, trace
elements in ppm. n.d. = not determined, b.d. = below detection.
Sample
OU60757
OU60745
OU60746
OU60749
OU60750
OU60762
OU60763
P49935
OU60760
P49911
OU60752
OU60761
OU61128
OU61136
OU61135
OU61134
OU6H33
OU61118
VU30818
VU30823
VU30821
OU61037
P49933
P50185
P50190
P50161
P50184
OU60557
P49932
P49934
P49935
OU56854
OU56855
P49945
P49962
P49948
P49963
P49964
P49928
P49950
P49949
OU60478
OU60506
OU60509
OU60464
P50178
P50177
P5O18O
P50163
P50169
P50170
P50162
P50171
P50167
Long. E
162-15'
161-40'
161-52'
161-40'
161-42'
162-16'
162-16'
161-56'
162-14'
161-38'
161-44'
162-14'
162-26'
162-31'
162-29'
162-33'
162-40'
162-13'
161-39'
161-40'
161-45'
161°41'
162-01'
161-49'
161-48'
161-36'
161-40'
162-08'
162-03'
162-02'
161-56'
161-56'
162-16'
161-52'
161-37'
161-56'
161-46'
161-43'
161-22'
162-00'
162-00'
162-11'
162°15'
i62°ir
162-16'
161°31'
161-38'
161-15'
161-37'
161-40'
161-39'
161-37'
161-40'
161-39'
Lat. S
77-29.7'
77-31.3'
77-31.1'
77-31.3
77-31.3
77-31.5'
77-31.0'
77-46.9'
77-29.9
77-42.9'
77-31.3'
77-29.9
77-26.4'
77-29.2'
77°28.6'
77-29.0'
77-29.5'
77-27.3'
77-06.8'
77-09.3'
77-07.7'
77°43.4'
77°49.3'
77-42.3'
77-48.0'
77-42.0'
77-40.4'
77-48.0'
77-48.4'
77-49.5'
77°46.9'
77-03.9'
77-48.9'
77-33.4'
77-42.0'
77-33.8'
77-30.9'
77-31.0'
77-49.6'
77-33.6'
77-33.6'
77-42.6'
77-44.0'
77-44.6'
77-42.6'
77-46.0'
77-45.1'
77-45.1'
77-41.9'
77-42.2'
77-42.4'
77-42.0'
77-02.8'
77-41.8'
Pluton
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Bonney
Denton
Denton
Denton
Denton
Denton
Denton
Wheeler
Wheeler
Wheeler
Catspaw
Catspaw
Catspaw
Catspaw
Catspaw
Catspaw
Hedley
Hedley
Hedley
Hedley
Hedley
Hedley
Valhalla
Valhalla
Valhalla
UBGSP
UBGSP
UBGSP
JBGSP
UBGSP
UBGSP
UBGSP
Felsic Porphyry
Felsic Porphyry
Felsic Porphyry
Felsic Porphyry
Felsic Porphyry
UQM, MSP
UQM, MSP
UQM, MSP
UQM, MSP
UQM, MSP
UQM, MSP
SiO2
57.36
62.65
62.88
63.31
63.89
64.38
64.73
65.70
67.34
68.35
70.05
72.56
60.53
64.31
64.73
64.93
70.96
71.38
57.01
63.41
66.13
71.02
71.44
72.31
72.33
72.56
72.78
68.17
70.13
70.40
70.50
71.48
73.58
71.45
71.48
73.58
71.89
72.05
73.71
74.82
75.37
75.55
75.97
64.02
66.47
70.58
71.11
71.74
59.50
60.57
60.73
60.74
63.01
67.83
TiO2
1.05
0.78
0.86
0.83
0.78
0.70
0.66
0.66
0.54
0.55
0.38
0.24
0.89
0.66
0.58
0.63
0.42
0.39
0.47
0.60
0.57
0.31
0.31
0 0
0.28
0.23
0.22
0.30
0.28
0.32
0.29
0.27
0.14
0.24
0.27
0.14
0.18
0.18
0.19
0.08
0.05
0.07
0.07
0.55
0.41
0.29
0.28
0.23
0.79
0.77
0.63
0.66
0.57
0.38
A12O3
19.81
15.93
16.47
16.44
16.14
16.55
16.96
15.83
15.95
14.95
14.76
14.23
17.06
15.13
16.79
16.62
15.40
14.04
19.83
16.76
15.92
14.42
14.29
14.01
13.78
13.96
13.66
16.49
15.59
15.38
15.46
15.41
14.58
14.67
15.41
14.58
15.40
15.45
14.54
13.66
13.46
13.34
13.13
16.17
15.68
14.08
14.14
14.13
17.96
17.58
17.84
17.93
16.93
15.71
Fe2O3T
6.80
5.45
6.27
5.59
5.13
4.99
4.41
4.42
3.76
3.48
2.98
1.68
6.39
5.83
4.45
4.56
2.79
2.63
4.28
4.92
4.51
2.43
2.40
2.07
2.52
2.12
2.37
2.39
1.95
2.18
2.01
2.24
1.32
2.03
2.24
1.32
1.44
1.39
1.38
1.04
0.79
1.15
0.41
5.03
4.02
2.40
2.47
2.31
5.71
5.69
5.23
5.69
4.85
3.30
Fe2O3
0.90
1.43
1.54
0.89
0.91
1.65
1.23
n.d.
0.74
n.d.
0.59
0.71
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.65
0.89
0.74
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.62
n.d.
n.d.
n.d.
0.82
0.18
n.d.
0.82
0.18
n.d.
n.d.
n.d.
n.d.
n.d.
0.21
0.10
0.88
1.18
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
FeO
5.31
3.62
4.26
4.23
3.80
3.01
2.86
n.d.
2.72
n.d.
2.15
0.87
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
3.27
3.63
3.39
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
1.59
n.d.
n.d.
n.d.
1.28
1.03
n.d.
1.28
1.03
n.d.
n.d.
n.d.
n.d.
n.d.
0.85
0.28
3.73
2.56
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
MnO
0 0
0.08
0.09
0.08
0.08
0.06
0.06
00
0.00
0.06
0.05
0.00
0.10
0.10
0.05
ONOe
0.03
0.04
0.10
0.08
0.08
0.04
0.04
0.04
0.05
0.04
0.04
0.03
0.03
0.03
0.03
0.03
0.02
0.03
0.03
0.02
O^ON
ONON
0.03
0.03
0.02
0.04
0.00
0.09
0.07
0.04
0.04
0.04
0.08
0.08
0.09
0.09
oooo
0.06
MgO
2.16
1.84
1.98
1.96
1.65
2.17
1.47
1.56
1.11
1.37
0.88
0.42
2.25
1.94
1.55
1.30
0.79
0.78
2.76
1.79
1.33
0.48
0.49
0.28
0.51
0.32
0.33
0.56
0.46
0.50
0.47
0.48
0.26
0.40
0.48
0.26
0.26
0.27
0.27
0.08
0.04
0.17
0.11
1.24
0.69
0.39
0.34
0.37
1.27
1.21
0.99
0.98
0.90
0.61
CaO
5.65
4.31
4.59
4.32
4.07
4.19
4.46
3.76
3.40
3.26
2.77
1.90
4.87
3.78
3.81
3.84
2.61
2.51
8.14
4.11
3.66
1.83
1.84
1.45
1.71
1.69
1.44
2.95
2.42
2.44
2.34
2.35
1.84
2.41
2.35
1.84
2.04
2.09
1.60
1.21
1.05
1.20
1.46
3.53
2.46
1.71
1.64
1.54
3.83
3.68
3.29
3.35
2.99
2.22
Na2O
4.05
4.29
3.16
3.05
3.17
3.53
3.47
3.89
2.74
3.00
2.51
2.28
3.85
2.99
3.11
3.24
3.88
2.85
4.77
3.59
3.60
3.26
3.52
4.22
3.89
3.38
3.31
3.81
3.62
3.85
3.72
3.73
3.60
3.22
3.73
3.60
4.10
3.94
4.01
3.60
3.59
3.41
2.26
3.59
3.18
2.99
2.89
3.59
4.31
4.25
4.19
4.39
4.26
4.04
K2O
2.61
3.68
3.11
3.68
3.98
2.40
3.14
3.98
4.28
4.27
5.06
5.86
3.03
3.85
4.12
3.78
3.04
4.49
1.76
3.81
3.59
4.90
4.65
4.79
4.48
4.45
4.44
3.27
4.08
3.83
4.07
4.17
4.53
4.43
4.17
4.53
3.78
4.01
4.44
4.42
4.69
4.54
5.83
5.06
5.45
5.59
5.76
5.64
5.03
5.08
5.94
5.50
5.43
5.39
P2O5
0.24
0.27
0.21
0.19
0.19
0.23
0.22
0.15
0.14
0.13
0.09
0.06
0.22
0.16
0.16
0.16
0.10
0.10
0.24
0.18
0.15
0.06
0.07
0.04
0.07
0.04
0.04
0.06
0.06
0.06
0.07
0.06
0.04
0.04
0.06
0.04
0.03
ONON
0.02
0.01
0.00
0.02
0.01
0.22
0.13
0.06
0.06
0.06
0.22
0.20
0.17
0.17
0.15
0.09
LOI
1.03
1.17
0.91
0.99
1.11
1.39
0.74
0.62
0.74
1.14
0.76
0.52
0.37
0.85
0.53
0.51
0.32
0.23
0.96
1.00
0.88
0.52
0.63
0.54
0.50
0.65
0.60
0.68
0.67
1.21
0.80
0.54
0.57
0.59
0.54
0.57
0.51
^5O
0.48
0.35
0.35
0.47
0.54
1.04
1.25
0.87
0.67
1.01
0.95
0.41
0.39
0.43
0.41
0.63
Total
100.25
100.04
100.06
99.97
99.77
100.25
99.98
N00©O
99.74
100.60
100.05
99.66
99.57
99.62
99.89
99.63
100.30
99.46
99.96
99.85
100.04
99.27
99.66
99.97
100.10
99.44
99.24
98.53
99.28
100.20
99.76
100.62
100.37
98.88
100.62
100.37
99.66
99.94
100.70
99.31
99.40
99.87
99.76
100.12
99.53
98.99
99.41
100.70
99.63
99.53
99.49
99.93
99.58
100.30
Ga
30
24
26
21
22
21
19
N0
16
7
16
12
24
21
24
22
23
20
26
23
21
17
19
17
10
15
19
22
12
im
9
16
16
8
15
8
18
^5
15
15
8
19
11
19
19
15
15
18
18
18
16
16
20
16
Rb
124
140
120
156
184
105
100
139
119
138
184
118
154
135
163
123
92
136
101
150
147
180
184
157
185
158
141
95
114
151
111
133
133
121
124
144
134
131
117
173
121
214
147
268
378
257
260
240
132
152
145
131
157
177
Sr
587
479
443
483
422
434
499
485
563
417
469
512
496
437
442
481
542
382
808
420
390
291
2:2
174
210
198
185
674
578
557
653
409
408
445
363
347
631
576
422
344
445
162
546
536
367
261
254
235
896
794
816
716
584
476
Y
19
37
43
26
20
12
17
23
17
24
20
5
38
54
33
27
7
20
17
45
30
22
21
27
25
23
27
17
8
9
9
9
5
9
NI
10
12
7
8
12
9
13
b.d.
40
38
30
27
30
23
17
24
25
33
23
Zr
295
207
233
203
219
165
211
182
199
161
134
104
234
214
211
228
136
152
89
iwi
183
180
183
159
181
162
190
195
172
172
169
182
117
145
122
134
122
124
115
93
145
70
19
272
265
203
194
224
455
472
430
526
404
272
Pb
15
19
19
20
23
14
17
00
21
20
26
22
19
18
23
20
22
22
17
27
23
24
19
27
27
23
25
24
20
im
20
21
24
20
24
23
25
19
25
28
20
38
24
22
24
21
27
30
23
22
30
27
27
28
Th
17
24
17
23
22
13
9
iO
10
9
18
5
20
8
40
24
8
iV
5
iw
20
16
17
14
18
15
16
10
10
ni
7
10
7
6
6
7
b.d.
b.d.
b.d.
b.d.
6
12
b.d.
20
22
22
27
28
7
8
7
7
15
14
NC
8
6
6
6
6
10
6
6
6
5
5
4
9
10
7
6
7
6
b.d.
b.d.
b.d.
5
4
4
5
5
2
3
3
4
3
2
2
4
4
3
5
5
2
3
5
3
2
5
5
4
5
6
5
7
5
5
6
4
Cu
5
2
1
2
2
7
b.d.
2
4
5
b.d.
18
7
b.d.
b.d.
1
1
b.d.
b.d.
b.d.
b.d.
2
2
2
3
3
2
b.d.
3
4
2
b.d.
b.d.
2
1
2
4
3
3
6
2
b.d.
1
7
3
2
2
2
5
65
4
5
3
4
i n
102
72
86
78
75
83
70
67
61
60
44
27
88
87
78
66
60
45
67
77
73
56
46
53
59
84
58
49
43
48
43
39
30
52
42
38
35
^5
33
23
22
28
6
95
60
48
47
50
84
96
79
84
84
63
NP
25
16
18
14
15
18
14
iO
12
12
13
6
24
23
23
22
19
iV
9
iw
17
15
14
15
14
14
16
17
9
9
8
8
8
9
9
10
^O
9
8
13
12
11
b.d.
19
29
16
15
17
18
15
17
17
21
15
V
75
63
73
65
63
74
Mi
52
32
40
24
b.d.
80
64
49
44
27
27
86
57
40
15
18
11
17
13
11
b.d.
11
im
9
16
7
10
9
9
4
b.d.
5
b.d.
6
6
8
26
16
15
14
10
18
18
6
12
14
11
CN
16
12
14
•O
10
21
11
iO
b.d.
10
b.d.
b.d.
26
27
11
iN
9
8
27
iw
13
7
7
4
5
b.d.
4
b.d.
6
6
6
4
b.d.
5
b.d.
4
4
b.d.
4
4
b.d.
5
6
10
7
6
6
4
8
7
6
6
5
5
Ba
557
800
599
947
729
300
847
861
1646
1217
1380
1910
850
1041
935
1021
1152
656
335
807
786
835
794
580
638
513
625
1415
1247
1150
1183
209
903
1044
829
908
1098
1217
832
853
420
269
2135
804
630
658
596
556
2034
2107
2496
1684
1625
999
La
82
52
53
49
62
61
52
49
42
37
32
18
55
22
100
76
33
44
14
41
54
41
: 2
28
47
24
45
50
46
42
35
36
22
43
27
33
10
12
12
6
b.d.
10
6
63
63
65
69
68
61
51
59
74
83
77
Ce
148
102
11
103
126
107
103
95
92
86
81
60
115
57
191
136
60
87
25
76
93
97
93
76
102
67
101
97
104
96
93
61
34
94
78
81
56
62
57
45
34
19
b.d.
120
122
132
141
139
125
116
147
152
167
154
Pr
10
12
14
12
14
14
13
iO
8
10
9
7
13
8
19
iN
5
5
n.d.
n.d.
n.d.
7
8
9
10
8
10
n.d.
8
6
7
n.d.
n.d.
10
9
7
7
8
b.d.
b.d.
b.d.
n.d.
n.d.
n.d.
n.d.
13
13
17
13
6
10
18
17
15
NH
44
35
48
34
45
30
32
25
26
24
21
11
47
34
73
49
20
28
n.d.
n.d.
n.d.
28
22
23
31
15
30
27
19
im
15
n.d.
n.d.
23
14
19
b.d.
7
b.d.
b.d.
b.d.
b.d.
b.d.
44
48
46
44
48
42
b.d.
44
54
61
15
^
«t
S
o
oo
5"
1Q
1
f
5
|u>
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-5-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica
Fig. 2 Normative QAP composi-
tions of analyses of the various
plutons plotted after Streckeisen
(1976). Compositions of the DV1
and DV2 suites from Smillie
(1992) areplotted for comparison.
Granitoids mapped during this
study show an identical two-fold
subdivision into theDV1 andDV2
suites of Smillie (1992). Biotite
granitoids within the DV1 suite
(solid symbols) form a narrow,
well-defined trend within the
broader DV1 suite field of Smillie
(1992). Data are from this study,
Palmer (1987, 1990), and Ellery
(1989).
303
v i O N © " ^ •**•**—NO"^•**•** — N O m
I « » DC VI -H t—CT>l/l t^ © (N
© N o o w - i w - i u - i r - oot--©
r r - r - r N p r - v i m m m r j i n
© © © q o © o — © o © o
© © © © © d d © d o © ' ©
8SSS58SSSS3S
© © ' © d o d o © © © © ©
q q q q
c c c c
d d d d d d o d © © © ©
|^j ^ j ^ j r ^ pQ
OO n *—> — oo
§§iSS
Q60:AP40
quartz-monzonitel M quarU-monzodiorite
Tnonrartom6
A65:P35
X Marker Pluton
v Swinford Pluton
4- Pearse Pluton
O Brownworth Pluton
• Biotite granite dikes
M Quartz-monzonite sills
+ Felsic porphyry plugs
A35:P65 A10:P90
• Orestes Pluton
A Valhalla Pluton
T Hedley Pluton
• Suess Pluton
4 St. Johns Pluton
o Catspaw Pluton
A Denton Pluton
V Bonney Pluton
.,/2>Bonney Pluton (Smillie1992)
1 D V 1 s u i t e
(Smilli
e 1992)
O D V 2 suite (Smillie1992)
evolved composition, which plots at the intersection ofthe
DV1 andDV2 trends (Fig. 2).Further analysis is required to
define thesuite affinity ofthe Harker Pluton.
Relationship ofhornblende-biotite and biotite granitoids
within theDV1 suite ofSmillie (1992), and the"Dun
Type" orthogneiss ofCox &Allibone (1991)
In many ofthe discriminant and variation diagrams presented
below, hornblende-biotite granitoids of the DV1 suite
(hornblende-biotite orthogneisses, Bonney, Denton,
Cavendish, Wheeler, andCatspaw Plutons) display distinctly
different evolutionary trends from biotite granitoids ofthe
DV1 suite (Hedley, Valhalla, Suess, and St Johns Plutons,
biotite orthogneisses including theDunandCalkin Plutons,
and biotite granite dikes). This implies that theDV1 suite,as
defined by Smillie (1992), comprises two,petrogenetically
distinct suites. Thedistinct geochemistry of thehornblende-
biotite andbiotite granitoids previously included in the DV1
suite bySmillie (1992) isconsistent with the different styleof
emplacement of the major hornblende-biotite granitoid
plutons (Bonney, Denton, Cavendish, Wheeler) and biotite
granitoid plutons (Hedley, Valhalla, StJohns, Suess) outlined
in Allibone et al. (1993a). Accordingly, in the following
discussion, the hornblende-biotite granitoids are referred to as
DVla suite granitoids, andbiotite granitoids as DVlb suite
granitoids. TheDVla and DVlb suites are petrogenetically
distinct and unlikely to be derived from the same source
material. They are not subdivisions of a larger overallDV1
suite. DV1 is retained inthename of each suite to emphasise
the partly coeval, time transgressive nature of the DVla and
DVlb suites, inferred from field relationships outlined in
Allibone etal. (1993a) and illustrated inFig.3.
Harker variation diagrams (Fig. 4) indicate DVlb biotite
granitoids are enriched in A12O3, Na2O, and Sr relative to
DVla hornblende-biotite granitoids. Both types define
distinctly different trends on the variation diagrams. The
slopes of the A12O3 versus SiO2, Na2O versus SiO2 and Sr
versus SiO2 trends for the DVlb biotite granitoids are
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-6-2048.jpg)
![304 New Zealand Journal of Geology and Geophysics, 1993,Vol. 36
migmatite development
—isoclinal folding
upright folding about
NNW trending axes
KOETTLITZ GROUP
hornblende-biotite
orthogneiss
. Bonney |
i Denton 1
Wheeler .,
Cavendish .
.Catspaw,
DRY VALLEYS 1a
(DV1a) SUITE
Dun
Calkin
biotlte orthogneiss
Medley
Valha
St.Johns
DRY VALLEYS 1b
(DV1b) SUITE
VANDA MAFIC DIKES
I Orestes .
Brownworth
STRONG DRY VALLEYS 2 CHARACTER
DRY VALLEYS 2
(DV2) SUITE
• qtz monzonite.
'dikes & plugs' Pearse
t Nibelungen
H
oldest
5 8 6 ' ' 4 9 0
AGE Ma NOT TOSCALE
486 I 477 I
youngest
Fig. 3 The inferred relative timing of emplacement of the various plutons,dike swarms,and granitoid suites mapped. Emplacement ofthe
DVla andDVlb suites overlaps withthe later stages of deformation and migmatitedevelopment inthe Koettlitz Group.Emplacement ofthe
DV2 suite postdates emplacement of the DVla and DVlb suites, and the majority of the VandaDikes.
especially steep relative to the DVla hornblende-biotite
granitoids. DVlb granitoids are also highly enriched in Ba
relative to DVla granitoids (Fig. 4), but values for biotite
orthogneisses show a wider scatter, possibly as a result of
incipient to extensive migmatite development. DVlb grani-
toids and orthogneisses are extremely depleted in Nb (not
plotted here) and Y, and Rb, K2O, MgO, Cr, V, and Th (not
plotted here) to a lesser extent, relative to DVla granitoids
(Fig. 4; Cox & Allibone 1991). Na2O/K2O ratios (Fig. 5) of
DVlb granitoids and orthogneisses are also consistently
higher than those of DVla hornblende-biotite granitoids.
Chondrite normalised LREE profiles are similar for both the
DVla and DVlb granitoids (Fig. 6), but more evolved DVlb
granitoids are characterised by lower absolute LREE con-
centrations.
Analyses of the "Dun Type" orthogneisses (Cox &
Allibone 1991) appear to form the less evolved extension of
the DVlb biotite granitoid trends, implying the orthogneiss
Dun Pluton is also part of the DVlb suite. Structural
relationships outlined in Allibone et al. (1991) and Cox &
Allibone (1991) imply that emplacement of the Dun Pluton
and other biotite orthogneisses occurred before Fj, isoclinal
folding of the Koettlitz Group (Fig. 3). The simplest
interpretation, consistent with the structural relationships and
geochemistry of the Dun Pluton, is that emplacement of the
DVlb suite spans a significant part of the structural-
metamorphic history of the Koettlitz Group. Radiometric
dating (discussed in Allibone et al. 1993a) indicates an age
difference anywhere between a few million years and 120Ma
separating emplacement of the orthogneiss Dun Pluton and the
major DVlb Hedley, Valhalla, St Johns, and Suess Plutons.
While the shorter time span is perhaps easier to rationalise
with the inferred time scale of tectonomagmatic events,
emplacement of small, petrogenetically associated DVlb suite
intrusives over 120 Ma may imply a relatively stable
tectonomagmatic situation for this length of time.
Fig.4 Major andtraceelement Harkerdiagrams illustrating thedifferences andsimilarities inthechemistry ofthevarious granitoidplutons
andsuites intheDryValleys area.HarkerdiagramsindicatethattheDVla hornblende-biotite granitoids andtheDVlbbiotitegranitoidsform
two,distinct,evolutionary trends."Dun-Type"biotiteorthogneisses (Cox&Allibone 1991)represent themost unevolved oftheDVlbbiotite
granitoids, rather than a separate petrogenetic suite. The Orestes Pluton exhibits DVlb geochemistry, despite havingfieldrelationships and
enclavestypicalofDV2granitoids,whiletheHarker andSwinford Plutons show close affinities withthe DV2suite.TheBrownworthPluton
showsmixed DVla+b andDV2chemical character. Dataarefrom this study, Palmer (1987),Allibone (1988),Ellery (1989), Smillie(1989),
and Cox &Allibone(1991).
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-7-2048.jpg)
![400
300
200
100
1000
Ift
55 60 65 70 75 80 55 60 65 70 75 80 55 60 65 70 75 80 55 60 65 70 75 80
•9
O
55 60 65 70 75 80
55 60 65 70 75 80
SiO2
© DVIa granitoid • DV1b granitoid
A DVIaorthogneiss * DVIborthogneiss
55 60 65 70 75
2500
55 60 65 70 75
SiO2
x DV2 granitoid • Brownworth
* Harker
e Swinford
30
25
20
15
10
5
0
Cr
ft a
©© ©
© © a ©
© «© © ©
o
ft xas ©
© ©o©»
X
X L
xaA
e e©
55 60 65 70 75 80
55 60 65 70
SiO2
I'
55 60 65 70 75 80
55 60 65 70 75 80
SiO2
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-8-2048.jpg)
![306 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
o DV1 a granitoid
A DVIaorthogneiss
• DV1b granitoid
A DVIborthogneiss
x DV2 granitoid
a Orestes
• Brownworth
* Harker
© Swinford
Fig. 5 Na2O versus K2O plot of granitoid analyses. The DVla
hornblende-biotite granitoids, DVlb biotite granitoids, and DV2
suite quartz-monzonites and granites each define a distinct
evolutionary trend.DVla granitoids arecharacterised by arelatively
shallow negative slope,unlike the steeper negative slope defined by
themoresodicDVlbbiotitegranitoids.TheK2Ocontent oftheDV2
suite appears independent of the Na2Ocontent. Fields of S-typeand
I-type granitoids, after White & Chappell (1983), are plotted for
comparison.Dataarefrom this study,Palmer (1987,1990),Allibone
(1988),Ellery (1989), Smillie (1989), and Cox &Allibone (1991).
Field relationships, petrographic characteristics, and
geochemical data all support the subdivision of the DV1 suite
as defined by Smillie (1992) into two petrogenetically distinct
and unrelated suites. These are the DVla suite consisting of
hornblende-biotite granitoids and a DVlb suite consisting of
biotite granitoids. Hornblende-biotite and biotite ortho-
gneisses described by Cox & Allibone (1991) are inferred to
be integral parts of the DVla and DVlb suites, respectively.
The structural relationships of individual intrusions within
both the DVla and DVlb suites indicates emplacement of
both suites spans at least the later stages of deformation and
metamorphism of the older Koettlitz Group. Consequently,
both the DVla and DVlb suites are inferred to be time
transgressive. Each suite represents a continuum of intrusions,
rather than a distinct, separate, plutonic event at a specific
geologic time (Fig. 3).Thepartly coeval emplacement of these
two unrelated granitoid suites indicates coeval melting of
distinct protoliths.
Comparison of the DV2 suite with the DVla and DVlb
suites
Analyses of the Pearse Pluton and unnamed quartz-monzonite
dikes, plugs, and sills indicate geochemical characteristics
analogous to the DV2 suite as defined by Smillie (1992). The
Pearse Pluton and the unnamed quartz-monzonite dikes,
plugs, and sills both have high K2O, Rb, Pb, and Zr contents
relative to the DVla and DVlb suites (Fig.4,5). Analyses also
show the DV2 suite intrusions are depleted in MgO, CaO, V,
and Cr relative to DVla granitoids, although DV2 suite MgO,
V, and Cr contents are similar to DVlb rocks. In addition, less
evolved samples of the Pearse Pluton and the unnamed quartz-
monzonite dikes are highly enriched in Ba (up to 2500 ppm)
and Sr (up to 900 ppm) (Fig. 4). In both the Ba and Sr versus
SiO2 variation diagrams (Fig. 4) the DV2 suite granitoids
exhibit a steep negative slope, parallel to that defined by the
DVlb suite, but at lower SiO2 values, clearly illustrating the
different evolutionary trends of each suite. Ba and Sr contents
of the DVla suite are lower, with Ba/SiO2 and Sr/SiO2
variation diagrams having a shallower slope than for the DVlb
and DV2 suites, again clearly illustrating the different
evolutionary trends of each suite. The DV2 suite is enriched in
LREE relative to both the DVla and DVlb suites (Fig. 6).
Despite overlap between DVla and DV2 suite Na2O, A12O3,
and Y contents, and DVlb and DV2MgO,Cr, and V contents,
it is apparent that, when the geochemical data are combined
with field relationships, three, rather than two, distinct
petrogenetic suites, as proposed by Smillie (1992), are present
in the Dry Valleys area.
Suite affinities of the Swinford, Brownworth, Orestes,
and Harker Plutons
Field relationships indicate that these four plutons have similar
ages and intrusive styles as the granitoids included in the DV2
suite (Allibone et al. 1993a, fig. 3). Felsic porphyry enclaves
identical to the Vanda dikes, present in each of these plutons,
are also typical of the DV2 suite granitoids described by
Smillie (1992). Analyses of these four plutons are plotted in
Fig. 4, 5, and 6. They indicate the chemistry of these four
plutons deviates from the chemistry characteristic of the DV2
suite as outlined in Smillie (1992).
Analyses of the Swinford Pluton indicate a composition
generally consistent with DV2 suite characteristics. Only the
relatively low K2O and Rb contents of the Swinford Pluton are
inconsistent with its DV2 field relationships and felsic
porphyry enclave suite.The Harker Pluton is the most evolved
granitoid studied. In many variation diagrams (Fig. 4,5,7) the
Harker Pluton plots at the intersection of trends defined by two
or three of the DVla, DVlb, or DV2 suites. Consequently, the
chemistry of the Harker Pluton is generally consistent with it
being part of the DV2 suite, with only the low K2O, Rb, and
Ba contents of the least evolved samples deviating from the
chemical characteristics of the DV2 suite.
The Brownworth and Orestes Plutons exhibit few
chemical features in common with the DV2 suite as defined by
Smillie (1992). This is despite having identical field relation-
ships and enclaves. The chemistry of the Orestes Pluton is
analogous to the older DVlb suite biotite granodiorites and
granites, rather than the DV2 suite. This is consistent with the
lack of hornblende in the Orestes Pluton, an important feature
of the DVlb suite, and unlike the other younger discordant
plutons. The field relationships of the Vanda dikes and the
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-9-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 307
Fig. 6 Chondrite normalised
LREE contents of the granitoid
samples. DV2 suite granitoids are
enriched in LREE relative to DV1a
and DVlb suite granitoids. Small
peaks in each profile probably
reflect the analytical procedure
rather than real differences in the
relative LREE concentrations.
1000r
800
600
400
200
100
80
60
4 0
20
Dry Valleys 1asuite Dry Valleys 1 b suite Dry Valleys 2 suite
+ Orestes Pluton
—-Brownworth Pluton
La Cs Pr Nd La Ce Pr Nd La Ce Pr Nd
Orestes Pluton indicate that the Orestes Pluton is probably the
oldest of the relatively young discordant plutons, with field
relationships and enclaves analogous to the DV2 suite defined
by Smillie (1992). This is consistent with the conflicting
chemistry, field relationships, and enclaves of the Orestes
Pluton, which indicate features in common with both the
DVlb and DV2 suite.
Whether the Brownworth, Orestes, Harker, and Swinford
Plutons are included in the DV2 suite depends on how the
DV2 suite is defined. If field relationships and enclave types
are emphasised in the suite definition, then all four plutons
would be included. Alternatively, if geochemistry is
emphasised, then the Orestes Pluton at least would be included
in the DVlb suite, while the Harker, Swinford, and
Brownworth Plutons would not form part of any chemically
coherent suite. This is analogous to the situation outlined by
Whitten et al. (1987) who suggested numerous different suites
can be defined depending on the combination of criteria
selected. The lack of chemical coherence within these younger
discordant plutons with Vanda felsic porphyry enclaves
indicates amore complex petrogenesis than can beresolved by
a simple suite-style approach. Throughout the remainder of
this paper, only those plutons with field relationships and
chemical characteristics consistent with the original defini-
tion of the DV2 suite are referred to as DV2 suite granitoids.
The Brownworth, Orestes, Swinford, and Harker Plutons are
referred to individually, or as granitoids with apparently
unique combinations of field relationships and chemical
features. This approach is consistent with the implied complex
petrogenesis of the younger granitoids, and is preferable to
squeezing all these plutons into a single suite or defining
multiple suites to accommodate individual plutons.
1000
500 •
200
100 -
50
:Rb
•
•
„—•
o
1 1
Syn-collisional
Volcanic arc
/
1 *
Intraplate
10 20 50 100
Nb+Y
o DV1a
• DV1b
x DV2
• Orestes Pluton
• Brownworth Pluton
+ Harker Pluton
- Swinford Pluton
Fig. 7 Rb versus Nb+Y plot illustrating the depletion of the DV lb
suite biotite granitoids and Orestes Pluton in Nb and Y relative to the
DVla hornblende-biotite granitoids and the DV2 suite. The higher
Rb content of the evolved DV2 suite granitoids relative to the DVla
and DVlb suite granitoids is also apparent. Tectonic setting
discriminant fields, after Pearce et al. (1984), are plotted for
comparison. Data are from this study, Palmer (1987,1990), Allibone
(1988), Smillie (1989), and Ellery (1989).
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-10-2048.jpg)
![308 New Zealand Journal of Geology and Geophysics, 1993,Vol. 36
CORRELATION OF PLUTONS AND SUITES WITH
PREVIOUSLY DESCRIBED GRANITOID UNITS IN
SOUTHERN VICTORIA LAND
Many previous workers in southern Victoria Land preferred to
discuss the granitoids of the Dry Valleys area as large-scale
units. These units are inferred here to be similar to suites of
individual plutons, although they were commonly not defined
as such (e.g., Gunn &Warren 1962;McKelvey & Webb 1962;
Allen & Gibson 1962; Haskell et al. 1965a; Skinner 1983;
Findlay 1985,1991). These large-scale units or suites include:
the Pre-tectonic Gneisses, Larsen Granodiorite, and Irizar
Granite initially proposed by Gunn & Warren (1962);
Olympus Granite Gneiss, Dias Granite, Theseus Granodiorite,
and Vida Granite initially proposed by McKelvey & Webb
(1962); and the Kukri Hills, Larsen, and Victoria Intrusive
Groups proposed by Findlay (1985). Some of these large-scale
units were mapped throughout southern Victoria Land and the
Wilson Terrane of northern Victoria Land (e.g., Larsen
Granodiorite, Irizar Granite in Gunn & Warren (1962) and
Skinner & Ricker (1968)). The internal makeup of these larger
scale units is not discussed by many workers, although Gunn
& Warren (1962) noted that the Irizar Granite defined by them
consists of a number of separate plutons, whereas Skinner
(1983) noted that the Larsen Granodiorite is a convenient
name for a family of similar plutons.
Sufficient detailed mapping has now been completed to
allow an attempt at unravelling the relationships between suite
nomenclatural schemes used by previous workers and this
study. This discussion is an addition to the similar discussion
in Smillie (1992), made necessary by the recognition of the
DVla and DVlb suites here.
The larger concordant plutons included in the DVla suite
here were initially included in the Pre-tectonic Gneisses of
Gunn & Warren (1962) and the Dias Granite and Olympus
Granite Gneiss of McKelvey & Webb (1962) and Allen &
Gibson (1962). The relatively small leucocratic Catspaw
Pluton, also included in the DVla suite here, has previously
been described as Irizar Granite by Haskell et al. (1965a).
Subsequent workers have described the major plutons within
the DVla suite as Larsen Granodiorite (Haskell et al. 1965a;
Skinner & Ricker 1968; Skinner 1983) or members of the
Larsen Intrusive Group (Findlay 1985, 1991). Gneissose
margins of the Bonney, Wheeler, Cavendish, and Denton
Plutons were included in the Larsen Intrusive Group by
Findlay (1985), but hornblende-biotite orthogneisses, inferred
here to be genetically associated with these plutons, were
included in the Kukri Hills Group by Findlay (1985).
Plutons included in the DVlb suite here were initially
described as grey granite by, amongst others, Ferrar (1907)
and Mawson (1916), and later named Larsen Granodiorite by
Gunn & Warren (1962). However, subsequent workers (e.g.,
Haskell et al. 1965a; Skinner &Ricker 1968) applied the name
Larsen Granodiorite to plutons here included in the DVla
suite. These and subsequent workers have included DVlb
suite in either the Vida Granite (Allen & Gibson 1962), Irizar
Granite (Haskell et al. 1965a), or Victoria Intrusive Group
(Findlay 1985).
The DV2 suite and plutons with distinct chemistries, but
identical field relationships, were initially described as Irizar
Granite (Gunn & Warren 1962;Haskell et al. 1965a) and Vida
Granite (McKelvey & Webb 1962; Allen & Gibson 1962),
along with other plutons here included in the DVla and DVlb
suites. Most recently, Findlay (1985) included rocks, here
described aspart of the Brownworth Pluton, in the Briggs Hills
Granodiorite, a suite scale subunit of the Larsen Intrusive
Group. Other rocks that form part of the Pearse Pluton were
not assigned by Findlay (1985) to any particular unit.
Many of the individual plutons from each of the three
suites of granitoids identified here have in the past been
assigned to all the major granitoid units used by previous
workers. This reflects the superficial similarity of many of the
plutons in each of the three suites. Geochemical analysis
during this study has sometimes indicated that granitoids
initially assumed to be related on the basis of similar hand-
specimen characteristics are unrelated plutons forming parts
of genetically distinct suites (e.g., Catspaw and Pearse
Plutons). Furthermore, the DVla and DVlb suites are inferred
to be time transgressive, with emplacement of constituent
plutons spanning at least the later stages of deformation in the
adjacent Koettlitz Group (Cox & Allibone 1991). The time-
transgressive nature of the suites defined here differs from the
approach of previous workers who have attempted to
distinguish the older granitoids partly on the basis of their
inferred timing of emplacement relative to folding phases
within the Koettlitz Group (e.g., Skinner 1983;Findlay 1985,
1991). This earlier approach tends to mask the genetic
relationships of the various plutons and has the potential to
separate genetically associated granitoids emplaced at differ-
ent times into different suites, and combine genetically distinct
plutons emplaced at the same time in the same suite, thereby
confusing the petrogenetic interpretation of these granitoids.
As a result of this study, we suggest that future workers
record the shape and internal characteristics of individual
plutons, rather than just summarise their observations by
interpreting larger scale units, as has occurred in the past.
Chemical analyses can then be related back to individual
plutons with clearly defined field relationships, rather than
interpeted suites that may contain unrelated plutons. Given the
repeated inclusion of genetically unrelated plutons in the
following previously defined, larger scale granitoid units, we
would recommend that they be abandoned or confined to
plutons in their respective type areas: Olympus Granite
Gneiss, Larsen Granodiorite, Irizar Granite, Vida Granite,
Dias Granite, Briggs Hills Granodiorite, Larsen Intrusive
Group, Victoria Intrusive Group, Kukri Hills Group, and
Theseus Granodiorite.
CORRELATION WITH NORTHERN
VICTORIA LAND
Background geology
Several recent papers provide sufficient analyses of granitoids
(Borg et al. 1987; Vetter & Tessensohn 1987; Ghezzo et al.
1987; Armienti et al. 1990) from northern Victoria Land to
allow a comparison with the chemistry of granitoids from the
Dry Valleys area, and thereby test correlations made by earlier
workers (e.g., Gunn & Warren 1962; Skinner & Ricker 1968).
Potential correlatives of granitoids from the Dry Valleys area
are those in the westernmost Wilson Terrane of northern
Victoria Land (Stump et al. 1983). Bowers Terrane island arc
tholeiites (Weaver et al. 1984; Bradshaw et al. 1985)
juxtaposed against the eastern margin of the Wilson Terrane
are considered to be allochthonous to the Antarctic Craton
margin. Bradshaw et al. (1985) suggested accretion of the
Bowers Terrane against the Antarctic Craton margin c. 500
Ma ago, postdating emplacement of Cambro-Ordovician
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-11-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 309
Q"
40 60
ANOR
80 100
o DV1a • DV1b x DV2
Mt Abbott Intrusives (MAI)
I ' I I J South Victoria Land Intrusives (SVLI)
Fig. 8 Normative compositions of Dry Valley granitoids plotted in
terms of the Q' and ANOR parameters after Streckeisen & LeMaitre
(1979). Evolutionary trends of the southern Victoria Intrusives
(SVLI) and the Mt Abbott Intrusives (MAI) of northern Victoria
Land, after Armienti et al. (1990), are plotted for comparison. DV1 a
and DVlb granitoids exhibit a similar trend to the SVLI of northern
Victoria Land. The DV2 suite is characterised by a more "syenitic"
evolutionary trend than either the SVLI or MAI.
sg, syenogranite; mg, monzogranite; gr, granodiorite; ton, tonalite;
qs, quartz syenite; qm, quartz monzonite; qmd, quartz monzodiorite;
qd, quartz diorite; sy, syenite; mo, monzonite; md, monzodiorite; di,
diorite.
"Granite Harbour Intrusives" in northern Victoria Land, but
predating emplacement of the Devonian Admiralty Intrusives
in all terranes of northern Victoria Land.
Both Borg et al. (1987) and Vetter & Tessensohn (1987)
mapped dominantly two-mica S-type granites in the western
part of the Wilson Terrane and gabbroic to granitic I-type
granitoids in the eastern part of the Wilson Terrane. An active
continental margin setting for the observed plutonism was
inferred by both Borg et al. (1987) and Vetter & Tessensohn
(1987), with the chemical data of Borg et al. (1987) suggesting
increasing involvement of metasedimentary material in the
granitoid source rocks towards the western part of the Wilson
Terrane. Presumably, subduction ceased immediately to the
east of the Wilson Terrane at c. 500 Ma with accretion of the
adjacent Bowers Terrane.
Unlike Borg et al. (1987) and Vetter &Tessensohn (1987),
Ghezzo et al. (1987) noted significant amounts of I-type
granitoid cropping out in the southern and western parts of the
Wilson Terrane, indicating that the distribution of S-type and
I-type granitoids is more complex than suggested by Borg et
al. (1987) or Vetter & Tessensohn (1987). Armienti et al.
(1990) identified two batholiths comprising three distinct I-
type plutonic complexes of differing petrographic and
chemical character in the Wilson Terrane of northern Victoria
Land. In the southern part of northern Victoria Land, Armienti
et al. (1990) described the "South Victoria Land Intrusives"
(SVLI), which were inferred to be the northern extension of
granitoids cropping out in the Dry Valleys area. The SVLI
range in composition from diorite to leucogranite and include
the granitoids of the Mt Larsen and Cape Irizar areas, which
have previously been correlated with granitoids in southern
Victoria Land (Larsen Granodiorite, Irizar Granite of Gunn &
Warren 1962 and Skinner & Ricker 1968). To the north and
east of the SVLI, the Wilson Terrane is intruded by the
gabbroic to monzogranitic Deep Freeze Range Intrusives
(DFRI) and the syenogranite-dominated Mt Abbott Intrusives
(MAI) (Armienti et al. 1990). The DFRI and MAI in the north
and east of the Wilson Terrane (Lantermann Terrane of
Bradshaw et al. 1985) are separated from the SVLI in the south
and west of the Wilson Terrane (Daniels Terrane of Bradshaw
et al. 1985) by the Priestley Fault (Armienti et al. 1990),
equivalent to the Soza Fault of (Bradshaw et al. 1985) and the
Rennick-Aviator Line of Grew et al. (1984). The Priestley or
Soza Fault corresponds to achange inthe metamorphic history
of the older metasedimentary rocks (Grew et al. 1984). Grew
& Sandiford (1984, 1985) indicate schists hosting the DFRI
east of the Soza/Priestley Fault contain assemblages indic-
ative of metamorphic pressures in excess of 6 kbar. Grew et
al. (1984) and Vetter & Tessensohn (1987) described assem-
blages indicative of peak metamorphic pressures of c. 4 kbar
west of the Priestley/Soza Fault in rocks that host the SVLI.
Correlation
The apparent petrographic similarity of the SVLI and
granitoids of the Dry Valleys area, long recognised by
previous workers (e.g., Gunn & Warren 1962), indicates the
SVLI are the most likely correlatives in northern Victoria
Land of the Dry Valleys granitoids. The MAI are also
compared with granitoids from the Dry Valleys, as their
syenogranite composition is similar to the DV2 suite.
Normative compositions of granitoids from the Dry Valleys
are plotted and compared to the SVLI and MAI of northern
Victoria Land (Armienti et al. 1990) in Fig. 8 (after
Streckeisen & LeMaitre 1979). The DVla and DVlb suites
show a similar evolutionary trend to the SVLI of northern
Victoria Land, ranging in composition from monzodiorite and
quartz-diorite through quartz-monzodiorite and granodiorite,
to monzogranite. However, the evolutionary trend of the DV2
suite from syenite and monzonite through quartz-syenite to
syenogranite is distinctly more "syenitic" than the evolu-
tionary trends of either the SVLI or MAI. Therefore, the DV2
suite does not appear to have any geochemical counterparts in
either the MAI or the SVLI of northern Victoria Land.
Granitoids from the Dry Valleys area are compared further
with the SVLI and MAI of northern Victoria Land in Harker
diagrams (Fig. 9). The Harker diagrams suggest a similarity
between the less evolved parts of the SVLI and the DVla suite
of the Dry Valleys area. However, the SVLI analyses of
Armienti et al. (1990) show significant scatter into the DVlb
field, which is consistent with the presence of biotite
granitoids in the SVLI (Armienti et al. 1990) similar to the
DVlb suite. So-called "Irizar Type" evolved granitoids,
described by Armienti et al. (1990), within the SVLI do not
show any affinity with the DV2 suite from the Dry Valleys
area, despite their similar appearance in hand specimen.
Rather, granitoids from the Cape Irizar area of northern
Victoria Land appear similar in chemical character to the
evolved DVla suite Catspaw Pluton. Comparison of the MAI
with the Dry Valleys granitoids indicates a weak similarity to
the DV2 suite, although evolutionary trends on the Harker
diagrams do not generally overlap.
The limited data available indicate that the DVla suite in
the Dry Valleys area could be a southern extension of the
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-12-2048.jpg)
![310 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
3 •
65_._ 70
SiO2
CaO
:X
•
. +•••-.
200-
100•
40
Volcanic arc granitoid intraplate
To ' 20 40 60 i6<
Nb+Y
C ! ? DVIaSuite
C t3 DV1b Suite
•:
:• DV2 Suite
+
o
South Victoria Land Intrusives (SVLI)
Ml Abbott Intrusives (MAI)
Fig. 9 Harker diagrams com-
paring the evolutionary trends of
the DVla, DVlb, and DV2 suites
in the Dry Valleys area (from Fig.
4) with the SVLI and MAI of
northern Victoria Land. Analyses
of the SVLI and MAI are taken
from Armienti et al. (1990). The
SVLI shows similar geochemical
character to both the DVla and
DVlb suites. The DV2 suite
exhibits different evolutionary
trends to either the SVLI or MAI,
albeit with more similarities to the
MAI than theSVLI.
SVLI, with both "Larsen Type" and "Irizar Type" granitoids
of Armienti et al. (1990) being represented by the DVla suite.
However, further data are required to assess whether the
DV1b suite also occurs in the SVLI of northern Victoria Land.
No direct correlative of the DV2 suite appears to be present in
the SVLI, as the "Irizar Type" granitoids of Armienti et al.
(1990) display different evolutionary trends. This is an
important conclusion because granitoids here included in the
DV2 suite in the Dry Valleys area have previously been
widely correlated with the granitoids of the Cape Irizar
area in northern Victoria Land (e.g., Gunn & Warren 1962;
Haskell et al. 1965a; Skinner & Ricker 1968; Skinner 1983).
Furthermore, Vanda mafic and felsic dike swarms also appear
to be absent from the SVLI of northern Victoria Land.
Correlation of the SVLI of northern Victoria Land with the
older granitoids of the Dry Valleys area is compatible with the
metamorphic history of the host metasedimentary rocks.
Koettlitz Group metasediments of the Dry Valleys area were
inferred to have been metamorphosed at 700-750°C and 4-5
kbars (Murphy 1971;Allibone 1992; Cox 1992), similar to the
metamorphic history inferred for the host rocks of the SVLI
west of the Soza/Priestley Fault or Rennick-Aviator Line, but
distinct from that inferred for the host rocks of the DFRI, east
of the Soza/Priestley Fault (Grew & Sandiford 1984, 1985;
Grew et al. 1984; Vetter & Tessensohn 1987; Talarico et al.
1987).
CORRELATION WITH THE CENTRAL
TRANSANTARCTIC MOUNTAINS
McGregor (1965) and Haskell et al. (1965b) mapped a variety
of granitoids including inferred pre-, syn-, and post-tectonic
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-13-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 311
plutons within the Queen Maud Batholith of the central
Transantarctic Mountains, south of the Dry Valleys. Sub-
sequently, Borg (1983) noted a similar variety of granitoids,
and subdivided these granitoids into S-types, more common in
the western part of the Queen Maud Batholith adjacent to the
Antarctic Craton margin, and I-types dominating the eastern
part of the batholith. Haskell et al. (1965b) initially noted the
petrographic similarity of some rocks in the Queen Maud
Batholith and granitoids of the Dry Valleys area. Based on an
interpretation of radiometric dates and this apparent petro-
graphic similarity, Skinner (1983) suggested a correlation
between the Carlyon Granodiorite (an integral part of the
Queen Maud Batholith) and Larsen Granodiorite of the Dry
Valleys area, here interpreted as partly equivalent to the
DVla suite. However, Findlay (1991) noted that the Carlyon
Granodiorite contains hypersthene and muscovite, unlike the
Larsen Granodiorite/Intrusive Group, and questioned this
correlation.
More recently, Borg et al. (1990) described regional
variations in the isotopic character of granitoids between the
Nimrod Glacier and Gabbro Hills in the central Transantarctic
Mountains, south of the Dry Valleys area. Cambrian-
Ordovician granitoids in the westernmost Miller Range that
intrude Precambrian metasediments forming the easternmost
part of the Antarctic Craton are characterised by 87
Sr/86
Sr; in
the range 0.73243-0.74174. Cambrian-Ordovician granitoids
further to the east, between the Marsh Glacier and Shackleton
Glacier, are characterised by lower initial 87
Sr/86
Sr; ratios in
the range 0.70684-0.71906. Granitoids in the Gabbro Hills
area east of the Shackleton Glacier are characterised by the
lowest initial 87
Sr/86
Sri ratios of 0.70446-O.70589. These
variations in isotopic character are consistent with the west-
east change from S-type to I-type granitoids previously
described by Borg (1983).
Lack of published whole-rock analyses from granitoids of
the Queen Maud Batholith prevents direct comparison with
the chemistry of the DVla, DVlb, and DV2 suites of the Dry
Valleys area. The lack of S-type granitoids in the Dry Valleys
area is a fundamental difference, although similar rocks may
be present beneath the ice cap to the west. Available Sr-isotope
analyses from the Dry Valleys area (see discussion in Allibone
et al. 1993a), including granitoids from the DVla, DVlb, and
DV2 suites, exhibit a similar range of 87
Sr/86
Sr; to the
granitoids cropping out between the Marsh and Shackleton
Glaciers in the central Transantarctic Mountains.
Borg et al. (1990) inferred the area between the Marsh and
Shackleton Glaciers, referred to as the Beardmore Micro-
continent, is allochthonous to the east Antarctic Craton, on the
basis of the isotopic character of the Cambrian-Ordovician
granitoids. Stratigraphic and intrusive relationships constrain
the timing of accretion of the Beardmore Microcontinent to
between 760 and 550 Ma (Borg et al. 1990). Granitoids
cropping out between the Marsh and Shackleton Glaciers,
with Sr-isotopic compositions similar to the Dry Valleys
granitoids, were inferred to be derived from thinned Pre-
cambrian continental crust (Borg et al. 1990). Additional Sr,
Nd, and Pb isotopic data are required to adequately describe
the granitoids of the Dry Valleys area and assess whether the
crustal and tectonic model developed for the central Trans-
antarctic Mountains by Borg et al. (1990) is applicable to the
Dry Valleys area. The presence of at least three granitoid
suites in the Dry Valleys area suggests considerable subtle
complexity not yet recognised in the central Transantarctic
Mountains area, or perhaps not present.
PETROGENESIS, SOURCE CRITERIA, AND
TECTONIC SETTING OF THE DVla, DVlb, AND
DV2 SUITES
Smillie (1992) inferred a subduction-related, continental arc
setting associated with generation and emplacement of the
DV1 suite, based on the characteristics of the DVla Bonney
Pluton. Recognition of two fundamentally distinct DVla and
DVlb suites, initially included in the DV1 suite of Smillie
(1992), requires some reassessment of the source rocks and
tectonic setting associated with emplacement of these rocks.
Smillie (1992) inferred the younger DV2 suite was emplaced
during postsubduction extension as a result of melting of I-
type crustal material. It is possible that this occurred in
response to emplacement of mantle-derived mafic rocks,
perhaps represented by the shoshonites described by Keiller
(1991), which crop out extensively throughout southern
Victoria Land. Recognition of the geochemical complexity
and conflicting chemical characteristics of the younger
granitoids, with similar relative ages and enclave suites to
those defined as members of the DV2 suite by Smillie (1992),
requires reassessment of the petrogenesis of these younger
granitoids as well.
Source criteria and petrogenesis of DVla and DVlb
suites
Smillie (1992) clearly demonstrated the I-type characteristics
of the DVla Bonney Pluton. This interpretation was based on
the hornblende-clinopyroxene bearing assemblages, abun-
dance of mafic enclaves, and relatively metaluminous, calcic,
and sodic composition compared with S-type granitoids. The
essentially identical characteristics of the other DVla
granitoids described by Allibone et al. (1993a, b) and Cox &
Allibone (1991) are also consistent with an I-type classi-
fication. Rb, Sr, Na2O, K2O,and A12O3contents of these rocks
are similar to those documented in Cordilleran I-type
granitoids developed in volcanic arcs along continental
margins (e.g., Atherton & Sanderson 1985).
The DVlb suite is characterised by several features not
typical of continental arc granitoids. These include the
restricted compositional range, between 64 and 76 wt% SiO2,
the extreme enrichment in Sr and to a lesser extent Na2O and
A12C<3, and the extreme depletion in Y and Nb, while
maintaining LREE contents comparable to typical I-type
granitoids. This set of petrographic and geochemical features
is not typical of either S-type or I-type granitoids as described
by White &Chappell (1983).DVlb suite Sr,Na2O, andA12O3
contents are considerably higher and exhibit steeper negative
correlations with SiO2 than typical Cordilleran I-type
granitoids, similar to the DVla suite rocks (e.g., Atherton &
Sanderson 1985), although these features are partly analogous
to the chemistry of tonalites and trondhjemites (e.g., Manduca
et al. 1992; Barnes et al. 1992).
The high Sr content of the DVlb granitoids implies
advanced melting of a dominantly quartzofeldspathic source
in which plagioclase is not a residual phase. Alternatively, it
may indicate a lesser degree of partial melting in a source rich
in refractory minerals such as garnet and pyroxene, again
where plagioclase is not a residual phase (e.g., Anderson &
Cullers 1987, 1990; Tulloch & Rabone 1987; Manduca et al.
1992; Wyborn et al. 1992). Advanced melting of a quartzo-
feldspathic protolith is consistent with the overall grano-
dioritic composition of the DVlb suite. The extreme deple-
tion in Y implies the presence of a refractory phase that
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-14-2048.jpg)
![312 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
preferentially incorporates Y (and HREE) in the residual
material, such as garnet. Lack of significant garnet within all
but the most evolved DVlb granitoids would be consistent
with only relatively minor residual garnet in a dominantly
quartzofeldspathic protolith. Garnet present in the most
evolved DVlb granitoids is inferred to have crystallised from
the melt during emplacement, since the most evolved DVlb
suite granitoids tend towards peraluminous compositions
(also reflected in the presence of muscovite accompanying
garnet).
The source material for the DVlb suite must also be
capable of producing a granitoid melt with an initial 87
Sr/86
Sr
ratio around 0.708-0.709. This initial 87
Sr/86
Sr ratio is
significantly higher than tonalitic and trondhjemitic rocks
with superficially similar Sr, Na2O, and AI2O3 enriched
chemistries, that are commonly inferred to have been derived
by either partial melting, or fractional crystallisation of
primitive basaltic material. Furthermore, the DVlb suite is
significantly enriched in K2O and Rb compared to tonalitic
and trondhjemitic rocks, which is reflected in the granodiorite
and granite compositions. The restricted range of quartzo-
feldspathic compositions implies the DVlb suite was derived
from a similar relatively felsic, homogeneous source, rather
than by fractional crystallisation of more mafic melts, which
would produce dioritic and monzodioritic or tonalitic
intrusives as well.
Potential source rocks that could account for the character-
istics of the DVlb suite include older, garnet-bearing,
metaluminous granitoids or relatively immature meta-
sediments. Melting of more mature sediments with pelitic
compositions would give rise to granitoids with more typical
S-type features, including peraluminous compositions and
higher initial 87
Sr/86
Sr ratios. However, immature sediments
containing relatively little material derived from old Archean
and early Proterozoic sources could produce granitoid melts
with bulk rock compositions and isotopic characteristics
analogous to the DVlb suite. In order to account for the Y
depletion, some garnet would need to be present in this
metasedimentary protolith.
Garnet and two-mica granodiorites and granites with
chemistries similar to the DVlb suite have recently been
described by Anderson & Cullers (1990) from the lower plate
of the Whipple Mountain Metamorphic Core Complex. The
grosssular-rich garnet compositions in these granitoids
indicate crystallisation at pressures between 7.5 and 9 kbars,
indicative of arelatively deep level of emplacement. Anderson
& Cullers (1990) inferred that these granitoids were derived
during partial melting of calcic greywackes, derived from a
continental margin volcanic arc, metamorphosed to refractory
garnet and omphacite-bearing, eclogite fades assemblages.
Partial melting of garnet-bearing, eclogite facies rocks was
invoked to explain the unusually high Sr content and depleted
Y content of these granitoids. This hypothesis is consistent
with petrologic evidence of a deep level of emplacement.
Similar hypotheses involving partial melting at extreme
depths have been invoked to explain the analogous chemistry
of granitoids described by Wyborn et al. (1992), Norman et al.
(1992), and Williamson et al. (1992). However, none of these
other studies describe direct petrologic evidence of a deep
level during granitoid emplacement.
An analogous model could be postulated to account for the
geochemical characteristics of the DVlb suite. Volcanogenic
sediment underplated along the west-dipping subduction zone
inferred to have been associated with DVla plutonism is a
potential source for the DVlb suite. However, unlike the
Whipple Mountain Metamorphic Core Complex granitoids,
there is no direct evidence of a deep level of emplacement or
generation for DVlb plutonism. Instead, most of the geologic
evidence appears to contradict such a model. Clinopyroxene
grains in the DVlb suite Dun Pluton have Fe-rich salitic
compositions, without any trace of Al or Na that would be
expected if they had crystallised under relatively high
pressures. Field evidence indicates that the younger DVlb
plutons are discordant, with irregular intrusion breccias
developed along their margins. This contrasts with the
concordant margins typical of granitoids emplaced at deeper
levels. Any inference that the DVlb suite was derived from
melting of sediments or plutonic rocks metamorphosed to
eclogite facies assemblages would have to be based solely on
the Sr-enriched and Y-depleted chemistry of these rocks,
rather than a combination of petrologic and chemical data
as in the Whipple Mountain Metamorphic Core Complex
(Anderson & Cullers 1990). Garnet development in meta-
morphic rocks over a wide range of temperatures, pressures,
and whole-rock compositions indicates that these chemical
features need not be indicative of partial melting at extreme
depths, provided all available plagioclase in the protolith is
consumed during partial melting.
What is clear is that the DVlb protolith was characterised
by a distinct composition and mineral assemblage compared
with the partly coeval DVla suite, which implies coeval
melting of distinct source rocks in different parts of the crust
and possibly upper mantle.
Petrogenesis of the DV2 suite and the Harker, Swinford,
Orestes, and Brownworth Plutons
The different chemical characteristics of these individual
plutons and the DV2 suite require explanation. Each of these
individual plutons and others included in the DV2 suite are
inferred to have broadly similar ages, and all contain
microgranitoid enclaves identical to the Vanda felsic porphyry
dikes. Given these similar field relationships, a correspond-
ing similar, coherent geochemistry would be expected.
Variation in the chemistry of these granitoids may be caused
by several processes or combinations of processes. These
could include melting of a chemically inhomogeneous source,
different amounts of contamination possibly by older DVla
and DVlb granitoids, or subtle differences in the amount of
fractional crystallisation within individual plutons during
emplacement.
Any model proposed to explain the characteristics of these
plutons, which involves contamination of an "end member"
DV2 melt, comparable to the least evolved parts of the Pearse
or Rhone Plutons (Smillie 1992), must account for the
selective changes in the concentration of only some of the
chemical parameters relative to the inferred "end member"
DV2 melt. For example, the chemistry of the Harker and
Swinford Plutons is largely consistent with the DV2 suite
except for the low K2O and Rb contents. This indicates any
contaminant in these two plutons has only affected these two
parameters. In contrast, the Orestes Pluton exhibits chemical
characteristics almost completely consistent with the DVlb
suite. Furthermore, the lack of widespread, partially assim-
ilated xenoliths in any of these younger plutons is difficult to
reconcile with a contamination hypothesis.
Alternatively, intrusion of DV2 suite granitoids may have
been accompanied by partial melting of older DVla and
DVlb suite granitoids, which were emplaced at deeper levels
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-15-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 313
than those currently exposed in the Dry Valleys area. In this
hypothesis, little interaction is inferred between the melt that
crystallised to form the DV2 suite plutons and other melts that
produced the Harker, Swinford, Orestes, and Brownworth
Plutons. This is distinct from the contamination hypothesis,
where incorporation of xenolithic material during emplace-
ment is the process controlling the chemistry of the resulting
granitoid plutons.
Liquid-crystal fractionation, particularly in more felsic
granitoids, is widely postulated as the cause of significant
enrichment or depletion of granites in some incompatible trace
elements (e.g., Champion & Chappell 1992). At high SiO2
contents, relatively small amounts of crystal fractionation can
markedly affect the content of some trace elements. The
evolved compositions of the Orestes and Harker Plutons, in
particular, are consistent with liquid-crystal fractionation
being an important control on the chemistry of these
granitoids. Similar suites of granitoids with incoherent
chemistries are mentioned by Wyborn et al. (1992), who
referred to these rocks as "melt-rich" granitoids as opposed to
"restite-rich" granitoids. Wyborn et al. (1992) suggested the
distinctive compositions of individual plutons reflects the
melt-rich character of these intrusions during their emplace-
ment. This allows each intrusion to independently undergo
crystal-liquid fractionation, resulting in distinct chemistries
developing, despite similar ages and field relationships. A
similar hypothesis could be invoked to explain the different
chemistries of the younger granitoid plutons in the Dry
Valleys area. This would imply that all the younger plutons are
derived from the same source, and are closely related, which is
consistent with their field relationships.
The relative importance of crystal-liquid fractionation and
melting of an inhomogeneous source cannot be currently
determined. Each is potentially capable of explaining the
variations in chemisty between these younger granitoids.
Tectonic synthesis: evolving plutonism along the early
Paleozoic Antarctic Craton margin
Field relationships, geochemistry, and radiometric dating
indicate several marked changes in the nature of granitoid
plutonism in the Dry Valleys area. These changes in the
character of granitoid plutonism are inferred to reflect
concurrent changes in the tectonic setting of the Cambrian-
Ordovician Antarctic Craton margin. The earliest plutonism is
dominated by the DVla suite with concurrent, but minor,
DVlb plutonism. Given the similarity of the DVla suite to
granitoids generated along continental margin arcs, a
subduction setting is inferred at this time. Concurrent
emplacement of small DVlb suite intrusions indicates minor
melting of a distinctly different protolith. This protolith may
have been small amounts of underplated metasediment
derived from the arc associated with DVla plutonism.
Termination of DVla suite plutonism was followed by
emplacement of all the major DVlb suite plutons (Hedley,
Valhalla, Suess, St Johns), marking a distinct change in the
nature of granitoid plutonism along the early Ordovician
Antarctic Craton margin. Radiometric dating of the St Johns
Pluton indicates emplacement of this pulse of DVlb plutons
occurred at 490 ± 14 Ma (Allibone et al. 1993a). The cause of
this marked change in the style and chemistry of granitoid
plutonism is unclear. However, it coincides with the inferred
timing of accretion of the Bowers Terrane along the Antarctic
Craton margin in northern Victoria Land (Bradshaw et al.
1985) at c. 500 Ma. Cessation of DVla plutonism in southern
Victoria Land before c. 490 Ma, could indicate either a
cessation of subduction altogether, or a radical change in the
style of subduction. Cessation of subduction at this time in
southern Victoria Land would be consistent with a similar
accretion event. The pulse of DVlb plutonism emplaced at
c. 490 Ma may reflect increased amounts of sediment
underplated during such an accretion event, although this
inference is highly speculative. Such an accreted terrane may
now form the seafloor east of the current southern Victoria
Land coast, along strike from the Bowers Terrane in northern
Victoria Land. Clasts of volcanics and low-grade meta-
sediment occurring in basal Devonian conglomerates of the
overlying Beacon Supergroup throughout the Olympus and St
Johns Ranges (Allibone et al. 1993b) have no obvious
provenance in present-day southern Victoria Land. These
rocks may be derived from this postulated allochthonous
terrane.
Emplacement of the DVlb suite was followed within 10
Ma or less by intrusion of the Vanda mafic dikes and
associated felsic porphyry dikes. Keiller (1991) concluded that
these were generated at the base of the crust by interaction of a
mantle melt and a crustal component. Subsequent evolution
was dominated by fractional crystallisation of alkali felspar.
Field relationships indicate emplacement of the dikes was
essentially contemporaneous with the beginning of DV2
alkali-calcic, Caledonian I-type magmatism. Analogous
granitoids elsewhere are inferred to have developed in some
type of extensional setting unrelated to subduction (Smillie
1992). Correlations inferred here suggest these later post-
subduction granitoids and dikes do not occur in northern
Victoria Land, indicating different Cambrian-Ordovician
tectonomagmatic histories along the length of the Paleozoic
Antarctic Craton margin between c. 486 and 450 Ma.
SUMMARY AND CONCLUSIONS
Chemical analyses of granitoids emplaced before the prom-
inent Vanda mafic and felsic dike swarms in southern Victoria
Land, indicate the existence of the distinct Dry Valleys la
(DVla) and Dry Valleys lb (DVlb) suites. The DVla suite
includes the batholithic-scale Bonney Pluton and at least four
other major plutons of hornblende-biotite granitoid, as well as
hornblende-biotite orthogneisses described by Cox &
Allibone (1991). The DVlb suite includes several large
plutons of biotite granodiorite and granite, and younger
plugs of biotite granite (partly equivalent to the Theseus
Granodiorite of McKelvey & Webb 1962), as well as biotite
orthogneisses and the "Dun Type" orthogneisses of Cox &
Allibone (1991). Field relationships indicate that emplace-
ment of the older orthogneisses in both suites overlap, but the
majority of DVla plutons, including the Bonney Pluton,
predate emplacement of a major pulse of DVlb plutons.
Radiometric dating indicates emplacement of the DVla and
DVlb suites occurred before c. 490 Ma (Allibone et al.l993a).
Younger granitoids emplaced after the majority of the
Vanda mafic and felsic dike swarms, include the large Pearse
and Nibelungen Plutons and other smaller bodies with
chemistries analogous to the DV2 suite of Smillie (1992).
Other relatively young granitoids (e.g., Orestes, Brownworth,
Harker, and Swinford Plutons) were emplaced at the same
time as the DV2 suite granitoids and contain identical felsic
porphyry enclaves but they have variable geochemistries and
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-16-2048.jpg)
![314 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
do not form part of a chemically coherent suite. DV2
granitoids and other plutons with analogous field relationships
and enclaves, but different chemistries, were emplaced
between c. 486 and 450 Ma.
Comparison of granitoids from the Dry Valleys area with
the "South Victoria Land Intrusives" of northern Victoria
Land described in Armienti et al. (1990) indicates potential
correlatives of the DVla and possibly DVlb suites. DV2 suite
rocks from the Dry Valleys area, previously correlated with
the evolved granitoids of Cape Irizar, are distinctly more
monzonitic to syenitic in character. The only potential
correlative of the Cape Irizar granitoids so far mapped in
southern Victoria Land is the evolved DVla Catspaw Pluton.
Sparse Sr-isotope data suggest granites of the Dry Valleys area
are possible correlatives of granitoids cropping out between
the Shackleton and Marsh Glaciers in the central Trans-
antarctic Mountains (Borg et al. 1990).
The geochemistry and abundance of mafic enclaves in the
DVla suite plutons is typical of Cordilleran style I-type
granitoids, and they are inferred to have developed above a
subduction zone along an active continental margin. Chemical
characteristics of the relatively leucocratic DVlb suite are
more unusual. In particular, the very high Sr, A12O3 and Na2O
contents, coupled with extremely low Y contents, indicate a
source region lacking residual plagioclase, but containing
garnet. Partly analogous granitoids elsewhere are inferred to
have been derived from an eclogite fades protolith. However,
no direct geologic evidence exists of such a source for the
DVlb suite,other than the similar chemistry. The source of the
DVlb suite granitoids is unclear although they may be derived
from underplated volcanogenic sediments derived from the
arc associated with DVla suite plutonism. The marked pulse
of DVlb suite plutons corresponds to the timing of accretion
of the Bowers Terrane in northern Victoria Land at c. 500 Ma
and may reflect a similar accretion event in southern Victoria
Land. The younger DV2 suite granitoids are analogous to
Caledonian style I-type granitoids thought to be related to
uplift and extension rather than subduction processes.
The following speculative sequence of events is proposed
to account for changes in the characteristics of granitoids
along the Cambrian-Ordovician Antarctic Craton margin.
Subduction-related Cordilleran style magmatism dominated
before c. 500 Ma. At c. 500-490 Ma, Cordilleran type
plutonism ceased and was replaced by a short pulse of
DVlb plutonism characterised by Sr, Na and Al enriched, and
Y depleted geochemistry, suggesting partial melting of garnet-
bearing source rocks lacking residual plagioclase. These
unusual granitoids may have been derived from sediment
underplated along the subduction zone associated with
Cordilleran plutonism. This pulse of DVlb suite plutonism
may have developed in response to collision between an
allochthonous terrane and the Antarctic Craton margin,
marking the end of subduction-related plutonism. Later DV2
and related younger plutons are inferred to have been
emplaced during postcollision uplift and extension, from
c. 486 to 455 Ma.
ACKNOWLEDGMENTS
The authors thank D. Craw and R. D. Johnstone for their discussion
and critical comments that considerably improved this paper. P. J.
Forsyth, R. D.Johnstone, and M. Hunter are thanked for maintaining
a sense of humour while crushing rocks and making XRF disks. S.
Ness and A. Chappell are thanked for access to XRF facilities at
JCU. In this paper we have drawn conclusions from data and
observations of K. Palmer, I. J. Graham, I. G. Keiller, S. Ellery, R. J.
Sewell, and I. M. Turnbull in addition to our own. Reviews by S. D.
Weaver, J. D. Bradshaw, and R. H. Findlay resulted in considerable
improvement to the paper. Fieldwork was made possible by The
Ross Dependency Research Committee, Antarctic Division (DSIR)
and VXE-6 squadron (U.S. Navy).
REFERENCES
Allen, A. D.; Gibson, G. W. 1962: Geological investigations in
southern Victoria Land, Antarctica. Part 6: Outline of the
geology of the Victoria Valley region. New Zealand journal
of geology and geophysics 5: 234-242.
Allibone, A. H. 1988: Koettlitz Group meta-sediments and
intercalated orthogneisses from the mid Taylor Valley and
Ferrar Glacier regions. Unpublished M.Sc. thesis, lodged in
the Library, University of Otago, New Zealand.
Allibone, A. H. 1992: Low pressure/high temperature
metamorphism of Koettlitz Group schists in the Taylor
Valley and Ferrar Glacier area, South Victoria Land,
Antarctica. New Zealandjournal of geology andgeophysics
35: 115-127.
Allibone, A. H.; Forsyth, P. J.; Sewell, R. J.; Turnbull, I. M.;
Bradshaw, M. A. 1991: Geology of the Thundergut area,
southern Victoria Land, Antarctica. 1:50 000 miscell-
aneous series map 21 (with supplementary text).
Wellington, New Zealand. Geology and Geophysics
Division, Department of Scientific and Industrial Research.
Allibone, A. H.; Cox, S. C.; Graham, I. J.; Smillie, R. W.; Johnstone,
R. D.; Ellery, S. G.; Palmer, K. 1993a: Granitoids of the Dry
Valleys region, southern Victoria Land, Antarctica: plutons,
field relationships, and isotopic dating.New Zealandjournal
of geology and geophysics 36: 281-297 (this issue).
Allibone, A. H.; Heron, D. W.; Forsyth, P. J.; Turnbull, I. M. 1993b:
Geology of the St Johns Range, southern Victoria Land,
Antarctica. 1: 50 000 miscellaneous series map (with
supplementary text). Lower Hutt, New Zealand. Institute of
Geological and Nuclear Sciences.
Anderson, J. L.; Cullers, R. L. 1987: Crust-enriched, mantle-derived
tonalites in the early Proterozoic Penokean Orogeny of
Wisconsin. Journal of geology 95: 139-154.
Anderson, J. L.; Cullers, R. L. 1990:Middle to upper crustal plutonic
construction of a magmatic arc; An example from the
Whipple Mountains Metamorphic Core Complex.
Geological Society of America memoir 174:47-69.
Armienti, P.; Ghezzo, C.; Innocenti, F.; Manetti, P.; Rocchi, S.;
Tonarini, S. 1990: Isotope geochemistry and petrology of
granitoid suites from the Granite Harbour Intrusives of the
Wilson Terrane, North Victoria Land, Antarctica. European
journal of mineralogy 2: 103-123.
Atherton, M. P.; Sanderson, L. M. 1985:The chemical variation and
evolution of the super-units of the segmented Coastal
Batholith. In: Pitcher, W. S.; Atherton, M. P.; Cobbing, E. J.;
Beckinsale, R. D. ed. Magmatism at a plate edge: The
Peruvian Andes. Glasgow, Blackie & Son Ltd. Pp. 208-227.
Barnes, C. G.; Barnes, M. A.; Kistler, R. W. 1992: Petrology of the
Caribou Mountain Pluton, Klamath Mountains, California.
Jounal ofpetrology 33: 95-124.
Borg, S. G. 1983: Petrology and geochemistry of the Queen Maud
batholith, central Transantarctic Mountains with
implications for the Ross Orogeny. In: Oliver, R. L.; James,
P. R.; Jago, J. B. ed. Antarctic earth science. Canberra,
Australian Academy of Science and Cambridge, Cambridge
University Press. Pp. 165-169.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-17-2048.jpg)
![Allibone et al.—Geochemistry of granitoids, Antarctica 315
Borg, S. G.; Stump, E.; Chappell, B. W.; McCulloch, M. T.;
Wyborn, D.; Armstrong, R. L.; Holloway, J. R. 1987:
Granitoids of northern Victoria Land, Antarctica: impli-
cations of chemical and isotopic variations to regional
crustal structure and tectonics. American journal of science
287: 127-169.
Borg, S. G.; DePaolo, D. J.; Smith, B. M. 1990: Isotopic structure
and tectonics of the central Transantarctic Mountains.
Journal of geophysical research 95: 6647-6667.
Bradshaw, J. D.; Weaver, S. D.; Laird, M. G. 1985: Suspect
terranes and Cambrian tectonics in northern Victoria Land,
Antarctica. In: Howell, D. G. ed. Tectonostratigraphic
terranes in the Circum Pacific region. Circum-Pacific
Councilfor Energy and Mineral Resources—earthscience
series 1: 493-514.
Champion, D. C.; Chappell, B. W. 1992: Petrogenesis of felsic I-
type granites: an example from northern Queensland.
Transactions of the Royal Society of Edinburgh earth
sciences 83: 115-126.
Cox, S. C. 1989: Gneiss geology—a structural perspective of
foliated granitoids and their host rocks in the Wright Valley,
South Victoria Land, Antarctica. Unpublished M.Sc. thesis,
lodged in the Library, University of Otago, New Zealand.
Cox, S. C. 1992: Garnet-biotite geothermometry of Koettlitz Group
metasediments, Wright Valley, South Victoria Land,
Antarctica. New Zealandjournal of geology and geophysics
35: 29-40.
Cox, S. C. 1993: Inter-related plutonism and deformation in South
Victoria Land, Antarctica. Geological magazine 130: 1-14.
Cox, S. C.; Allibone, A. H. 1991: Petrogenesis of granitoid
orthogneisses from the Dry Valleys region, south Victoria
Land, Antarctica. Antarctic science 3: 405-417.
Ellery, S. G. 1989: Lower Wright geology. Unpublished M.Sc.
thesis, lodged in the Library, University of Otago, New
Zealand.
Ferrar, H. T. 1907: Report on the field geology of the region
explored during the "Discovery" Antarctic expedition.
National Antarctic Expedition 1901-04 natural history
reports 1: 1-100.
Findlay, R. H. 1985: The Granite Harbour Intrusive Complex in
McMurdo Sound: progress and problems. New Zealand
Antarctic record 6 (3): 10-22.
Findlay, R. H. 1991: Antarctica. In: Nairn, A. E. ed. The Phan-
erozoic of the World, Vol. A, The Palaeozoic. Amsterdam,
Elsevier Publishing Company. Pp. 335-421.
Ghezzo, C.; Baldelli, C.; Biagini, L.; Carmignani, L.; Di Vincenzo,
G.; Gosso, G.; Lelli, A.; Lombardo, B.; Montrasio, A.;
Pertusati, P. C.; Salvini, F. 1987: Granitoids from the David
Galcier-Aviator Glacier segment of the Transantarctic
Mountains, North Victoria Land, Antarctica. Geological
Society of Italy memoirs 33: 143-159.
Grew, E. S.; Sandiford, M. 1984: A staurolite-talc assemblage in
tourmaline-phlogopite-chlorite schist from northern
Victoria Land, Antarctica, and its petrogenetic significance.
Contributions to mineralogy and petrology 87: 337-350.
Grew, E. S.; Sandiford, M. 1985: Staurolite in a garnet-hornblende-
biotite schist from the Lantermann Range, northern Victoria
Land, Antarctica. Neues Jahrbuch fur Mineralogie
Monatschefte, Heft. 9: 396-410.
Grew, E. S.; Kleinschmidt, G.; Schubert, W. 1984: Contrasting
metamorphic belts in northern Victoria Land, Antarctica.
GeologischesJahrbuch. B 60:253-263.
Gunn, B. M.; Warren, G. 1962: Geology of Victoria Land between
the Mawson and Mulock Glaciers, Antarctica. NewZealand
GeologicalSurvey bulletin 71.
Haskell, T. R.; Kennett, J. P.; Prebble, W. M.; Smith, G.; Willis,
I. A. G. 1965a: The geology of the middle and lower Taylor
Valley of southern Victoria Land, Antarctica. Transactions
of the Royal Society of New Zealand 2: 169-186.
Haskell, T. R.; Kennett, J. P.; Prebble, W. M. 1965b: The geology of
the Brown Hills and Darwin Mountains, southern Victoria
Land, Antarctica. Transactions of the Royal Society of New
Zealand 2: 231-248.
Keiller, I. G. 1991: Wright dikes—a geochemical study of dike-
forming rock types within the Wright Valley, Southern
Victoria Land, Antarctica. Unpublished M.Sc. thesis,
lodged in the Library, University of Otago, New Zealand.
McGregor, V. R. 1965: Geology of the area between the Axel
Heiberg and Shackleton Glaciers, Queen Maud Range,
Antarctica. Part 1: Basement complex, structure and glacial
geology. New Zealandjournal of geology and geophysics8:
314-343.
McKelvey, B. C.; Webb, P. N. 1962: Geological investigations in
Southern Victoria Land, Antarctica. Part 3: Geology of
Wright Valley. New Zealand journal of geology and
geophysics 5: 143-162.
Manduca, C. A.; Silver, L. T.; Taylor, H. P. 1992: 87
Sr/86
Sr and18
O/
16
O isotopic systematics and geochemistry of granitoid
plutons across a steeply-dipping boundary between con-
trasting lithospheric blocks in western Idaho.Contributions
to mineralogy andpetrology 109:355-372.
Mawson, D. 1916: Petrology of rock collections from the mainland
of southern Victoria Land. Report of the British Antarctic
Expedition 1907-09 geology 1:201-237.
Murphy, D. J. 1971:The petrology and deformational history of the
basement complex, Wright Valley, Antarctica, with special
reference to the origin of augen gneisses. Unpublished Ph.D.
thesis, lodged in the library, University of Wyoming. 114p.
Norman, M. D.; Leeman, W. P.; Mertzman, S. A. 1992:Granites and
rhyolites from the northwestern USA: temporal variation in
magmatic processes and relations to tectonic setting.
Transactions of the Royal Society of Edinburgh earth
sciences 83: 71-81.
Norrish, K.; Chappell, B. W. 1977: X-ray fluorescence
spectrometry. In: Zussman, J. ed. Physical methods in
determinative mineralogy. 2nd ed. London, Academic
Press. Pp. 201-272.
Norrish, K.; Hutton, T. J. 1969: An accurate X-ray spectrograph
method for the analysis of a wide range of geological
samples. Geochemica et cosmochimica acta 33:431-453.
Palmer, K. 1987: XRF analyses of granitoids and associated rocks
from southern Victoria Land, Antarctica. Victoria
Universityof Wellington Research School of EarthSciences
GeologyBoard of Studiespublication 3.
Palmer, K. 1990: XRF analyses of granitoids and associated rocks,
St Johns Range, south Victoria Land, Antarctica. Victoria
Universityof Wellington Research School of EarthSciences
Geology Board of Studiespublication 5.
Pearce, J. A.; Harris, N. B. W.; Tindle, A. G. 1984: Trace element
discrimination diagrams for the interpretation of granitic
rocks. Journal ofpetrology 25:956-983.
Priestley, R. E. 1914: Glaciology, physiography, stratigraphy and
tectonic geology of south Victoria Land. British Antarctic
Expedition 1907-09, reports on the scientific investigations,
geology 1:244-247.
Skinner, D. N. B. 1983:The granites and two orogenies of Southern
Victoria Land, Antarctica. In: Oliver, R. L.; James, P. R.;
Jago, J. B. ed. Antarctic earth science. Canberra, Australian
Academy of Science and Cambridge, Cambridge University
Press. Pp. 160-163.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-18-2048.jpg)
![316 New Zealand Journal of Geology and Geophysics, 1993, Vol. 36
Skinner, D. N. B.; Ricker, J. 1968: The geology of the region
between the Mawson and Priestley Glaciers, northern
Victoria Land, Antarctica. Part 1: Basement meta-
sedimentary and igneous rocks. New Zealand journal of
geology and geophysics 11: 1009-1040.
Smillie, R. W. 1989: Granite Harbour Intrusives from the Taylor
Valley and Ferrar Glacier region, southern Victoria Land,
Antarctica. Unpublished M.Sc. thesis, lodged in the Library,
University of Otago, New Zealand.
Smillie, R. W. 1992: Suite subdivision and petrological evolution of
granitoids from the Taylor Valley and Ferrar Glacier region,
south Victoria land. Antarctic science 4: 71-87.
Smith, W. C. 1924: The plutonic and hypabyssal rocks of southern
Victoria Land, Antarctica. BritishAntarctic ("TerraNova ")
Expeditions 1910-13 natural history report geology 1:
167-227.
Streckeisen, A. 1976. To each plutonic rock its proper name. Earth
science reviews 12: 1-33.
Streckeisen, A.; LeMaitre, R. W. 1979: A chemical approximation
to the modal QAPF classification of the igneous rocks.
Neues Jahrbuch fur Mineralogie Abhandlungen 136:
169-206.
Stump, E.; Holloway, J. R.; Borg, S. G.; Lapham, K. E. 1983:
Bowers graben and associated tectonic features across
northern Victoria Land, Antarctica. Nature 304: 334-335.
Talarico, F.; Memmi, I.; Lombardo, B.; Ricci, C. A. 1987:
Thermobarometry of granulite-rocks from the Deep Freeze
Range, North Victoria Land, Antarctica. GeologicalSociety
of Italy memoirs 33: 131-141.
Tulloch, A. J.; Rabone, S. D. C. 1987: Geochemistry of
molybdenum-bearing granodiorite porphyries in west
Nelson with special reference to Eliot Creek, Karamea Bend
and Taipo Spur. In: Proceedings of the 21st annual
conference, New Zealand Branch, Australasian Institute of
Mining and Metallurgy.
Vetter, U.; Tessensohn, F. 1987: S- and I-type granitoids of North
Victoria Land and their inferred geotectonic setting.
GeologischeRundschau 76:233-243.
Weaver, S. D.; Bradshaw, J. D.; Laird, M. G. 1984:Geochemistry of
Cambrian volcanics of the Bowers Supergroup and
implications for early Paleozoic tectonic evolution of northern
Victoria Land, Antarctica. Earthandplanetaryscience letters
68: 128-140.
White, A. J. R.; Chappell, B. W. 1983: Granitoid types and their
distribution in the Lachlan fold belt, south east Australia.In:
Roddick, J. A. ed. Circum Pacific plutonic terranes.
Geological Society of America memoir 159:21-34.
Whitten, E. H. T.; Bornhorst, T. J.; Li, G.; Hicks, D. L.; Beckwith,
J. P. 1987: Suites, subdivision of batholiths and igneous-
rock classification: geological and mathematical concept-
ualization. Americanjournal of science 287: 332-352.
Williamson, B.J.;Downes, H.;Thirlwall,M.F. 1992:The relationship
between crustal magmatic underplating and granite genesis:
an example from the Velay granite complex, Massif Central,
France. Transactions of the Royal Society of Edinburgh
earth sciences 83: 235-245.
Wyborn, L. A. I.; Wyborn, D.; Warren, R. G.; Drummond, B. J.
1992: Proterozoic granite types in Australia: implications
for lower crust composition, structure and evolution.
Transactions of theRoyalSocietyofEdinburghearth sciences
83: 201-209.
Downloadedby[GNSScience]at17:3306December2015](https://image.slidesharecdn.com/40f4fe06-ea64-41b9-9fb7-8f7cfe8fb440-151207013515-lva1-app6892/75/Dry-Valleys-Granites-19-2048.jpg)
Uploaded byRobert Smillie
Dry Valleys Granites
This document discusses the geochemistry and evolution of granitoid plutons in the Dry Valleys area of southern Victoria Land, Antarctica. It finds that the plutons can be divided into three suites based on their chemistry and field relationships: 1) the older DV1a and DV1b suites which were emplaced before major dike swarms and were formed during subduction along the early Paleozoic Antarctic Craton margin, and 2) the younger DV2 suite which postdates the dike swarms and was formed during later extension between 480-455 million years ago. The relationships between the hornblende-biotite and biotite granitoids of the D
More Related Content
Dry Valleys Granites
- 1. Full Terms &Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=tnzg20 Download by: [GNS Science] Date: 06 December 2015, At: 17:33 New Zealand Journal of Geology and Geophysics ISSN: 0028-8306 (Print) 1175-8791 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzg20 Granitoids of the Dry Valleys area, southern Victoria Land: Geochemistry and evolution along the early Paleozoic Antarctic Craton margin Andrew H. Allibone , Simon C. Cox & Robert. W. Smillie To cite this article: Andrew H. Allibone , Simon C. Cox & Robert. W. Smillie (1993) Granitoids of the Dry Valleys area, southern Victoria Land: Geochemistry and evolution along the early Paleozoic Antarctic Craton margin, New Zealand Journal of Geology and Geophysics, 36:3, 299-316, DOI: 10.1080/00288306.1993.9514577 To link to this article: http://dx.doi.org/10.1080/00288306.1993.9514577 Published online: 23 Mar 2010. Submit your article to this journal Article views: 80 View related articles Citing articles: 26 View citing articles
- 2. New Zealand Journalof Geologyand Geophysics,1993, Vol.36: 299-316 0028-8306/93/3603-0299 $2.50/0 © The Royal Society of New Zealand 1993 299 Granitoids ofthe Dry Valleys area, southern Victoria Land: geochemistry and evolution along the early Paleozoic Antarctic Craton margin ANDREW H. ALLIBONE Department of Geology James Cook University of North Queensland Townsville, Q4811, Australia* SIMON C. COX ROBERT. W. SMILLIE Department of Geology University of Otago P.O. Box 56 Dunedin, New Zealand *Present address: Etheridge and Henley Geoscience Consultants, P.O. Box 3778,Manuka, A.C.T 2603, Australia. Abstract Field relationships and geochemistry indicate granitoid plutons of the Dry Valleys area comprise at least three petrogenetically distinct suites.The older Dry Valleys 1a (DV1a) suite, comprising the Bonney, Catspaw, Denton, Cavendish, and Wheeler Plutons and hornblende-biotite orthogneisses, and Dry Valleys 1b (DV1b) suite, comprising the Hedley, Valhalla, St Johns, Dun, Calkin, and Suess Plutons,biotite granitoid dikes and biotite orthogneisses, were emplaced before prominent swarms of Vanda mafic and felsic dikes. Both the DV1a and DV1b suites are time transgressive, with older intrusions in each suite being emplaced during the later stages of deformation of the Koettlitz Group. Younger granitoids that postdate the majority of the Vanda dikes include: the Dry Valleys 2 (DV2) suite, comprising the Pearse and Nibelungen Plutons plus several smaller, unnamed plugs; and the Harker, Swinford, Orestes, and Brownworth Plutons with identical field relationships and enclaves but distinct chemistries. Chemical characteristics and limited Rb-Sr isotopic dating indicate plutonism before c. 500 Ma was dominated by the Cordilleran I-type DV1a suite, inferred to have developed during melting above a west-dipping subduction zone along the Antarctic Craton margin. The chemical characteristics of the DV1b suite indicate large-scale melting of a quartzo- feldspathic protolith lacking residual plagioclase, but con- taining refractory garnet. Potential DV1b suite source rocks include metamorphosed immature sediments, possibly underplated along the subduction zone associated with DV1a magmatism, or older granitoid orthogneisses. Major DV1b plutonism at 490 Ma marks the end of subduction-related plutonism in southern Victoria Land. Younger DV2 alkali- calcic, Caledonian I-type plutonism is inferred to have formed in response to uplift and extension between 480 and 455 Ma. G92027 Received 2 June 1992; accepted 29 April 1993 Lack of DV2 suite correlatives and Vanda mafic and felsic dikes in northern Victoria Land suggests significantly different tectonomagmatic histories along the early Paleozoic Antarctic Craton margin. Keywords geochemistry; granitoids; plutons; suites; petrogenesis; southern Victoria Land; Antarctica; Dry Valleys INTRODUCTION Recently, Smillie (1992) proposed a two-fold suite sub- division of granitoids in the Dry Valleys area of southern Victoria Land, based on an integrated study of granitoid field relationships and geochemistry in the Taylor Valley and Ferrar Glacier area. The older Dry Valleys 1 (DV1) suite comprises metaluminous, Cordilleran style, calc-alkaline I-type grani- toids varying in composition from monzodiorite through quartz-monzodiorite and granodiorite to granite. Granitoids included in the DV1 suite by Smillie (1992) form two distinct lithologic varieties: hornblende-biotite, commonly K-feldspar megacrystic plutons; and equigranular biotite granitoids, lacking hornblende. The relationship of these two varieties of granitoid within the DV1 suite is unclear, and geochemistry discussed by Smillie (1989) indicates that they cannot be related by simple fractional crystallisation. The younger Dry Valleys 2 (DV2) suite comprises metaluminous, Caledonian style, alkali-calcic, I-type granitoids, the compositions of which range from monzonite through quartz-monzonite to granite. DV1 granitoids are generally enriched in TiO2,MgO, CaO, V, Sc, and Cr and depleted in K2O, Rb, Pb, and Zr relative to DV2 granitoids. Smillie (1992) inferred generation of the DV1 suite during subduction along the Paleozoic Antarctic Craton margin, and probable emplacement of the DV2 suite during a later phase of extension, postdating subduction. Analysis of older orthogneisses intercalated with Koettlitz Group metasediments (Cox & Allibone 1991) indicates that the two distinct orthogneiss lithologic types (hornblende- biotite and biotite only) are, with the exception of the Dun Pluton, chemically identical to younger, relatively unde- formed hornblende-biotite and biotite granitoids that make up the DV1 suite. Consequently, emplacement of the DV1 suite was inferred to span at least the later stages of Koettlitz Group deformation (Cox 1993). Interrelated plutonism and deform- ation during emplacement of the regional-scale Bonney Pluton is discussed by Cox (1993). Garnet-bearing ortho- gneisses intercalated with Koettlitz Group rocks south of the study area (Skinner 1983; Findlay 1985) are not discussed here, and their relationship to the granitoids of the Dry Valleys area is currently unknown. In Allibone et al. (1993a, this issue) we presented a map and general description of the major plutons in the Dry Valleys area, and a summary of the regional geology (see Fig. 1).An intrusive history was derived from plutonic field relationships, Downloadedby[GNSScience]at17:3306December2015
- 3. 300 New ZealandJournal of Geology and Geophysics, 1993, Vol. 36 77.00 McMurdo Sound -I • DV2 and DV2 ? plutons SP = Swinford Pluton Hybrid plutons BP - Brownworth Pluton Vanda mafic and felsic dikes Packard Pluton, gabbro DV1b undeformed plutons DVIa undeformed plutons CP = Cavendish Pluton Gabbroic and dioritic orthogneiss DV1b orthogneiss DV1a orthogneiss Koettlitz Group Salmon Marble Formation Hobbs Formation Scale 10 km Fig. 1 Inferred basement geology if overlying ice, sediments, moraine, and Ferrar Dolerite were removed to expose the Kukri Erosion Surface. The DVIa and DVlb plutons (Bonney, Wheeler, Denton, St Johns, Valhalla, and Hedley Plutons) have a consistent northwest orientation and are cut by northeast-striking younger dikes and the ovoid Pearse, Nibelungen, Brownworth, Orestes, Swinford, and Harker Plutons. Downloadedby[GNSScience]at17:3306December2015
- 4. Allibone et al.—Geochemistryof granitoids, Antarctica 301 and this was correlated with new and earlier radiometric data. Pluton mapping indicated that hornblende-biotite granitoids (included in the DV1 suite of Smillie 1992) are generally ellipsoidal, deep-level, concordant plutons, with northwest- trending axes parallel to the belts of Koettlitz Group metasediment. In contrast, equigranular biotite granitoids (also included in the DV1 suite by Smillie 1992) are similarly elongate in a northwest direction, but are generally younger discordant plutons, which intruded by stoping at c. 490 Ma ago. Swarms of northeast-trending Vanda mafic and felsic porphyry dikes crosscut these hornblende-biotite and biotite granitoid plutons. Most of the Vanda mafic and felsic dikes were subsequently intruded by discordant ellipsoidal-shaped plutons between 480 and 455 Ma. The occurrence of rare Vanda mafic and felsic porphyry dikes cutting the younger discordant plutons, and magmatic microgranitoid enclaves resembling Vanda dike rocks within these plutons, indicates emplacement of the Vanda dike swarms continued during and after the emplacement of the discordant kilometre-scale granitoid plutons. This part of our study deals with the geochemistry of plutons and the evolution of granitoids in southern Victoria Land. Plutons mapped and described in Allibone et al. (1993a) are shown in Fig. 1. New analyses of these plutons are presented (Table 1), and their suite affinities examined. Unravelling the relationship of hornblende-biotite and biotite granitoids within the DV1 suite, and their relationship to the Dun Pluton, is of particular interest. We test the applicability of Smillie's (1992) DV1/DV2 suite subdivision to the new plutons mapped and to a wider area of southern Victoria Land. We outline problems associated with previous granitoid subdivision schemes applied in southern Victoria Land, in an attempt to relate our mapping to previous studies. Similarities between the granitoid geology of the Dry Valleys area and other parts of the Transantarctic Mountains as far north as Terra Nova Bay have been inferred since the early studies of Priestley (1914), Mawson (1916), and Smith (1924). Subsequent mapping of Larsen Granodiorite (named from Mt Larsen in northern Victoria Land) and Irizar Granite (named from Cape Irizar immediately south of Terra Nova Bay) in northern and southern Victoria Land, by Gunn & Warren (1962), reinforced the earlier correlations of granitoid rocks from throughout the Ross Sea sector of the Trans- antarctic Mountains. The recent publication of major and trace element analyses of granitoids in each of the terranes of northern Victoria Land (e.g., Borg et al. 1987; Armienti et al. 1990),combined with the data included in this study, allows a revision of these earlier correlations between granitoids of northern and southern Victoria Land. Comparison of the isotopic character of granitoids in the central Transantarctic Mountains (Borg et al. 1990) and the Dry Valleys allows a clarification of the correlation of granitoids and "basement terranes" in these two areas. Reinterpreted dates (Allibone et al. 1993a) are used to provide age constraints on the geochemical, tectonic, and petrogenetic evolution of the southern Victoria Land margin of the Antarctic Craton during the early Paleozoic. GRANITOID GEOCHEMISTRY Analytical methods Chemical analysis of granitoid samples was undertaken to clarify relationships and the petrogenetic evolution of the various plutons and granitoid dike swarms described in Allibone et al. (1993a). X-ray fluorescence analyses were carried out using Sc, Mo, and Au tubes in the University of Otago Geology Department's Philips PW1410/20 AHP Spectrometer. Samples were washed, then crushed in a tungsten carbide swing mill. Major elements were determined on fused disks using the method of Norrish & Hutton (1969). Trace elements were determined on 5 g, 32 mm pressed powder pellets using Mowiol (PVA) binder, and based on the Norrish & Chappell (1977) procedures. Selected duplicate samples were analysed by the analytical facility atJames Cook University of North Queensland to confirm the accuracy of results. Analyses are listed in Table 1. In addition to our new analyses, data from Palmer (1987, 1990), Allibone (1988), Smillie (1989), Cox (1989), Ellery (1989), and Cox & Allibone (1991) have been used in this paper. Data collected for orthogneisses described in Cox & Allibone (1991) are integrated with data from this and the above studies, requiring a reinterpretation of orthogneiss petrogenesis. Normative QAP compositions and DV1/DV2 suite affinities Plotting normative compositions of the various plutons and dikes described in Allibone et al. (1993a) on the Streckeisen (1976) QAP diagram defines two clear trends (Fig. 2). These trends are synonymous with the calc-alkaline (DV1) and alkali-calcic (DV2) suite trends described by Smillie (1992). The Bonney, Cavendish, Denton, Wheeler, Catspaw, Hedley, Valhalla, St Johns, Suess, Dun, Calkin, Orestes, and Brownworth Plutons, various biotite granodiorite and granite dikes, and hornblende-biotite and biotite orthogneisses plot along the DV1 trend of Smillie (1992),ranging in composition from monzodiorite to granite. The Pearse, Rhone, and Nibelungen Plutons, unnamed quartz-monzonite dikes and plugs, and all the Vanda felsic porphyry plugs and dikes plot along the DV2 trend of Smillie (1992),ranging in composition from monzonite to granite. The Pearse and Nibelungen Plutons are the first kilometre-scale plutons identified as part of the DV2 suite. Several additional features are apparent. Biotite granitoids (Hedley, Valhalla, Suess, and St Johns Plutons, and unnamed biotite granite dikes and plugs—solid symbols on Fig. 2) plotting in the DV1 field of Smillie (1992) form a tightly constrained trend within the broader DV1 suite trend defined by the hornblende-biotite granitoids (Bonney, Cavendish, Denton, Wheeler, and Catspaw Plutons—open symbols on Fig. 2). This apparent similarity in QAP composition is not sufficient to confirm a petrogenetic relationship between the two petrographically distinct granitoid types, within the DV1 suite of Smillie (1992). The relatively young, discordant Swinford, Orestes, Brownworth, Pearse, and Nibelungen Plutons, whose emplacement postdates the majority of the Vanda mafic and felsic porphyry dikes (Fig. 3), plot in both the DV1 and DV2 suite trends on Fig. 2, defined by Smillie (1992). This implies the younger, discordant, granitoid plutons do not form a geochemically coherent suite, despite their similar field relationships, enclaves, and inferred pluton shapes. Instead, a more complex petrogenesis is implied, with only the Pearse and Nibelungen Plutons having field relationships and alkali- calcic geochemistry analogous to the DV2 suite of Smillie (1992). Analyses of the Harker Pluton indicate a highly Downloadedby[GNSScience]at17:3306December2015
- 5. Table 1 XRFanalyses of granitoids from the Dry Valleys region of southern Victoria Land. Sample numbers with prefix "P"refer to samples lodged in the petrology collection, Institute of Geological & Nuclear Sciences, Lower Hutt, whereas those with prefix "O"refer to specimens in the University of Otago Geology Department's rock and mineral collection. Major elements are in weight %, trace elements in ppm. n.d. = not determined, b.d. = below detection. Sample OU60757 OU60745 OU60746 OU60749 OU60750 OU60762 OU60763 P49935 OU60760 P49911 OU60752 OU60761 OU61128 OU61136 OU61135 OU61134 OU6H33 OU61118 VU30818 VU30823 VU30821 OU61037 P49933 P50185 P50190 P50161 P50184 OU60557 P49932 P49934 P49935 OU56854 OU56855 P49945 P49962 P49948 P49963 P49964 P49928 P49950 P49949 OU60478 OU60506 OU60509 OU60464 P50178 P50177 P5O18O P50163 P50169 P50170 P50162 P50171 P50167 Long. E 162-15' 161-40' 161-52' 161-40' 161-42' 162-16' 162-16' 161-56' 162-14' 161-38' 161-44' 162-14' 162-26' 162-31' 162-29' 162-33' 162-40' 162-13' 161-39' 161-40' 161-45' 161°41' 162-01' 161-49' 161-48' 161-36' 161-40' 162-08' 162-03' 162-02' 161-56' 161-56' 162-16' 161-52' 161-37' 161-56' 161-46' 161-43' 161-22' 162-00' 162-00' 162-11' 162°15' i62°ir 162-16' 161°31' 161-38' 161-15' 161-37' 161-40' 161-39' 161-37' 161-40' 161-39' Lat. S 77-29.7' 77-31.3' 77-31.1' 77-31.3 77-31.3 77-31.5' 77-31.0' 77-46.9' 77-29.9 77-42.9' 77-31.3' 77-29.9 77-26.4' 77-29.2' 77°28.6' 77-29.0' 77-29.5' 77-27.3' 77-06.8' 77-09.3' 77-07.7' 77°43.4' 77°49.3' 77-42.3' 77-48.0' 77-42.0' 77-40.4' 77-48.0' 77-48.4' 77-49.5' 77°46.9' 77-03.9' 77-48.9' 77-33.4' 77-42.0' 77-33.8' 77-30.9' 77-31.0' 77-49.6' 77-33.6' 77-33.6' 77-42.6' 77-44.0' 77-44.6' 77-42.6' 77-46.0' 77-45.1' 77-45.1' 77-41.9' 77-42.2' 77-42.4' 77-42.0' 77-02.8' 77-41.8' Pluton Bonney Bonney Bonney Bonney Bonney Bonney Bonney Bonney Bonney Bonney Bonney Bonney Denton Denton Denton Denton Denton Denton Wheeler Wheeler Wheeler Catspaw Catspaw Catspaw Catspaw Catspaw Catspaw Hedley Hedley Hedley Hedley Hedley Hedley Valhalla Valhalla Valhalla UBGSP UBGSP UBGSP JBGSP UBGSP UBGSP UBGSP Felsic Porphyry Felsic Porphyry Felsic Porphyry Felsic Porphyry Felsic Porphyry UQM, MSP UQM, MSP UQM, MSP UQM, MSP UQM, MSP UQM, MSP SiO2 57.36 62.65 62.88 63.31 63.89 64.38 64.73 65.70 67.34 68.35 70.05 72.56 60.53 64.31 64.73 64.93 70.96 71.38 57.01 63.41 66.13 71.02 71.44 72.31 72.33 72.56 72.78 68.17 70.13 70.40 70.50 71.48 73.58 71.45 71.48 73.58 71.89 72.05 73.71 74.82 75.37 75.55 75.97 64.02 66.47 70.58 71.11 71.74 59.50 60.57 60.73 60.74 63.01 67.83 TiO2 1.05 0.78 0.86 0.83 0.78 0.70 0.66 0.66 0.54 0.55 0.38 0.24 0.89 0.66 0.58 0.63 0.42 0.39 0.47 0.60 0.57 0.31 0.31 0 0 0.28 0.23 0.22 0.30 0.28 0.32 0.29 0.27 0.14 0.24 0.27 0.14 0.18 0.18 0.19 0.08 0.05 0.07 0.07 0.55 0.41 0.29 0.28 0.23 0.79 0.77 0.63 0.66 0.57 0.38 A12O3 19.81 15.93 16.47 16.44 16.14 16.55 16.96 15.83 15.95 14.95 14.76 14.23 17.06 15.13 16.79 16.62 15.40 14.04 19.83 16.76 15.92 14.42 14.29 14.01 13.78 13.96 13.66 16.49 15.59 15.38 15.46 15.41 14.58 14.67 15.41 14.58 15.40 15.45 14.54 13.66 13.46 13.34 13.13 16.17 15.68 14.08 14.14 14.13 17.96 17.58 17.84 17.93 16.93 15.71 Fe2O3T 6.80 5.45 6.27 5.59 5.13 4.99 4.41 4.42 3.76 3.48 2.98 1.68 6.39 5.83 4.45 4.56 2.79 2.63 4.28 4.92 4.51 2.43 2.40 2.07 2.52 2.12 2.37 2.39 1.95 2.18 2.01 2.24 1.32 2.03 2.24 1.32 1.44 1.39 1.38 1.04 0.79 1.15 0.41 5.03 4.02 2.40 2.47 2.31 5.71 5.69 5.23 5.69 4.85 3.30 Fe2O3 0.90 1.43 1.54 0.89 0.91 1.65 1.23 n.d. 0.74 n.d. 0.59 0.71 n.d. n.d. n.d. n.d. n.d. n.d. 0.65 0.89 0.74 n.d. n.d. n.d. n.d. n.d. n.d. 0.62 n.d. n.d. n.d. 0.82 0.18 n.d. 0.82 0.18 n.d. n.d. n.d. n.d. n.d. 0.21 0.10 0.88 1.18 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. FeO 5.31 3.62 4.26 4.23 3.80 3.01 2.86 n.d. 2.72 n.d. 2.15 0.87 n.d. n.d. n.d. n.d. n.d. n.d. 3.27 3.63 3.39 n.d. n.d. n.d. n.d. n.d. n.d. 1.59 n.d. n.d. n.d. 1.28 1.03 n.d. 1.28 1.03 n.d. n.d. n.d. n.d. n.d. 0.85 0.28 3.73 2.56 n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. MnO 0 0 0.08 0.09 0.08 0.08 0.06 0.06 00 0.00 0.06 0.05 0.00 0.10 0.10 0.05 ONOe 0.03 0.04 0.10 0.08 0.08 0.04 0.04 0.04 0.05 0.04 0.04 0.03 0.03 0.03 0.03 0.03 0.02 0.03 0.03 0.02 O^ON ONON 0.03 0.03 0.02 0.04 0.00 0.09 0.07 0.04 0.04 0.04 0.08 0.08 0.09 0.09 oooo 0.06 MgO 2.16 1.84 1.98 1.96 1.65 2.17 1.47 1.56 1.11 1.37 0.88 0.42 2.25 1.94 1.55 1.30 0.79 0.78 2.76 1.79 1.33 0.48 0.49 0.28 0.51 0.32 0.33 0.56 0.46 0.50 0.47 0.48 0.26 0.40 0.48 0.26 0.26 0.27 0.27 0.08 0.04 0.17 0.11 1.24 0.69 0.39 0.34 0.37 1.27 1.21 0.99 0.98 0.90 0.61 CaO 5.65 4.31 4.59 4.32 4.07 4.19 4.46 3.76 3.40 3.26 2.77 1.90 4.87 3.78 3.81 3.84 2.61 2.51 8.14 4.11 3.66 1.83 1.84 1.45 1.71 1.69 1.44 2.95 2.42 2.44 2.34 2.35 1.84 2.41 2.35 1.84 2.04 2.09 1.60 1.21 1.05 1.20 1.46 3.53 2.46 1.71 1.64 1.54 3.83 3.68 3.29 3.35 2.99 2.22 Na2O 4.05 4.29 3.16 3.05 3.17 3.53 3.47 3.89 2.74 3.00 2.51 2.28 3.85 2.99 3.11 3.24 3.88 2.85 4.77 3.59 3.60 3.26 3.52 4.22 3.89 3.38 3.31 3.81 3.62 3.85 3.72 3.73 3.60 3.22 3.73 3.60 4.10 3.94 4.01 3.60 3.59 3.41 2.26 3.59 3.18 2.99 2.89 3.59 4.31 4.25 4.19 4.39 4.26 4.04 K2O 2.61 3.68 3.11 3.68 3.98 2.40 3.14 3.98 4.28 4.27 5.06 5.86 3.03 3.85 4.12 3.78 3.04 4.49 1.76 3.81 3.59 4.90 4.65 4.79 4.48 4.45 4.44 3.27 4.08 3.83 4.07 4.17 4.53 4.43 4.17 4.53 3.78 4.01 4.44 4.42 4.69 4.54 5.83 5.06 5.45 5.59 5.76 5.64 5.03 5.08 5.94 5.50 5.43 5.39 P2O5 0.24 0.27 0.21 0.19 0.19 0.23 0.22 0.15 0.14 0.13 0.09 0.06 0.22 0.16 0.16 0.16 0.10 0.10 0.24 0.18 0.15 0.06 0.07 0.04 0.07 0.04 0.04 0.06 0.06 0.06 0.07 0.06 0.04 0.04 0.06 0.04 0.03 ONON 0.02 0.01 0.00 0.02 0.01 0.22 0.13 0.06 0.06 0.06 0.22 0.20 0.17 0.17 0.15 0.09 LOI 1.03 1.17 0.91 0.99 1.11 1.39 0.74 0.62 0.74 1.14 0.76 0.52 0.37 0.85 0.53 0.51 0.32 0.23 0.96 1.00 0.88 0.52 0.63 0.54 0.50 0.65 0.60 0.68 0.67 1.21 0.80 0.54 0.57 0.59 0.54 0.57 0.51 ^5O 0.48 0.35 0.35 0.47 0.54 1.04 1.25 0.87 0.67 1.01 0.95 0.41 0.39 0.43 0.41 0.63 Total 100.25 100.04 100.06 99.97 99.77 100.25 99.98 N00©O 99.74 100.60 100.05 99.66 99.57 99.62 99.89 99.63 100.30 99.46 99.96 99.85 100.04 99.27 99.66 99.97 100.10 99.44 99.24 98.53 99.28 100.20 99.76 100.62 100.37 98.88 100.62 100.37 99.66 99.94 100.70 99.31 99.40 99.87 99.76 100.12 99.53 98.99 99.41 100.70 99.63 99.53 99.49 99.93 99.58 100.30 Ga 30 24 26 21 22 21 19 N0 16 7 16 12 24 21 24 22 23 20 26 23 21 17 19 17 10 15 19 22 12 im 9 16 16 8 15 8 18 ^5 15 15 8 19 11 19 19 15 15 18 18 18 16 16 20 16 Rb 124 140 120 156 184 105 100 139 119 138 184 118 154 135 163 123 92 136 101 150 147 180 184 157 185 158 141 95 114 151 111 133 133 121 124 144 134 131 117 173 121 214 147 268 378 257 260 240 132 152 145 131 157 177 Sr 587 479 443 483 422 434 499 485 563 417 469 512 496 437 442 481 542 382 808 420 390 291 2:2 174 210 198 185 674 578 557 653 409 408 445 363 347 631 576 422 344 445 162 546 536 367 261 254 235 896 794 816 716 584 476 Y 19 37 43 26 20 12 17 23 17 24 20 5 38 54 33 27 7 20 17 45 30 22 21 27 25 23 27 17 8 9 9 9 5 9 NI 10 12 7 8 12 9 13 b.d. 40 38 30 27 30 23 17 24 25 33 23 Zr 295 207 233 203 219 165 211 182 199 161 134 104 234 214 211 228 136 152 89 iwi 183 180 183 159 181 162 190 195 172 172 169 182 117 145 122 134 122 124 115 93 145 70 19 272 265 203 194 224 455 472 430 526 404 272 Pb 15 19 19 20 23 14 17 00 21 20 26 22 19 18 23 20 22 22 17 27 23 24 19 27 27 23 25 24 20 im 20 21 24 20 24 23 25 19 25 28 20 38 24 22 24 21 27 30 23 22 30 27 27 28 Th 17 24 17 23 22 13 9 iO 10 9 18 5 20 8 40 24 8 iV 5 iw 20 16 17 14 18 15 16 10 10 ni 7 10 7 6 6 7 b.d. b.d. b.d. b.d. 6 12 b.d. 20 22 22 27 28 7 8 7 7 15 14 NC 8 6 6 6 6 10 6 6 6 5 5 4 9 10 7 6 7 6 b.d. b.d. b.d. 5 4 4 5 5 2 3 3 4 3 2 2 4 4 3 5 5 2 3 5 3 2 5 5 4 5 6 5 7 5 5 6 4 Cu 5 2 1 2 2 7 b.d. 2 4 5 b.d. 18 7 b.d. b.d. 1 1 b.d. b.d. b.d. b.d. 2 2 2 3 3 2 b.d. 3 4 2 b.d. b.d. 2 1 2 4 3 3 6 2 b.d. 1 7 3 2 2 2 5 65 4 5 3 4 i n 102 72 86 78 75 83 70 67 61 60 44 27 88 87 78 66 60 45 67 77 73 56 46 53 59 84 58 49 43 48 43 39 30 52 42 38 35 ^5 33 23 22 28 6 95 60 48 47 50 84 96 79 84 84 63 NP 25 16 18 14 15 18 14 iO 12 12 13 6 24 23 23 22 19 iV 9 iw 17 15 14 15 14 14 16 17 9 9 8 8 8 9 9 10 ^O 9 8 13 12 11 b.d. 19 29 16 15 17 18 15 17 17 21 15 V 75 63 73 65 63 74 Mi 52 32 40 24 b.d. 80 64 49 44 27 27 86 57 40 15 18 11 17 13 11 b.d. 11 im 9 16 7 10 9 9 4 b.d. 5 b.d. 6 6 8 26 16 15 14 10 18 18 6 12 14 11 CN 16 12 14 •O 10 21 11 iO b.d. 10 b.d. b.d. 26 27 11 iN 9 8 27 iw 13 7 7 4 5 b.d. 4 b.d. 6 6 6 4 b.d. 5 b.d. 4 4 b.d. 4 4 b.d. 5 6 10 7 6 6 4 8 7 6 6 5 5 Ba 557 800 599 947 729 300 847 861 1646 1217 1380 1910 850 1041 935 1021 1152 656 335 807 786 835 794 580 638 513 625 1415 1247 1150 1183 209 903 1044 829 908 1098 1217 832 853 420 269 2135 804 630 658 596 556 2034 2107 2496 1684 1625 999 La 82 52 53 49 62 61 52 49 42 37 32 18 55 22 100 76 33 44 14 41 54 41 : 2 28 47 24 45 50 46 42 35 36 22 43 27 33 10 12 12 6 b.d. 10 6 63 63 65 69 68 61 51 59 74 83 77 Ce 148 102 11 103 126 107 103 95 92 86 81 60 115 57 191 136 60 87 25 76 93 97 93 76 102 67 101 97 104 96 93 61 34 94 78 81 56 62 57 45 34 19 b.d. 120 122 132 141 139 125 116 147 152 167 154 Pr 10 12 14 12 14 14 13 iO 8 10 9 7 13 8 19 iN 5 5 n.d. n.d. n.d. 7 8 9 10 8 10 n.d. 8 6 7 n.d. n.d. 10 9 7 7 8 b.d. b.d. b.d. n.d. n.d. n.d. n.d. 13 13 17 13 6 10 18 17 15 NH 44 35 48 34 45 30 32 25 26 24 21 11 47 34 73 49 20 28 n.d. n.d. n.d. 28 22 23 31 15 30 27 19 im 15 n.d. n.d. 23 14 19 b.d. 7 b.d. b.d. b.d. b.d. b.d. 44 48 46 44 48 42 b.d. 44 54 61 15 ^ «t S o oo 5" 1Q 1 f 5 |u> Downloadedby[GNSScience]at17:3306December2015
- 6. Allibone et al.—Geochemistryof granitoids, Antarctica Fig. 2 Normative QAP composi- tions of analyses of the various plutons plotted after Streckeisen (1976). Compositions of the DV1 and DV2 suites from Smillie (1992) areplotted for comparison. Granitoids mapped during this study show an identical two-fold subdivision into theDV1 andDV2 suites of Smillie (1992). Biotite granitoids within the DV1 suite (solid symbols) form a narrow, well-defined trend within the broader DV1 suite field of Smillie (1992). Data are from this study, Palmer (1987, 1990), and Ellery (1989). 303 v i O N © " ^ •**•**—NO"^•**•** — N O m I « » DC VI -H t—CT>l/l t^ © (N © N o o w - i w - i u - i r - oot--© r r - r - r N p r - v i m m m r j i n © © © q o © o — © o © o © © © © © d d © d o © ' © 8SSS58SSSS3S © © ' © d o d o © © © © © q q q q c c c c d d d d d d o d © © © © |^j ^ j ^ j r ^ pQ OO n *—> — oo §§iSS Q60:AP40 quartz-monzonitel M quarU-monzodiorite Tnonrartom6 A65:P35 X Marker Pluton v Swinford Pluton 4- Pearse Pluton O Brownworth Pluton • Biotite granite dikes M Quartz-monzonite sills + Felsic porphyry plugs A35:P65 A10:P90 • Orestes Pluton A Valhalla Pluton T Hedley Pluton • Suess Pluton 4 St. Johns Pluton o Catspaw Pluton A Denton Pluton V Bonney Pluton .,/2>Bonney Pluton (Smillie1992) 1 D V 1 s u i t e (Smilli e 1992) O D V 2 suite (Smillie1992) evolved composition, which plots at the intersection ofthe DV1 andDV2 trends (Fig. 2).Further analysis is required to define thesuite affinity ofthe Harker Pluton. Relationship ofhornblende-biotite and biotite granitoids within theDV1 suite ofSmillie (1992), and the"Dun Type" orthogneiss ofCox &Allibone (1991) In many ofthe discriminant and variation diagrams presented below, hornblende-biotite granitoids of the DV1 suite (hornblende-biotite orthogneisses, Bonney, Denton, Cavendish, Wheeler, andCatspaw Plutons) display distinctly different evolutionary trends from biotite granitoids ofthe DV1 suite (Hedley, Valhalla, Suess, and St Johns Plutons, biotite orthogneisses including theDunandCalkin Plutons, and biotite granite dikes). This implies that theDV1 suite,as defined by Smillie (1992), comprises two,petrogenetically distinct suites. Thedistinct geochemistry of thehornblende- biotite andbiotite granitoids previously included in the DV1 suite bySmillie (1992) isconsistent with the different styleof emplacement of the major hornblende-biotite granitoid plutons (Bonney, Denton, Cavendish, Wheeler) and biotite granitoid plutons (Hedley, Valhalla, StJohns, Suess) outlined in Allibone et al. (1993a). Accordingly, in the following discussion, the hornblende-biotite granitoids are referred to as DVla suite granitoids, andbiotite granitoids as DVlb suite granitoids. TheDVla and DVlb suites are petrogenetically distinct and unlikely to be derived from the same source material. They are not subdivisions of a larger overallDV1 suite. DV1 is retained inthename of each suite to emphasise the partly coeval, time transgressive nature of the DVla and DVlb suites, inferred from field relationships outlined in Allibone etal. (1993a) and illustrated inFig.3. Harker variation diagrams (Fig. 4) indicate DVlb biotite granitoids are enriched in A12O3, Na2O, and Sr relative to DVla hornblende-biotite granitoids. Both types define distinctly different trends on the variation diagrams. The slopes of the A12O3 versus SiO2, Na2O versus SiO2 and Sr versus SiO2 trends for the DVlb biotite granitoids are Downloadedby[GNSScience]at17:3306December2015
- 7. 304 New ZealandJournal of Geology and Geophysics, 1993,Vol. 36 migmatite development —isoclinal folding upright folding about NNW trending axes KOETTLITZ GROUP hornblende-biotite orthogneiss . Bonney | i Denton 1 Wheeler ., Cavendish . .Catspaw, DRY VALLEYS 1a (DV1a) SUITE Dun Calkin biotlte orthogneiss Medley Valha St.Johns DRY VALLEYS 1b (DV1b) SUITE VANDA MAFIC DIKES I Orestes . Brownworth STRONG DRY VALLEYS 2 CHARACTER DRY VALLEYS 2 (DV2) SUITE • qtz monzonite. 'dikes & plugs' Pearse t Nibelungen H oldest 5 8 6 ' ' 4 9 0 AGE Ma NOT TOSCALE 486 I 477 I youngest Fig. 3 The inferred relative timing of emplacement of the various plutons,dike swarms,and granitoid suites mapped. Emplacement ofthe DVla andDVlb suites overlaps withthe later stages of deformation and migmatitedevelopment inthe Koettlitz Group.Emplacement ofthe DV2 suite postdates emplacement of the DVla and DVlb suites, and the majority of the VandaDikes. especially steep relative to the DVla hornblende-biotite granitoids. DVlb granitoids are also highly enriched in Ba relative to DVla granitoids (Fig. 4), but values for biotite orthogneisses show a wider scatter, possibly as a result of incipient to extensive migmatite development. DVlb grani- toids and orthogneisses are extremely depleted in Nb (not plotted here) and Y, and Rb, K2O, MgO, Cr, V, and Th (not plotted here) to a lesser extent, relative to DVla granitoids (Fig. 4; Cox & Allibone 1991). Na2O/K2O ratios (Fig. 5) of DVlb granitoids and orthogneisses are also consistently higher than those of DVla hornblende-biotite granitoids. Chondrite normalised LREE profiles are similar for both the DVla and DVlb granitoids (Fig. 6), but more evolved DVlb granitoids are characterised by lower absolute LREE con- centrations. Analyses of the "Dun Type" orthogneisses (Cox & Allibone 1991) appear to form the less evolved extension of the DVlb biotite granitoid trends, implying the orthogneiss Dun Pluton is also part of the DVlb suite. Structural relationships outlined in Allibone et al. (1991) and Cox & Allibone (1991) imply that emplacement of the Dun Pluton and other biotite orthogneisses occurred before Fj, isoclinal folding of the Koettlitz Group (Fig. 3). The simplest interpretation, consistent with the structural relationships and geochemistry of the Dun Pluton, is that emplacement of the DVlb suite spans a significant part of the structural- metamorphic history of the Koettlitz Group. Radiometric dating (discussed in Allibone et al. 1993a) indicates an age difference anywhere between a few million years and 120Ma separating emplacement of the orthogneiss Dun Pluton and the major DVlb Hedley, Valhalla, St Johns, and Suess Plutons. While the shorter time span is perhaps easier to rationalise with the inferred time scale of tectonomagmatic events, emplacement of small, petrogenetically associated DVlb suite intrusives over 120 Ma may imply a relatively stable tectonomagmatic situation for this length of time. Fig.4 Major andtraceelement Harkerdiagrams illustrating thedifferences andsimilarities inthechemistry ofthevarious granitoidplutons andsuites intheDryValleys area.HarkerdiagramsindicatethattheDVla hornblende-biotite granitoids andtheDVlbbiotitegranitoidsform two,distinct,evolutionary trends."Dun-Type"biotiteorthogneisses (Cox&Allibone 1991)represent themost unevolved oftheDVlbbiotite granitoids, rather than a separate petrogenetic suite. The Orestes Pluton exhibits DVlb geochemistry, despite havingfieldrelationships and enclavestypicalofDV2granitoids,whiletheHarker andSwinford Plutons show close affinities withthe DV2suite.TheBrownworthPluton showsmixed DVla+b andDV2chemical character. Dataarefrom this study, Palmer (1987),Allibone (1988),Ellery (1989), Smillie(1989), and Cox &Allibone(1991). Downloadedby[GNSScience]at17:3306December2015
- 8. 400 300 200 100 1000 Ift 55 60 6570 75 80 55 60 65 70 75 80 55 60 65 70 75 80 55 60 65 70 75 80 •9 O 55 60 65 70 75 80 55 60 65 70 75 80 SiO2 © DVIa granitoid • DV1b granitoid A DVIaorthogneiss * DVIborthogneiss 55 60 65 70 75 2500 55 60 65 70 75 SiO2 x DV2 granitoid • Brownworth * Harker e Swinford 30 25 20 15 10 5 0 Cr ft a ©© © © © a © © «© © © o ft xas © © ©o©» X X L xaA e e© 55 60 65 70 75 80 55 60 65 70 SiO2 I' 55 60 65 70 75 80 55 60 65 70 75 80 SiO2 Downloadedby[GNSScience]at17:3306December2015
- 9. 306 New ZealandJournal of Geology and Geophysics, 1993, Vol. 36 o DV1 a granitoid A DVIaorthogneiss • DV1b granitoid A DVIborthogneiss x DV2 granitoid a Orestes • Brownworth * Harker © Swinford Fig. 5 Na2O versus K2O plot of granitoid analyses. The DVla hornblende-biotite granitoids, DVlb biotite granitoids, and DV2 suite quartz-monzonites and granites each define a distinct evolutionary trend.DVla granitoids arecharacterised by arelatively shallow negative slope,unlike the steeper negative slope defined by themoresodicDVlbbiotitegranitoids.TheK2Ocontent oftheDV2 suite appears independent of the Na2Ocontent. Fields of S-typeand I-type granitoids, after White & Chappell (1983), are plotted for comparison.Dataarefrom this study,Palmer (1987,1990),Allibone (1988),Ellery (1989), Smillie (1989), and Cox &Allibone (1991). Field relationships, petrographic characteristics, and geochemical data all support the subdivision of the DV1 suite as defined by Smillie (1992) into two petrogenetically distinct and unrelated suites. These are the DVla suite consisting of hornblende-biotite granitoids and a DVlb suite consisting of biotite granitoids. Hornblende-biotite and biotite ortho- gneisses described by Cox & Allibone (1991) are inferred to be integral parts of the DVla and DVlb suites, respectively. The structural relationships of individual intrusions within both the DVla and DVlb suites indicates emplacement of both suites spans at least the later stages of deformation and metamorphism of the older Koettlitz Group. Consequently, both the DVla and DVlb suites are inferred to be time transgressive. Each suite represents a continuum of intrusions, rather than a distinct, separate, plutonic event at a specific geologic time (Fig. 3).Thepartly coeval emplacement of these two unrelated granitoid suites indicates coeval melting of distinct protoliths. Comparison of the DV2 suite with the DVla and DVlb suites Analyses of the Pearse Pluton and unnamed quartz-monzonite dikes, plugs, and sills indicate geochemical characteristics analogous to the DV2 suite as defined by Smillie (1992). The Pearse Pluton and the unnamed quartz-monzonite dikes, plugs, and sills both have high K2O, Rb, Pb, and Zr contents relative to the DVla and DVlb suites (Fig.4,5). Analyses also show the DV2 suite intrusions are depleted in MgO, CaO, V, and Cr relative to DVla granitoids, although DV2 suite MgO, V, and Cr contents are similar to DVlb rocks. In addition, less evolved samples of the Pearse Pluton and the unnamed quartz- monzonite dikes are highly enriched in Ba (up to 2500 ppm) and Sr (up to 900 ppm) (Fig. 4). In both the Ba and Sr versus SiO2 variation diagrams (Fig. 4) the DV2 suite granitoids exhibit a steep negative slope, parallel to that defined by the DVlb suite, but at lower SiO2 values, clearly illustrating the different evolutionary trends of each suite. Ba and Sr contents of the DVla suite are lower, with Ba/SiO2 and Sr/SiO2 variation diagrams having a shallower slope than for the DVlb and DV2 suites, again clearly illustrating the different evolutionary trends of each suite. The DV2 suite is enriched in LREE relative to both the DVla and DVlb suites (Fig. 6). Despite overlap between DVla and DV2 suite Na2O, A12O3, and Y contents, and DVlb and DV2MgO,Cr, and V contents, it is apparent that, when the geochemical data are combined with field relationships, three, rather than two, distinct petrogenetic suites, as proposed by Smillie (1992), are present in the Dry Valleys area. Suite affinities of the Swinford, Brownworth, Orestes, and Harker Plutons Field relationships indicate that these four plutons have similar ages and intrusive styles as the granitoids included in the DV2 suite (Allibone et al. 1993a, fig. 3). Felsic porphyry enclaves identical to the Vanda dikes, present in each of these plutons, are also typical of the DV2 suite granitoids described by Smillie (1992). Analyses of these four plutons are plotted in Fig. 4, 5, and 6. They indicate the chemistry of these four plutons deviates from the chemistry characteristic of the DV2 suite as outlined in Smillie (1992). Analyses of the Swinford Pluton indicate a composition generally consistent with DV2 suite characteristics. Only the relatively low K2O and Rb contents of the Swinford Pluton are inconsistent with its DV2 field relationships and felsic porphyry enclave suite.The Harker Pluton is the most evolved granitoid studied. In many variation diagrams (Fig. 4,5,7) the Harker Pluton plots at the intersection of trends defined by two or three of the DVla, DVlb, or DV2 suites. Consequently, the chemistry of the Harker Pluton is generally consistent with it being part of the DV2 suite, with only the low K2O, Rb, and Ba contents of the least evolved samples deviating from the chemical characteristics of the DV2 suite. The Brownworth and Orestes Plutons exhibit few chemical features in common with the DV2 suite as defined by Smillie (1992). This is despite having identical field relation- ships and enclaves. The chemistry of the Orestes Pluton is analogous to the older DVlb suite biotite granodiorites and granites, rather than the DV2 suite. This is consistent with the lack of hornblende in the Orestes Pluton, an important feature of the DVlb suite, and unlike the other younger discordant plutons. The field relationships of the Vanda dikes and the Downloadedby[GNSScience]at17:3306December2015
- 10. Allibone et al.—Geochemistryof granitoids, Antarctica 307 Fig. 6 Chondrite normalised LREE contents of the granitoid samples. DV2 suite granitoids are enriched in LREE relative to DV1a and DVlb suite granitoids. Small peaks in each profile probably reflect the analytical procedure rather than real differences in the relative LREE concentrations. 1000r 800 600 400 200 100 80 60 4 0 20 Dry Valleys 1asuite Dry Valleys 1 b suite Dry Valleys 2 suite + Orestes Pluton —-Brownworth Pluton La Cs Pr Nd La Ce Pr Nd La Ce Pr Nd Orestes Pluton indicate that the Orestes Pluton is probably the oldest of the relatively young discordant plutons, with field relationships and enclaves analogous to the DV2 suite defined by Smillie (1992). This is consistent with the conflicting chemistry, field relationships, and enclaves of the Orestes Pluton, which indicate features in common with both the DVlb and DV2 suite. Whether the Brownworth, Orestes, Harker, and Swinford Plutons are included in the DV2 suite depends on how the DV2 suite is defined. If field relationships and enclave types are emphasised in the suite definition, then all four plutons would be included. Alternatively, if geochemistry is emphasised, then the Orestes Pluton at least would be included in the DVlb suite, while the Harker, Swinford, and Brownworth Plutons would not form part of any chemically coherent suite. This is analogous to the situation outlined by Whitten et al. (1987) who suggested numerous different suites can be defined depending on the combination of criteria selected. The lack of chemical coherence within these younger discordant plutons with Vanda felsic porphyry enclaves indicates amore complex petrogenesis than can beresolved by a simple suite-style approach. Throughout the remainder of this paper, only those plutons with field relationships and chemical characteristics consistent with the original defini- tion of the DV2 suite are referred to as DV2 suite granitoids. The Brownworth, Orestes, Swinford, and Harker Plutons are referred to individually, or as granitoids with apparently unique combinations of field relationships and chemical features. This approach is consistent with the implied complex petrogenesis of the younger granitoids, and is preferable to squeezing all these plutons into a single suite or defining multiple suites to accommodate individual plutons. 1000 500 • 200 100 - 50 :Rb • • „—• o 1 1 Syn-collisional Volcanic arc / 1 * Intraplate 10 20 50 100 Nb+Y o DV1a • DV1b x DV2 • Orestes Pluton • Brownworth Pluton + Harker Pluton - Swinford Pluton Fig. 7 Rb versus Nb+Y plot illustrating the depletion of the DV lb suite biotite granitoids and Orestes Pluton in Nb and Y relative to the DVla hornblende-biotite granitoids and the DV2 suite. The higher Rb content of the evolved DV2 suite granitoids relative to the DVla and DVlb suite granitoids is also apparent. Tectonic setting discriminant fields, after Pearce et al. (1984), are plotted for comparison. Data are from this study, Palmer (1987,1990), Allibone (1988), Smillie (1989), and Ellery (1989). Downloadedby[GNSScience]at17:3306December2015
- 11. 308 New ZealandJournal of Geology and Geophysics, 1993,Vol. 36 CORRELATION OF PLUTONS AND SUITES WITH PREVIOUSLY DESCRIBED GRANITOID UNITS IN SOUTHERN VICTORIA LAND Many previous workers in southern Victoria Land preferred to discuss the granitoids of the Dry Valleys area as large-scale units. These units are inferred here to be similar to suites of individual plutons, although they were commonly not defined as such (e.g., Gunn &Warren 1962;McKelvey & Webb 1962; Allen & Gibson 1962; Haskell et al. 1965a; Skinner 1983; Findlay 1985,1991). These large-scale units or suites include: the Pre-tectonic Gneisses, Larsen Granodiorite, and Irizar Granite initially proposed by Gunn & Warren (1962); Olympus Granite Gneiss, Dias Granite, Theseus Granodiorite, and Vida Granite initially proposed by McKelvey & Webb (1962); and the Kukri Hills, Larsen, and Victoria Intrusive Groups proposed by Findlay (1985). Some of these large-scale units were mapped throughout southern Victoria Land and the Wilson Terrane of northern Victoria Land (e.g., Larsen Granodiorite, Irizar Granite in Gunn & Warren (1962) and Skinner & Ricker (1968)). The internal makeup of these larger scale units is not discussed by many workers, although Gunn & Warren (1962) noted that the Irizar Granite defined by them consists of a number of separate plutons, whereas Skinner (1983) noted that the Larsen Granodiorite is a convenient name for a family of similar plutons. Sufficient detailed mapping has now been completed to allow an attempt at unravelling the relationships between suite nomenclatural schemes used by previous workers and this study. This discussion is an addition to the similar discussion in Smillie (1992), made necessary by the recognition of the DVla and DVlb suites here. The larger concordant plutons included in the DVla suite here were initially included in the Pre-tectonic Gneisses of Gunn & Warren (1962) and the Dias Granite and Olympus Granite Gneiss of McKelvey & Webb (1962) and Allen & Gibson (1962). The relatively small leucocratic Catspaw Pluton, also included in the DVla suite here, has previously been described as Irizar Granite by Haskell et al. (1965a). Subsequent workers have described the major plutons within the DVla suite as Larsen Granodiorite (Haskell et al. 1965a; Skinner & Ricker 1968; Skinner 1983) or members of the Larsen Intrusive Group (Findlay 1985, 1991). Gneissose margins of the Bonney, Wheeler, Cavendish, and Denton Plutons were included in the Larsen Intrusive Group by Findlay (1985), but hornblende-biotite orthogneisses, inferred here to be genetically associated with these plutons, were included in the Kukri Hills Group by Findlay (1985). Plutons included in the DVlb suite here were initially described as grey granite by, amongst others, Ferrar (1907) and Mawson (1916), and later named Larsen Granodiorite by Gunn & Warren (1962). However, subsequent workers (e.g., Haskell et al. 1965a; Skinner &Ricker 1968) applied the name Larsen Granodiorite to plutons here included in the DVla suite. These and subsequent workers have included DVlb suite in either the Vida Granite (Allen & Gibson 1962), Irizar Granite (Haskell et al. 1965a), or Victoria Intrusive Group (Findlay 1985). The DV2 suite and plutons with distinct chemistries, but identical field relationships, were initially described as Irizar Granite (Gunn & Warren 1962;Haskell et al. 1965a) and Vida Granite (McKelvey & Webb 1962; Allen & Gibson 1962), along with other plutons here included in the DVla and DVlb suites. Most recently, Findlay (1985) included rocks, here described aspart of the Brownworth Pluton, in the Briggs Hills Granodiorite, a suite scale subunit of the Larsen Intrusive Group. Other rocks that form part of the Pearse Pluton were not assigned by Findlay (1985) to any particular unit. Many of the individual plutons from each of the three suites of granitoids identified here have in the past been assigned to all the major granitoid units used by previous workers. This reflects the superficial similarity of many of the plutons in each of the three suites. Geochemical analysis during this study has sometimes indicated that granitoids initially assumed to be related on the basis of similar hand- specimen characteristics are unrelated plutons forming parts of genetically distinct suites (e.g., Catspaw and Pearse Plutons). Furthermore, the DVla and DVlb suites are inferred to be time transgressive, with emplacement of constituent plutons spanning at least the later stages of deformation in the adjacent Koettlitz Group (Cox & Allibone 1991). The time- transgressive nature of the suites defined here differs from the approach of previous workers who have attempted to distinguish the older granitoids partly on the basis of their inferred timing of emplacement relative to folding phases within the Koettlitz Group (e.g., Skinner 1983;Findlay 1985, 1991). This earlier approach tends to mask the genetic relationships of the various plutons and has the potential to separate genetically associated granitoids emplaced at differ- ent times into different suites, and combine genetically distinct plutons emplaced at the same time in the same suite, thereby confusing the petrogenetic interpretation of these granitoids. As a result of this study, we suggest that future workers record the shape and internal characteristics of individual plutons, rather than just summarise their observations by interpreting larger scale units, as has occurred in the past. Chemical analyses can then be related back to individual plutons with clearly defined field relationships, rather than interpeted suites that may contain unrelated plutons. Given the repeated inclusion of genetically unrelated plutons in the following previously defined, larger scale granitoid units, we would recommend that they be abandoned or confined to plutons in their respective type areas: Olympus Granite Gneiss, Larsen Granodiorite, Irizar Granite, Vida Granite, Dias Granite, Briggs Hills Granodiorite, Larsen Intrusive Group, Victoria Intrusive Group, Kukri Hills Group, and Theseus Granodiorite. CORRELATION WITH NORTHERN VICTORIA LAND Background geology Several recent papers provide sufficient analyses of granitoids (Borg et al. 1987; Vetter & Tessensohn 1987; Ghezzo et al. 1987; Armienti et al. 1990) from northern Victoria Land to allow a comparison with the chemistry of granitoids from the Dry Valleys area, and thereby test correlations made by earlier workers (e.g., Gunn & Warren 1962; Skinner & Ricker 1968). Potential correlatives of granitoids from the Dry Valleys area are those in the westernmost Wilson Terrane of northern Victoria Land (Stump et al. 1983). Bowers Terrane island arc tholeiites (Weaver et al. 1984; Bradshaw et al. 1985) juxtaposed against the eastern margin of the Wilson Terrane are considered to be allochthonous to the Antarctic Craton margin. Bradshaw et al. (1985) suggested accretion of the Bowers Terrane against the Antarctic Craton margin c. 500 Ma ago, postdating emplacement of Cambro-Ordovician Downloadedby[GNSScience]at17:3306December2015
- 12. Allibone et al.—Geochemistryof granitoids, Antarctica 309 Q" 40 60 ANOR 80 100 o DV1a • DV1b x DV2 Mt Abbott Intrusives (MAI) I ' I I J South Victoria Land Intrusives (SVLI) Fig. 8 Normative compositions of Dry Valley granitoids plotted in terms of the Q' and ANOR parameters after Streckeisen & LeMaitre (1979). Evolutionary trends of the southern Victoria Intrusives (SVLI) and the Mt Abbott Intrusives (MAI) of northern Victoria Land, after Armienti et al. (1990), are plotted for comparison. DV1 a and DVlb granitoids exhibit a similar trend to the SVLI of northern Victoria Land. The DV2 suite is characterised by a more "syenitic" evolutionary trend than either the SVLI or MAI. sg, syenogranite; mg, monzogranite; gr, granodiorite; ton, tonalite; qs, quartz syenite; qm, quartz monzonite; qmd, quartz monzodiorite; qd, quartz diorite; sy, syenite; mo, monzonite; md, monzodiorite; di, diorite. "Granite Harbour Intrusives" in northern Victoria Land, but predating emplacement of the Devonian Admiralty Intrusives in all terranes of northern Victoria Land. Both Borg et al. (1987) and Vetter & Tessensohn (1987) mapped dominantly two-mica S-type granites in the western part of the Wilson Terrane and gabbroic to granitic I-type granitoids in the eastern part of the Wilson Terrane. An active continental margin setting for the observed plutonism was inferred by both Borg et al. (1987) and Vetter & Tessensohn (1987), with the chemical data of Borg et al. (1987) suggesting increasing involvement of metasedimentary material in the granitoid source rocks towards the western part of the Wilson Terrane. Presumably, subduction ceased immediately to the east of the Wilson Terrane at c. 500 Ma with accretion of the adjacent Bowers Terrane. Unlike Borg et al. (1987) and Vetter &Tessensohn (1987), Ghezzo et al. (1987) noted significant amounts of I-type granitoid cropping out in the southern and western parts of the Wilson Terrane, indicating that the distribution of S-type and I-type granitoids is more complex than suggested by Borg et al. (1987) or Vetter & Tessensohn (1987). Armienti et al. (1990) identified two batholiths comprising three distinct I- type plutonic complexes of differing petrographic and chemical character in the Wilson Terrane of northern Victoria Land. In the southern part of northern Victoria Land, Armienti et al. (1990) described the "South Victoria Land Intrusives" (SVLI), which were inferred to be the northern extension of granitoids cropping out in the Dry Valleys area. The SVLI range in composition from diorite to leucogranite and include the granitoids of the Mt Larsen and Cape Irizar areas, which have previously been correlated with granitoids in southern Victoria Land (Larsen Granodiorite, Irizar Granite of Gunn & Warren 1962 and Skinner & Ricker 1968). To the north and east of the SVLI, the Wilson Terrane is intruded by the gabbroic to monzogranitic Deep Freeze Range Intrusives (DFRI) and the syenogranite-dominated Mt Abbott Intrusives (MAI) (Armienti et al. 1990). The DFRI and MAI in the north and east of the Wilson Terrane (Lantermann Terrane of Bradshaw et al. 1985) are separated from the SVLI in the south and west of the Wilson Terrane (Daniels Terrane of Bradshaw et al. 1985) by the Priestley Fault (Armienti et al. 1990), equivalent to the Soza Fault of (Bradshaw et al. 1985) and the Rennick-Aviator Line of Grew et al. (1984). The Priestley or Soza Fault corresponds to achange inthe metamorphic history of the older metasedimentary rocks (Grew et al. 1984). Grew & Sandiford (1984, 1985) indicate schists hosting the DFRI east of the Soza/Priestley Fault contain assemblages indic- ative of metamorphic pressures in excess of 6 kbar. Grew et al. (1984) and Vetter & Tessensohn (1987) described assem- blages indicative of peak metamorphic pressures of c. 4 kbar west of the Priestley/Soza Fault in rocks that host the SVLI. Correlation The apparent petrographic similarity of the SVLI and granitoids of the Dry Valleys area, long recognised by previous workers (e.g., Gunn & Warren 1962), indicates the SVLI are the most likely correlatives in northern Victoria Land of the Dry Valleys granitoids. The MAI are also compared with granitoids from the Dry Valleys, as their syenogranite composition is similar to the DV2 suite. Normative compositions of granitoids from the Dry Valleys are plotted and compared to the SVLI and MAI of northern Victoria Land (Armienti et al. 1990) in Fig. 8 (after Streckeisen & LeMaitre 1979). The DVla and DVlb suites show a similar evolutionary trend to the SVLI of northern Victoria Land, ranging in composition from monzodiorite and quartz-diorite through quartz-monzodiorite and granodiorite, to monzogranite. However, the evolutionary trend of the DV2 suite from syenite and monzonite through quartz-syenite to syenogranite is distinctly more "syenitic" than the evolu- tionary trends of either the SVLI or MAI. Therefore, the DV2 suite does not appear to have any geochemical counterparts in either the MAI or the SVLI of northern Victoria Land. Granitoids from the Dry Valleys area are compared further with the SVLI and MAI of northern Victoria Land in Harker diagrams (Fig. 9). The Harker diagrams suggest a similarity between the less evolved parts of the SVLI and the DVla suite of the Dry Valleys area. However, the SVLI analyses of Armienti et al. (1990) show significant scatter into the DVlb field, which is consistent with the presence of biotite granitoids in the SVLI (Armienti et al. 1990) similar to the DVlb suite. So-called "Irizar Type" evolved granitoids, described by Armienti et al. (1990), within the SVLI do not show any affinity with the DV2 suite from the Dry Valleys area, despite their similar appearance in hand specimen. Rather, granitoids from the Cape Irizar area of northern Victoria Land appear similar in chemical character to the evolved DVla suite Catspaw Pluton. Comparison of the MAI with the Dry Valleys granitoids indicates a weak similarity to the DV2 suite, although evolutionary trends on the Harker diagrams do not generally overlap. The limited data available indicate that the DVla suite in the Dry Valleys area could be a southern extension of the Downloadedby[GNSScience]at17:3306December2015
- 13. 310 New ZealandJournal of Geology and Geophysics, 1993, Vol. 36 3 • 65_._ 70 SiO2 CaO :X • . +•••-. 200- 100• 40 Volcanic arc granitoid intraplate To ' 20 40 60 i6< Nb+Y C ! ? DVIaSuite C t3 DV1b Suite •: :• DV2 Suite + o South Victoria Land Intrusives (SVLI) Ml Abbott Intrusives (MAI) Fig. 9 Harker diagrams com- paring the evolutionary trends of the DVla, DVlb, and DV2 suites in the Dry Valleys area (from Fig. 4) with the SVLI and MAI of northern Victoria Land. Analyses of the SVLI and MAI are taken from Armienti et al. (1990). The SVLI shows similar geochemical character to both the DVla and DVlb suites. The DV2 suite exhibits different evolutionary trends to either the SVLI or MAI, albeit with more similarities to the MAI than theSVLI. SVLI, with both "Larsen Type" and "Irizar Type" granitoids of Armienti et al. (1990) being represented by the DVla suite. However, further data are required to assess whether the DV1b suite also occurs in the SVLI of northern Victoria Land. No direct correlative of the DV2 suite appears to be present in the SVLI, as the "Irizar Type" granitoids of Armienti et al. (1990) display different evolutionary trends. This is an important conclusion because granitoids here included in the DV2 suite in the Dry Valleys area have previously been widely correlated with the granitoids of the Cape Irizar area in northern Victoria Land (e.g., Gunn & Warren 1962; Haskell et al. 1965a; Skinner & Ricker 1968; Skinner 1983). Furthermore, Vanda mafic and felsic dike swarms also appear to be absent from the SVLI of northern Victoria Land. Correlation of the SVLI of northern Victoria Land with the older granitoids of the Dry Valleys area is compatible with the metamorphic history of the host metasedimentary rocks. Koettlitz Group metasediments of the Dry Valleys area were inferred to have been metamorphosed at 700-750°C and 4-5 kbars (Murphy 1971;Allibone 1992; Cox 1992), similar to the metamorphic history inferred for the host rocks of the SVLI west of the Soza/Priestley Fault or Rennick-Aviator Line, but distinct from that inferred for the host rocks of the DFRI, east of the Soza/Priestley Fault (Grew & Sandiford 1984, 1985; Grew et al. 1984; Vetter & Tessensohn 1987; Talarico et al. 1987). CORRELATION WITH THE CENTRAL TRANSANTARCTIC MOUNTAINS McGregor (1965) and Haskell et al. (1965b) mapped a variety of granitoids including inferred pre-, syn-, and post-tectonic Downloadedby[GNSScience]at17:3306December2015
- 14. Allibone et al.—Geochemistryof granitoids, Antarctica 311 plutons within the Queen Maud Batholith of the central Transantarctic Mountains, south of the Dry Valleys. Sub- sequently, Borg (1983) noted a similar variety of granitoids, and subdivided these granitoids into S-types, more common in the western part of the Queen Maud Batholith adjacent to the Antarctic Craton margin, and I-types dominating the eastern part of the batholith. Haskell et al. (1965b) initially noted the petrographic similarity of some rocks in the Queen Maud Batholith and granitoids of the Dry Valleys area. Based on an interpretation of radiometric dates and this apparent petro- graphic similarity, Skinner (1983) suggested a correlation between the Carlyon Granodiorite (an integral part of the Queen Maud Batholith) and Larsen Granodiorite of the Dry Valleys area, here interpreted as partly equivalent to the DVla suite. However, Findlay (1991) noted that the Carlyon Granodiorite contains hypersthene and muscovite, unlike the Larsen Granodiorite/Intrusive Group, and questioned this correlation. More recently, Borg et al. (1990) described regional variations in the isotopic character of granitoids between the Nimrod Glacier and Gabbro Hills in the central Transantarctic Mountains, south of the Dry Valleys area. Cambrian- Ordovician granitoids in the westernmost Miller Range that intrude Precambrian metasediments forming the easternmost part of the Antarctic Craton are characterised by 87 Sr/86 Sr; in the range 0.73243-0.74174. Cambrian-Ordovician granitoids further to the east, between the Marsh Glacier and Shackleton Glacier, are characterised by lower initial 87 Sr/86 Sr; ratios in the range 0.70684-0.71906. Granitoids in the Gabbro Hills area east of the Shackleton Glacier are characterised by the lowest initial 87 Sr/86 Sri ratios of 0.70446-O.70589. These variations in isotopic character are consistent with the west- east change from S-type to I-type granitoids previously described by Borg (1983). Lack of published whole-rock analyses from granitoids of the Queen Maud Batholith prevents direct comparison with the chemistry of the DVla, DVlb, and DV2 suites of the Dry Valleys area. The lack of S-type granitoids in the Dry Valleys area is a fundamental difference, although similar rocks may be present beneath the ice cap to the west. Available Sr-isotope analyses from the Dry Valleys area (see discussion in Allibone et al. 1993a), including granitoids from the DVla, DVlb, and DV2 suites, exhibit a similar range of 87 Sr/86 Sr; to the granitoids cropping out between the Marsh and Shackleton Glaciers in the central Transantarctic Mountains. Borg et al. (1990) inferred the area between the Marsh and Shackleton Glaciers, referred to as the Beardmore Micro- continent, is allochthonous to the east Antarctic Craton, on the basis of the isotopic character of the Cambrian-Ordovician granitoids. Stratigraphic and intrusive relationships constrain the timing of accretion of the Beardmore Microcontinent to between 760 and 550 Ma (Borg et al. 1990). Granitoids cropping out between the Marsh and Shackleton Glaciers, with Sr-isotopic compositions similar to the Dry Valleys granitoids, were inferred to be derived from thinned Pre- cambrian continental crust (Borg et al. 1990). Additional Sr, Nd, and Pb isotopic data are required to adequately describe the granitoids of the Dry Valleys area and assess whether the crustal and tectonic model developed for the central Trans- antarctic Mountains by Borg et al. (1990) is applicable to the Dry Valleys area. The presence of at least three granitoid suites in the Dry Valleys area suggests considerable subtle complexity not yet recognised in the central Transantarctic Mountains area, or perhaps not present. PETROGENESIS, SOURCE CRITERIA, AND TECTONIC SETTING OF THE DVla, DVlb, AND DV2 SUITES Smillie (1992) inferred a subduction-related, continental arc setting associated with generation and emplacement of the DV1 suite, based on the characteristics of the DVla Bonney Pluton. Recognition of two fundamentally distinct DVla and DVlb suites, initially included in the DV1 suite of Smillie (1992), requires some reassessment of the source rocks and tectonic setting associated with emplacement of these rocks. Smillie (1992) inferred the younger DV2 suite was emplaced during postsubduction extension as a result of melting of I- type crustal material. It is possible that this occurred in response to emplacement of mantle-derived mafic rocks, perhaps represented by the shoshonites described by Keiller (1991), which crop out extensively throughout southern Victoria Land. Recognition of the geochemical complexity and conflicting chemical characteristics of the younger granitoids, with similar relative ages and enclave suites to those defined as members of the DV2 suite by Smillie (1992), requires reassessment of the petrogenesis of these younger granitoids as well. Source criteria and petrogenesis of DVla and DVlb suites Smillie (1992) clearly demonstrated the I-type characteristics of the DVla Bonney Pluton. This interpretation was based on the hornblende-clinopyroxene bearing assemblages, abun- dance of mafic enclaves, and relatively metaluminous, calcic, and sodic composition compared with S-type granitoids. The essentially identical characteristics of the other DVla granitoids described by Allibone et al. (1993a, b) and Cox & Allibone (1991) are also consistent with an I-type classi- fication. Rb, Sr, Na2O, K2O,and A12O3contents of these rocks are similar to those documented in Cordilleran I-type granitoids developed in volcanic arcs along continental margins (e.g., Atherton & Sanderson 1985). The DVlb suite is characterised by several features not typical of continental arc granitoids. These include the restricted compositional range, between 64 and 76 wt% SiO2, the extreme enrichment in Sr and to a lesser extent Na2O and A12C<3, and the extreme depletion in Y and Nb, while maintaining LREE contents comparable to typical I-type granitoids. This set of petrographic and geochemical features is not typical of either S-type or I-type granitoids as described by White &Chappell (1983).DVlb suite Sr,Na2O, andA12O3 contents are considerably higher and exhibit steeper negative correlations with SiO2 than typical Cordilleran I-type granitoids, similar to the DVla suite rocks (e.g., Atherton & Sanderson 1985), although these features are partly analogous to the chemistry of tonalites and trondhjemites (e.g., Manduca et al. 1992; Barnes et al. 1992). The high Sr content of the DVlb granitoids implies advanced melting of a dominantly quartzofeldspathic source in which plagioclase is not a residual phase. Alternatively, it may indicate a lesser degree of partial melting in a source rich in refractory minerals such as garnet and pyroxene, again where plagioclase is not a residual phase (e.g., Anderson & Cullers 1987, 1990; Tulloch & Rabone 1987; Manduca et al. 1992; Wyborn et al. 1992). Advanced melting of a quartzo- feldspathic protolith is consistent with the overall grano- dioritic composition of the DVlb suite. The extreme deple- tion in Y implies the presence of a refractory phase that Downloadedby[GNSScience]at17:3306December2015
- 15. 312 New ZealandJournal of Geology and Geophysics, 1993, Vol. 36 preferentially incorporates Y (and HREE) in the residual material, such as garnet. Lack of significant garnet within all but the most evolved DVlb granitoids would be consistent with only relatively minor residual garnet in a dominantly quartzofeldspathic protolith. Garnet present in the most evolved DVlb granitoids is inferred to have crystallised from the melt during emplacement, since the most evolved DVlb suite granitoids tend towards peraluminous compositions (also reflected in the presence of muscovite accompanying garnet). The source material for the DVlb suite must also be capable of producing a granitoid melt with an initial 87 Sr/86 Sr ratio around 0.708-0.709. This initial 87 Sr/86 Sr ratio is significantly higher than tonalitic and trondhjemitic rocks with superficially similar Sr, Na2O, and AI2O3 enriched chemistries, that are commonly inferred to have been derived by either partial melting, or fractional crystallisation of primitive basaltic material. Furthermore, the DVlb suite is significantly enriched in K2O and Rb compared to tonalitic and trondhjemitic rocks, which is reflected in the granodiorite and granite compositions. The restricted range of quartzo- feldspathic compositions implies the DVlb suite was derived from a similar relatively felsic, homogeneous source, rather than by fractional crystallisation of more mafic melts, which would produce dioritic and monzodioritic or tonalitic intrusives as well. Potential source rocks that could account for the character- istics of the DVlb suite include older, garnet-bearing, metaluminous granitoids or relatively immature meta- sediments. Melting of more mature sediments with pelitic compositions would give rise to granitoids with more typical S-type features, including peraluminous compositions and higher initial 87 Sr/86 Sr ratios. However, immature sediments containing relatively little material derived from old Archean and early Proterozoic sources could produce granitoid melts with bulk rock compositions and isotopic characteristics analogous to the DVlb suite. In order to account for the Y depletion, some garnet would need to be present in this metasedimentary protolith. Garnet and two-mica granodiorites and granites with chemistries similar to the DVlb suite have recently been described by Anderson & Cullers (1990) from the lower plate of the Whipple Mountain Metamorphic Core Complex. The grosssular-rich garnet compositions in these granitoids indicate crystallisation at pressures between 7.5 and 9 kbars, indicative of arelatively deep level of emplacement. Anderson & Cullers (1990) inferred that these granitoids were derived during partial melting of calcic greywackes, derived from a continental margin volcanic arc, metamorphosed to refractory garnet and omphacite-bearing, eclogite fades assemblages. Partial melting of garnet-bearing, eclogite facies rocks was invoked to explain the unusually high Sr content and depleted Y content of these granitoids. This hypothesis is consistent with petrologic evidence of a deep level of emplacement. Similar hypotheses involving partial melting at extreme depths have been invoked to explain the analogous chemistry of granitoids described by Wyborn et al. (1992), Norman et al. (1992), and Williamson et al. (1992). However, none of these other studies describe direct petrologic evidence of a deep level during granitoid emplacement. An analogous model could be postulated to account for the geochemical characteristics of the DVlb suite. Volcanogenic sediment underplated along the west-dipping subduction zone inferred to have been associated with DVla plutonism is a potential source for the DVlb suite. However, unlike the Whipple Mountain Metamorphic Core Complex granitoids, there is no direct evidence of a deep level of emplacement or generation for DVlb plutonism. Instead, most of the geologic evidence appears to contradict such a model. Clinopyroxene grains in the DVlb suite Dun Pluton have Fe-rich salitic compositions, without any trace of Al or Na that would be expected if they had crystallised under relatively high pressures. Field evidence indicates that the younger DVlb plutons are discordant, with irregular intrusion breccias developed along their margins. This contrasts with the concordant margins typical of granitoids emplaced at deeper levels. Any inference that the DVlb suite was derived from melting of sediments or plutonic rocks metamorphosed to eclogite facies assemblages would have to be based solely on the Sr-enriched and Y-depleted chemistry of these rocks, rather than a combination of petrologic and chemical data as in the Whipple Mountain Metamorphic Core Complex (Anderson & Cullers 1990). Garnet development in meta- morphic rocks over a wide range of temperatures, pressures, and whole-rock compositions indicates that these chemical features need not be indicative of partial melting at extreme depths, provided all available plagioclase in the protolith is consumed during partial melting. What is clear is that the DVlb protolith was characterised by a distinct composition and mineral assemblage compared with the partly coeval DVla suite, which implies coeval melting of distinct source rocks in different parts of the crust and possibly upper mantle. Petrogenesis of the DV2 suite and the Harker, Swinford, Orestes, and Brownworth Plutons The different chemical characteristics of these individual plutons and the DV2 suite require explanation. Each of these individual plutons and others included in the DV2 suite are inferred to have broadly similar ages, and all contain microgranitoid enclaves identical to the Vanda felsic porphyry dikes. Given these similar field relationships, a correspond- ing similar, coherent geochemistry would be expected. Variation in the chemistry of these granitoids may be caused by several processes or combinations of processes. These could include melting of a chemically inhomogeneous source, different amounts of contamination possibly by older DVla and DVlb granitoids, or subtle differences in the amount of fractional crystallisation within individual plutons during emplacement. Any model proposed to explain the characteristics of these plutons, which involves contamination of an "end member" DV2 melt, comparable to the least evolved parts of the Pearse or Rhone Plutons (Smillie 1992), must account for the selective changes in the concentration of only some of the chemical parameters relative to the inferred "end member" DV2 melt. For example, the chemistry of the Harker and Swinford Plutons is largely consistent with the DV2 suite except for the low K2O and Rb contents. This indicates any contaminant in these two plutons has only affected these two parameters. In contrast, the Orestes Pluton exhibits chemical characteristics almost completely consistent with the DVlb suite. Furthermore, the lack of widespread, partially assim- ilated xenoliths in any of these younger plutons is difficult to reconcile with a contamination hypothesis. Alternatively, intrusion of DV2 suite granitoids may have been accompanied by partial melting of older DVla and DVlb suite granitoids, which were emplaced at deeper levels Downloadedby[GNSScience]at17:3306December2015
- 16. Allibone et al.—Geochemistryof granitoids, Antarctica 313 than those currently exposed in the Dry Valleys area. In this hypothesis, little interaction is inferred between the melt that crystallised to form the DV2 suite plutons and other melts that produced the Harker, Swinford, Orestes, and Brownworth Plutons. This is distinct from the contamination hypothesis, where incorporation of xenolithic material during emplace- ment is the process controlling the chemistry of the resulting granitoid plutons. Liquid-crystal fractionation, particularly in more felsic granitoids, is widely postulated as the cause of significant enrichment or depletion of granites in some incompatible trace elements (e.g., Champion & Chappell 1992). At high SiO2 contents, relatively small amounts of crystal fractionation can markedly affect the content of some trace elements. The evolved compositions of the Orestes and Harker Plutons, in particular, are consistent with liquid-crystal fractionation being an important control on the chemistry of these granitoids. Similar suites of granitoids with incoherent chemistries are mentioned by Wyborn et al. (1992), who referred to these rocks as "melt-rich" granitoids as opposed to "restite-rich" granitoids. Wyborn et al. (1992) suggested the distinctive compositions of individual plutons reflects the melt-rich character of these intrusions during their emplace- ment. This allows each intrusion to independently undergo crystal-liquid fractionation, resulting in distinct chemistries developing, despite similar ages and field relationships. A similar hypothesis could be invoked to explain the different chemistries of the younger granitoid plutons in the Dry Valleys area. This would imply that all the younger plutons are derived from the same source, and are closely related, which is consistent with their field relationships. The relative importance of crystal-liquid fractionation and melting of an inhomogeneous source cannot be currently determined. Each is potentially capable of explaining the variations in chemisty between these younger granitoids. Tectonic synthesis: evolving plutonism along the early Paleozoic Antarctic Craton margin Field relationships, geochemistry, and radiometric dating indicate several marked changes in the nature of granitoid plutonism in the Dry Valleys area. These changes in the character of granitoid plutonism are inferred to reflect concurrent changes in the tectonic setting of the Cambrian- Ordovician Antarctic Craton margin. The earliest plutonism is dominated by the DVla suite with concurrent, but minor, DVlb plutonism. Given the similarity of the DVla suite to granitoids generated along continental margin arcs, a subduction setting is inferred at this time. Concurrent emplacement of small DVlb suite intrusions indicates minor melting of a distinctly different protolith. This protolith may have been small amounts of underplated metasediment derived from the arc associated with DVla plutonism. Termination of DVla suite plutonism was followed by emplacement of all the major DVlb suite plutons (Hedley, Valhalla, Suess, St Johns), marking a distinct change in the nature of granitoid plutonism along the early Ordovician Antarctic Craton margin. Radiometric dating of the St Johns Pluton indicates emplacement of this pulse of DVlb plutons occurred at 490 ± 14 Ma (Allibone et al. 1993a). The cause of this marked change in the style and chemistry of granitoid plutonism is unclear. However, it coincides with the inferred timing of accretion of the Bowers Terrane along the Antarctic Craton margin in northern Victoria Land (Bradshaw et al. 1985) at c. 500 Ma. Cessation of DVla plutonism in southern Victoria Land before c. 490 Ma, could indicate either a cessation of subduction altogether, or a radical change in the style of subduction. Cessation of subduction at this time in southern Victoria Land would be consistent with a similar accretion event. The pulse of DVlb plutonism emplaced at c. 490 Ma may reflect increased amounts of sediment underplated during such an accretion event, although this inference is highly speculative. Such an accreted terrane may now form the seafloor east of the current southern Victoria Land coast, along strike from the Bowers Terrane in northern Victoria Land. Clasts of volcanics and low-grade meta- sediment occurring in basal Devonian conglomerates of the overlying Beacon Supergroup throughout the Olympus and St Johns Ranges (Allibone et al. 1993b) have no obvious provenance in present-day southern Victoria Land. These rocks may be derived from this postulated allochthonous terrane. Emplacement of the DVlb suite was followed within 10 Ma or less by intrusion of the Vanda mafic dikes and associated felsic porphyry dikes. Keiller (1991) concluded that these were generated at the base of the crust by interaction of a mantle melt and a crustal component. Subsequent evolution was dominated by fractional crystallisation of alkali felspar. Field relationships indicate emplacement of the dikes was essentially contemporaneous with the beginning of DV2 alkali-calcic, Caledonian I-type magmatism. Analogous granitoids elsewhere are inferred to have developed in some type of extensional setting unrelated to subduction (Smillie 1992). Correlations inferred here suggest these later post- subduction granitoids and dikes do not occur in northern Victoria Land, indicating different Cambrian-Ordovician tectonomagmatic histories along the length of the Paleozoic Antarctic Craton margin between c. 486 and 450 Ma. SUMMARY AND CONCLUSIONS Chemical analyses of granitoids emplaced before the prom- inent Vanda mafic and felsic dike swarms in southern Victoria Land, indicate the existence of the distinct Dry Valleys la (DVla) and Dry Valleys lb (DVlb) suites. The DVla suite includes the batholithic-scale Bonney Pluton and at least four other major plutons of hornblende-biotite granitoid, as well as hornblende-biotite orthogneisses described by Cox & Allibone (1991). The DVlb suite includes several large plutons of biotite granodiorite and granite, and younger plugs of biotite granite (partly equivalent to the Theseus Granodiorite of McKelvey & Webb 1962), as well as biotite orthogneisses and the "Dun Type" orthogneisses of Cox & Allibone (1991). Field relationships indicate that emplace- ment of the older orthogneisses in both suites overlap, but the majority of DVla plutons, including the Bonney Pluton, predate emplacement of a major pulse of DVlb plutons. Radiometric dating indicates emplacement of the DVla and DVlb suites occurred before c. 490 Ma (Allibone et al.l993a). Younger granitoids emplaced after the majority of the Vanda mafic and felsic dike swarms, include the large Pearse and Nibelungen Plutons and other smaller bodies with chemistries analogous to the DV2 suite of Smillie (1992). Other relatively young granitoids (e.g., Orestes, Brownworth, Harker, and Swinford Plutons) were emplaced at the same time as the DV2 suite granitoids and contain identical felsic porphyry enclaves but they have variable geochemistries and Downloadedby[GNSScience]at17:3306December2015
- 17. 314 New ZealandJournal of Geology and Geophysics, 1993, Vol. 36 do not form part of a chemically coherent suite. DV2 granitoids and other plutons with analogous field relationships and enclaves, but different chemistries, were emplaced between c. 486 and 450 Ma. Comparison of granitoids from the Dry Valleys area with the "South Victoria Land Intrusives" of northern Victoria Land described in Armienti et al. (1990) indicates potential correlatives of the DVla and possibly DVlb suites. DV2 suite rocks from the Dry Valleys area, previously correlated with the evolved granitoids of Cape Irizar, are distinctly more monzonitic to syenitic in character. The only potential correlative of the Cape Irizar granitoids so far mapped in southern Victoria Land is the evolved DVla Catspaw Pluton. Sparse Sr-isotope data suggest granites of the Dry Valleys area are possible correlatives of granitoids cropping out between the Shackleton and Marsh Glaciers in the central Trans- antarctic Mountains (Borg et al. 1990). The geochemistry and abundance of mafic enclaves in the DVla suite plutons is typical of Cordilleran style I-type granitoids, and they are inferred to have developed above a subduction zone along an active continental margin. Chemical characteristics of the relatively leucocratic DVlb suite are more unusual. In particular, the very high Sr, A12O3 and Na2O contents, coupled with extremely low Y contents, indicate a source region lacking residual plagioclase, but containing garnet. Partly analogous granitoids elsewhere are inferred to have been derived from an eclogite fades protolith. However, no direct geologic evidence exists of such a source for the DVlb suite,other than the similar chemistry. The source of the DVlb suite granitoids is unclear although they may be derived from underplated volcanogenic sediments derived from the arc associated with DVla suite plutonism. The marked pulse of DVlb suite plutons corresponds to the timing of accretion of the Bowers Terrane in northern Victoria Land at c. 500 Ma and may reflect a similar accretion event in southern Victoria Land. The younger DV2 suite granitoids are analogous to Caledonian style I-type granitoids thought to be related to uplift and extension rather than subduction processes. The following speculative sequence of events is proposed to account for changes in the characteristics of granitoids along the Cambrian-Ordovician Antarctic Craton margin. Subduction-related Cordilleran style magmatism dominated before c. 500 Ma. At c. 500-490 Ma, Cordilleran type plutonism ceased and was replaced by a short pulse of DVlb plutonism characterised by Sr, Na and Al enriched, and Y depleted geochemistry, suggesting partial melting of garnet- bearing source rocks lacking residual plagioclase. These unusual granitoids may have been derived from sediment underplated along the subduction zone associated with Cordilleran plutonism. This pulse of DVlb suite plutonism may have developed in response to collision between an allochthonous terrane and the Antarctic Craton margin, marking the end of subduction-related plutonism. Later DV2 and related younger plutons are inferred to have been emplaced during postcollision uplift and extension, from c. 486 to 455 Ma. ACKNOWLEDGMENTS The authors thank D. Craw and R. D. Johnstone for their discussion and critical comments that considerably improved this paper. P. J. Forsyth, R. D.Johnstone, and M. Hunter are thanked for maintaining a sense of humour while crushing rocks and making XRF disks. S. Ness and A. Chappell are thanked for access to XRF facilities at JCU. In this paper we have drawn conclusions from data and observations of K. Palmer, I. J. Graham, I. G. Keiller, S. Ellery, R. J. Sewell, and I. M. Turnbull in addition to our own. Reviews by S. D. Weaver, J. D. Bradshaw, and R. H. Findlay resulted in considerable improvement to the paper. Fieldwork was made possible by The Ross Dependency Research Committee, Antarctic Division (DSIR) and VXE-6 squadron (U.S. Navy). REFERENCES Allen, A. D.; Gibson, G. W. 1962: Geological investigations in southern Victoria Land, Antarctica. Part 6: Outline of the geology of the Victoria Valley region. New Zealand journal of geology and geophysics 5: 234-242. Allibone, A. H. 1988: Koettlitz Group meta-sediments and intercalated orthogneisses from the mid Taylor Valley and Ferrar Glacier regions. Unpublished M.Sc. thesis, lodged in the Library, University of Otago, New Zealand. Allibone, A. H. 1992: Low pressure/high temperature metamorphism of Koettlitz Group schists in the Taylor Valley and Ferrar Glacier area, South Victoria Land, Antarctica. New Zealandjournal of geology andgeophysics 35: 115-127. Allibone, A. H.; Forsyth, P. J.; Sewell, R. J.; Turnbull, I. M.; Bradshaw, M. A. 1991: Geology of the Thundergut area, southern Victoria Land, Antarctica. 1:50 000 miscell- aneous series map 21 (with supplementary text). Wellington, New Zealand. Geology and Geophysics Division, Department of Scientific and Industrial Research. Allibone, A. H.; Cox, S. C.; Graham, I. J.; Smillie, R. W.; Johnstone, R. D.; Ellery, S. G.; Palmer, K. 1993a: Granitoids of the Dry Valleys region, southern Victoria Land, Antarctica: plutons, field relationships, and isotopic dating.New Zealandjournal of geology and geophysics 36: 281-297 (this issue). Allibone, A. H.; Heron, D. W.; Forsyth, P. J.; Turnbull, I. M. 1993b: Geology of the St Johns Range, southern Victoria Land, Antarctica. 1: 50 000 miscellaneous series map (with supplementary text). Lower Hutt, New Zealand. Institute of Geological and Nuclear Sciences. Anderson, J. L.; Cullers, R. L. 1987: Crust-enriched, mantle-derived tonalites in the early Proterozoic Penokean Orogeny of Wisconsin. Journal of geology 95: 139-154. Anderson, J. L.; Cullers, R. L. 1990:Middle to upper crustal plutonic construction of a magmatic arc; An example from the Whipple Mountains Metamorphic Core Complex. Geological Society of America memoir 174:47-69. Armienti, P.; Ghezzo, C.; Innocenti, F.; Manetti, P.; Rocchi, S.; Tonarini, S. 1990: Isotope geochemistry and petrology of granitoid suites from the Granite Harbour Intrusives of the Wilson Terrane, North Victoria Land, Antarctica. European journal of mineralogy 2: 103-123. Atherton, M. P.; Sanderson, L. M. 1985:The chemical variation and evolution of the super-units of the segmented Coastal Batholith. In: Pitcher, W. S.; Atherton, M. P.; Cobbing, E. J.; Beckinsale, R. D. ed. Magmatism at a plate edge: The Peruvian Andes. Glasgow, Blackie & Son Ltd. Pp. 208-227. Barnes, C. G.; Barnes, M. A.; Kistler, R. W. 1992: Petrology of the Caribou Mountain Pluton, Klamath Mountains, California. Jounal ofpetrology 33: 95-124. Borg, S. G. 1983: Petrology and geochemistry of the Queen Maud batholith, central Transantarctic Mountains with implications for the Ross Orogeny. In: Oliver, R. L.; James, P. R.; Jago, J. B. ed. Antarctic earth science. Canberra, Australian Academy of Science and Cambridge, Cambridge University Press. Pp. 165-169. Downloadedby[GNSScience]at17:3306December2015
- 18. Allibone et al.—Geochemistryof granitoids, Antarctica 315 Borg, S. G.; Stump, E.; Chappell, B. W.; McCulloch, M. T.; Wyborn, D.; Armstrong, R. L.; Holloway, J. R. 1987: Granitoids of northern Victoria Land, Antarctica: impli- cations of chemical and isotopic variations to regional crustal structure and tectonics. American journal of science 287: 127-169. Borg, S. G.; DePaolo, D. J.; Smith, B. M. 1990: Isotopic structure and tectonics of the central Transantarctic Mountains. Journal of geophysical research 95: 6647-6667. Bradshaw, J. D.; Weaver, S. D.; Laird, M. G. 1985: Suspect terranes and Cambrian tectonics in northern Victoria Land, Antarctica. In: Howell, D. G. ed. Tectonostratigraphic terranes in the Circum Pacific region. Circum-Pacific Councilfor Energy and Mineral Resources—earthscience series 1: 493-514. Champion, D. C.; Chappell, B. W. 1992: Petrogenesis of felsic I- type granites: an example from northern Queensland. Transactions of the Royal Society of Edinburgh earth sciences 83: 115-126. Cox, S. C. 1989: Gneiss geology—a structural perspective of foliated granitoids and their host rocks in the Wright Valley, South Victoria Land, Antarctica. Unpublished M.Sc. thesis, lodged in the Library, University of Otago, New Zealand. Cox, S. C. 1992: Garnet-biotite geothermometry of Koettlitz Group metasediments, Wright Valley, South Victoria Land, Antarctica. New Zealandjournal of geology and geophysics 35: 29-40. Cox, S. C. 1993: Inter-related plutonism and deformation in South Victoria Land, Antarctica. Geological magazine 130: 1-14. Cox, S. C.; Allibone, A. H. 1991: Petrogenesis of granitoid orthogneisses from the Dry Valleys region, south Victoria Land, Antarctica. Antarctic science 3: 405-417. Ellery, S. G. 1989: Lower Wright geology. Unpublished M.Sc. thesis, lodged in the Library, University of Otago, New Zealand. Ferrar, H. T. 1907: Report on the field geology of the region explored during the "Discovery" Antarctic expedition. National Antarctic Expedition 1901-04 natural history reports 1: 1-100. Findlay, R. H. 1985: The Granite Harbour Intrusive Complex in McMurdo Sound: progress and problems. New Zealand Antarctic record 6 (3): 10-22. Findlay, R. H. 1991: Antarctica. In: Nairn, A. E. ed. The Phan- erozoic of the World, Vol. A, The Palaeozoic. Amsterdam, Elsevier Publishing Company. Pp. 335-421. Ghezzo, C.; Baldelli, C.; Biagini, L.; Carmignani, L.; Di Vincenzo, G.; Gosso, G.; Lelli, A.; Lombardo, B.; Montrasio, A.; Pertusati, P. C.; Salvini, F. 1987: Granitoids from the David Galcier-Aviator Glacier segment of the Transantarctic Mountains, North Victoria Land, Antarctica. Geological Society of Italy memoirs 33: 143-159. Grew, E. S.; Sandiford, M. 1984: A staurolite-talc assemblage in tourmaline-phlogopite-chlorite schist from northern Victoria Land, Antarctica, and its petrogenetic significance. Contributions to mineralogy and petrology 87: 337-350. Grew, E. S.; Sandiford, M. 1985: Staurolite in a garnet-hornblende- biotite schist from the Lantermann Range, northern Victoria Land, Antarctica. Neues Jahrbuch fur Mineralogie Monatschefte, Heft. 9: 396-410. Grew, E. S.; Kleinschmidt, G.; Schubert, W. 1984: Contrasting metamorphic belts in northern Victoria Land, Antarctica. GeologischesJahrbuch. B 60:253-263. Gunn, B. M.; Warren, G. 1962: Geology of Victoria Land between the Mawson and Mulock Glaciers, Antarctica. NewZealand GeologicalSurvey bulletin 71. Haskell, T. R.; Kennett, J. P.; Prebble, W. M.; Smith, G.; Willis, I. A. G. 1965a: The geology of the middle and lower Taylor Valley of southern Victoria Land, Antarctica. Transactions of the Royal Society of New Zealand 2: 169-186. Haskell, T. R.; Kennett, J. P.; Prebble, W. M. 1965b: The geology of the Brown Hills and Darwin Mountains, southern Victoria Land, Antarctica. Transactions of the Royal Society of New Zealand 2: 231-248. Keiller, I. G. 1991: Wright dikes—a geochemical study of dike- forming rock types within the Wright Valley, Southern Victoria Land, Antarctica. Unpublished M.Sc. thesis, lodged in the Library, University of Otago, New Zealand. McGregor, V. R. 1965: Geology of the area between the Axel Heiberg and Shackleton Glaciers, Queen Maud Range, Antarctica. Part 1: Basement complex, structure and glacial geology. New Zealandjournal of geology and geophysics8: 314-343. McKelvey, B. C.; Webb, P. N. 1962: Geological investigations in Southern Victoria Land, Antarctica. Part 3: Geology of Wright Valley. New Zealand journal of geology and geophysics 5: 143-162. Manduca, C. A.; Silver, L. T.; Taylor, H. P. 1992: 87 Sr/86 Sr and18 O/ 16 O isotopic systematics and geochemistry of granitoid plutons across a steeply-dipping boundary between con- trasting lithospheric blocks in western Idaho.Contributions to mineralogy andpetrology 109:355-372. Mawson, D. 1916: Petrology of rock collections from the mainland of southern Victoria Land. Report of the British Antarctic Expedition 1907-09 geology 1:201-237. Murphy, D. J. 1971:The petrology and deformational history of the basement complex, Wright Valley, Antarctica, with special reference to the origin of augen gneisses. Unpublished Ph.D. thesis, lodged in the library, University of Wyoming. 114p. Norman, M. D.; Leeman, W. P.; Mertzman, S. A. 1992:Granites and rhyolites from the northwestern USA: temporal variation in magmatic processes and relations to tectonic setting. Transactions of the Royal Society of Edinburgh earth sciences 83: 71-81. Norrish, K.; Chappell, B. W. 1977: X-ray fluorescence spectrometry. In: Zussman, J. ed. Physical methods in determinative mineralogy. 2nd ed. London, Academic Press. Pp. 201-272. Norrish, K.; Hutton, T. J. 1969: An accurate X-ray spectrograph method for the analysis of a wide range of geological samples. Geochemica et cosmochimica acta 33:431-453. Palmer, K. 1987: XRF analyses of granitoids and associated rocks from southern Victoria Land, Antarctica. Victoria Universityof Wellington Research School of EarthSciences GeologyBoard of Studiespublication 3. Palmer, K. 1990: XRF analyses of granitoids and associated rocks, St Johns Range, south Victoria Land, Antarctica. Victoria Universityof Wellington Research School of EarthSciences Geology Board of Studiespublication 5. Pearce, J. A.; Harris, N. B. W.; Tindle, A. G. 1984: Trace element discrimination diagrams for the interpretation of granitic rocks. Journal ofpetrology 25:956-983. Priestley, R. E. 1914: Glaciology, physiography, stratigraphy and tectonic geology of south Victoria Land. British Antarctic Expedition 1907-09, reports on the scientific investigations, geology 1:244-247. Skinner, D. N. B. 1983:The granites and two orogenies of Southern Victoria Land, Antarctica. In: Oliver, R. L.; James, P. R.; Jago, J. B. ed. Antarctic earth science. Canberra, Australian Academy of Science and Cambridge, Cambridge University Press. Pp. 160-163. Downloadedby[GNSScience]at17:3306December2015
- 19. 316 New ZealandJournal of Geology and Geophysics, 1993, Vol. 36 Skinner, D. N. B.; Ricker, J. 1968: The geology of the region between the Mawson and Priestley Glaciers, northern Victoria Land, Antarctica. Part 1: Basement meta- sedimentary and igneous rocks. New Zealand journal of geology and geophysics 11: 1009-1040. Smillie, R. W. 1989: Granite Harbour Intrusives from the Taylor Valley and Ferrar Glacier region, southern Victoria Land, Antarctica. Unpublished M.Sc. thesis, lodged in the Library, University of Otago, New Zealand. Smillie, R. W. 1992: Suite subdivision and petrological evolution of granitoids from the Taylor Valley and Ferrar Glacier region, south Victoria land. Antarctic science 4: 71-87. Smith, W. C. 1924: The plutonic and hypabyssal rocks of southern Victoria Land, Antarctica. BritishAntarctic ("TerraNova ") Expeditions 1910-13 natural history report geology 1: 167-227. Streckeisen, A. 1976. To each plutonic rock its proper name. Earth science reviews 12: 1-33. Streckeisen, A.; LeMaitre, R. W. 1979: A chemical approximation to the modal QAPF classification of the igneous rocks. Neues Jahrbuch fur Mineralogie Abhandlungen 136: 169-206. Stump, E.; Holloway, J. R.; Borg, S. G.; Lapham, K. E. 1983: Bowers graben and associated tectonic features across northern Victoria Land, Antarctica. Nature 304: 334-335. Talarico, F.; Memmi, I.; Lombardo, B.; Ricci, C. A. 1987: Thermobarometry of granulite-rocks from the Deep Freeze Range, North Victoria Land, Antarctica. GeologicalSociety of Italy memoirs 33: 131-141. Tulloch, A. J.; Rabone, S. D. C. 1987: Geochemistry of molybdenum-bearing granodiorite porphyries in west Nelson with special reference to Eliot Creek, Karamea Bend and Taipo Spur. In: Proceedings of the 21st annual conference, New Zealand Branch, Australasian Institute of Mining and Metallurgy. Vetter, U.; Tessensohn, F. 1987: S- and I-type granitoids of North Victoria Land and their inferred geotectonic setting. GeologischeRundschau 76:233-243. Weaver, S. D.; Bradshaw, J. D.; Laird, M. G. 1984:Geochemistry of Cambrian volcanics of the Bowers Supergroup and implications for early Paleozoic tectonic evolution of northern Victoria Land, Antarctica. Earthandplanetaryscience letters 68: 128-140. White, A. J. R.; Chappell, B. W. 1983: Granitoid types and their distribution in the Lachlan fold belt, south east Australia.In: Roddick, J. A. ed. Circum Pacific plutonic terranes. Geological Society of America memoir 159:21-34. Whitten, E. H. T.; Bornhorst, T. J.; Li, G.; Hicks, D. L.; Beckwith, J. P. 1987: Suites, subdivision of batholiths and igneous- rock classification: geological and mathematical concept- ualization. Americanjournal of science 287: 332-352. Williamson, B.J.;Downes, H.;Thirlwall,M.F. 1992:The relationship between crustal magmatic underplating and granite genesis: an example from the Velay granite complex, Massif Central, France. Transactions of the Royal Society of Edinburgh earth sciences 83: 235-245. Wyborn, L. A. I.; Wyborn, D.; Warren, R. G.; Drummond, B. J. 1992: Proterozoic granite types in Australia: implications for lower crust composition, structure and evolution. Transactions of theRoyalSocietyofEdinburghearth sciences 83: 201-209. Downloadedby[GNSScience]at17:3306December2015