Petrographic study of Khajamalai Outcrop, Trichy

PETROGRAPHIC STUDY OF
KHAJAMALAI OUTCROP
BY,
POONTHENDRAL. T.K,
5YMSGL201611,
3RD YEAR MSC.GEOLOGY(INTEGRATED),
DEPT. OF GEOLOGY.

It’s a branch of Geology which deals with
classification and description of rocks.
AIM & OBJECTIVE
 To understand the petrographic study of
Khajamalai Outcrop in detail
PETROGRAPHY:

Geological Setting of Tamilnadu
 The state of Tamil Nadu is the southernmost part of India and lies
between 8º00’ to 13º13’N latitude and 76º15’ to 80º18’E longitudes.
 Tamil Nadu covers approximately 130,000km2 which is
approximately 4% of total area of India.
 According to geological features Tamilnadu can be divided into
three major zones viz.
1. Northern block,
2. Central block and
3. Southern block.
The Geological map of Tamil Nadu is shown in Figure 1.1.

Fig 1.1 Geological setting of Tamilnadu

Study Area
• The selected study area Khajamalai, Tiruchirappalli lies between
10º46’ 39"N to 78º41’13"E and is located at The Madurai block in
Tamil Nadu.
• The Eastern region of Tamil Nadu consists of massive Charnockites
and Enderbites .
• Field geological mapping has been carried out marking lithology
and field structural elements, such as foliation, dip, plunge of
lineation deformation surfaces and other.
• Our study area comes under the Madurai block or Madurai
granulite block of the southern granulite terrain of early Archean to
late Neoproterozoic.

FIELD EVIDENCES IN KHAJAMALAI OUTCROP
STRUCTURAL EVIDENCES :
 Fold
Anticline and syncline fold structure is seen (Fig 1.3 )
 Intrusion
Quartz veins are seen in large no. in that outcrop (Fig 1.4 )

EQUIPMENTS USED :
 Hammer and Chisel – For breaking the rock sample from the
exposure
 Primary Rock Cutter – For cutting the obtained rock sample
into smaller pieces
 Rock Grinding Machine – For reducing the thickness of the
rock sample to required thickness
 Glass plate – For refined polishing at final stage of thin
section preparation
 Carborundum powder – As an abrasive

 Hot plate – For heating the thin section sample
 Precision (secondary) cutter – To cut the unwanted
portions from the thin section
 Canada balsam – For pasting the rock sample with
the glass slide
 Polishing grinder – For the final polishing of the
sample

Samples collected
Rock is cut
Polished and Grind
Thin section done
Microscopic Study
METHODOLOGY :

THIN SECTION PREPARATION
 A big rock sample is cut into small rectangular pieces using a primary cutter.
 Samples are made into chip form and is grinded to make a smooth surface.
 The first step involves cutting the massive rock pieces into smaller ‘Chips’.
We use the precision cutting instrument .
 The sample obtained from the study area has to be studied in detail. For this
purpose we need to transform them as rock thin sections so that we can
analyze rocks on basis of petrology and mineralogy.
 A thin section is a 30μm (= 0.03 mm) thick slice of rock attached to a glass
slide with epoxy. Typical thin section slides are 26 mm x 46 mm, although
larger ones can be produced. They are generally covered by another glass
slide, a cover slip also attached to the rock with Canada balsam. The Canada
balsam ideally has an index of refraction of 1.55.

 To grind the sample, we use Carborundum powders of 80, 300 and 1000
ASTMs.
 The sample is kept in a hotplate for few minutes at 150 degrees.
 Canada balsam is carefully applied to the slide and the sample is attached
to the polished side. Care should be taken to avoid bubbles.
 The sample is rubbed over a glass plate with fine-grained abrasive until it
becomes transparent.
 Now the thin section is ready to be studied under a peterological
microscope.

PETROGRAPHY :
 The essential minerals of this rock are:
 Quartz – Under plane polarized light they are colourless in thin section. Often
contain inclusion. Under crossed nicol, exhibit first order yellow interference color
cleavage is absent. Relief is low with weak birefringence. It exhibit undulose or wavy
extinction. In this rock quartz were found be deformed and a resultant exhibits
elongation of the mineral along the gneissic foliation.
 Orthoclase – Under plane polarized light they are colorless in thin section, two
directional cleavage, low relief. Under crossed nicol, exhibit first order grey
interference color, weak birefringence, Inclined extinction 12º.
 Hypersthene – Under thin section pale green in color, Pleochroism from greenish to
dark green in color, two directional cleavage, high relief and weak birefringence.
Yellow to red of the first order interference color, parallel extinction.

The accessory minerals are:
Biotite
Garnet
Hornblende

The collected samples show equigranular texture, presence of minerals
such as hypersthene, quartz, feldspar as a major minerals and Biotite is
present as accessory minerals. The petrography reveals that the rock is
CHARNOCKITE.
ORIGIN OF THE ROCK
Charnockite is an metamorphic rock which crystallize under the high
temperature and pressure . Many Charnockite are considered to be the
result of crystallization from melts at relatively high temperatures.
RESULT

REFERENCE :
 M. Santosh, T. Tsunogae and S. Koshimoto (2004), First reports of sapphirine-bearing rocks
from the Palghat-Cauvery shear zone system, southern India, Gondwana Research., 7,620–
626
 Bhaskar Rao, Y.J., Chetty, T.R.K., Janardhan, A.S., Gopalan, K., 1996. Sm-Nd and Rb- Sr
and PT history of the Archean Sittampundi and Bhavani layered meta- anorthosite complexes
in Cauvery shear zone, South India:evidence for Neoproterozoic reworking of Archean crust.
Contributions to Mineralogy and Petrology..
 Ishwar-Kumar, C, Windley, B.F., Hone, K., Kato, T., Hokada, T., Itaya, T., Yagi, K.,
Gouzu, C, Sajeev, K., 2013, A Rodiman suture in western India: new insights on lndia
Madagascar correlations. Precambrian Research, 236, pp. 227-25 1.
 Sajeev, K., Windley, B.F., Connolly, J.A.D., Kon, Y., 2009.Retrogressed eclogite (20
kbar,1020 °C) from the Neoproterozoic Palghat–Cauvery suture zone, southern India.
Precambrian research
 Ghosh, J.G., deWit, M.J. and Zartman, R.E. (2004) Age and tectonic evolution
Neoproterozoic ductile shear zones in the southern granulite terrain of India, with
implications for Gondwana studies.Tectonics, v. 23, pp. 1-38.

REFERENCE :
 Kelsey, D.E., White, R.W., Holland, T.J.B., & Powell, R. (2004) Calculated phase equilibria in
K2O–FeO–MgO–Al2O3–SiO2–H2O for sapphirine–quartz bearing mineral assemblages. Journal
of Metamorphic Geology 22, 559-578.
 Meert, J.G. (2003) A synopsis of events related to the assembly of eastern Gondwana.
Tectonophysics, v. 362
 Qorri ana, Durmisi Cercis, Prifiti Irakli, Fociro Oltion, 2017 Mineralogy and Petrography of
Terrigenious formation in Brari Section, Albania. Pg no.33
 J.A. McKervey, 2005 Petrographic analysis of igneous and metamorphic rocks from the
fishguard, South Wales Pg.no 16
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Petrographic study of Khajamalai Outcrop, Trichy

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