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Dharwar Craton
The document provides information on the Dharwar Craton located in southwest India. It discusses the classification of the craton into the Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC). Key differences between the WDC and EDC are noted, including larger greenstone belts in the WDC surrounded by older gneiss, compared to narrower greenstone belts in the EDC intruded by a Dharwar Batholith. The lithology of the cratons is also summarized, including the Sargur Group, Bababudan Group, Chitradurga Group, and younger granites like the Closepet Granite. Regional structures, met
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Dharwar Craton
- 1. PRESENTED BY: VISHAKHA NATHANI M.Sc.GEOLOGY 1
- 2. Dharwar Craton– introduction and its extension Classification Difference between WDC and EDC Western Dharwar Craton Eastern Dharwar Craton Lithology Dharwar supracrustal rocks Sargur Group Bababudan Group Chitradurga Group Greenstone belts Younger granites Closepet granite Regional structure Metamorphism Life Economic importance of dharwarian rocks Summary Reference CONTENT 2
- 3. INTRODUCTION The Archaean DharwarCarton covering an area of about 4.5 lakh (0.45 million) km2 , the available geochronological ages spanning between 3.4 and 2.0 b.y.a. highlights the major early Precambrian events in the Craton and The term Dharwar (Karnataka) Craton was introduced by the geological survey of India in 1978.. The Dharwar Craton is one of the best-studied terrains of Peninsular India, and is renowned for its greenstone/schist belts, grey gneisses, charnockites and younger granites. It is bounded to the south by the Pan- African Pandyan mobile belt (PMB); to the north by the end- Cretaceous Deccan Trap underlain and fringed by the Proterozoic (Purana) Kaldgi and Bhima basins. 3
- 4. The contact betweenWDC and EDC is not sharp, and there is a transition zone between the Chitradurga Shear Zone and Closepet Granite. Chitradurga Shear Zone marks the boundary between Western Dharwar and Eastern Dharwar Craton apart from Closepet Granite The Chitradurga Shear Zone is a narrow geosyclinal belt which extends from Gadag in the north to Shrirangapatna in the south, for a length of 460 km. The belt attains a maximum width near Chitradurga . 4
- 5. ESSENTIAL FEATURES OF DharwarCraton DISTRIBUTION OF CRATONS 5
- 6. CLASSIFICATION The classificationhas been given by J. Swami Nath, M. Ramakrishnan and M. N. Viswanathan in 1976 resulted in a holistic stratigraphic model which was backed by a 1:500,000 scale geological map published in 1981. Essential features of this classification (Swami Nath and Ramakrishan 1981) are the following (Table 3D-2) Dharwar Craton was divided for the first time into two tectonic blocks WDC and EDC. {Ramakrishnan and R. Vaidyanadhan (2010) vol I geology of India PG NO 103} 6
- 7. WESTERN DHARWAR CRATON WDCis located in southwest India. Western Dharwar Craton (WDC) is occupied by vast areas of Peninsular Gneiss along with two prominent super belts of Bababudan – Western Ghats- Shimoga and Chitradurga- Gadag belonging to the Dharwar Super Group. WDC is bounded by EDC in east, Arabian Sea in west, to the south by a transition into the southern-granulite terrain and the north is buried under younger sediments and the Cretaceous Deccan Traps. GORUR GNEISS is the oldest gneiss in WDC. It is a suite of trondhjemitic gneisses with associated tonalities and granodiorites (TTG) . Sargur Group of rocks have been deposited during 3130-2960 m.y.(3.1 – 2.9 by) . 7
- 8. DHARWAR SUPERGROUP Table 1:Regional stratigraphy of WDC (after Swami Nath and Ramkrishnan 1981) Proterozoic mafic dyles Charnockites (2500-2600 Ma) Younger granites (2600 Ma) Ranibennuer Greywackes with BIF, polemic conglomerate, SubGroup mafic-felsic volcanic Manganese and iron formations, Mafic-felsic Stromatolitic carbonates, biogenic volcanic with Vanivilas cherts, pelites quartzite’s and BIF, phyllites SubGroup polymict conglomerates (basin center) (Basin Margin) Talya/Kaldurga Conglomerate= Metabasalt And siliceous phyllites of Jagar valley -----------------------------------------Disconformity---------------------------------------------------- Mulaingiri BIF with phyllites and rare ultramafic- mafic Formation Sills Santaveri Metabsalts, felsic volcanic (Galipuje felsites) Formation local BIF, phyllites, cross-bedded quartzite (Lakya) Kalasapura Metabasalts, gabbros, ultramafic schists Formation phyllites, quartzite’s, basal quartz pebble conglomerate (Kartikere conglomerate) ------------------------Deformed angular unconformity------------- 8
- 9. EASTERN DHARWAR CRATON TheEDC is bounded to the north by the Deccan Traps and the BastarCraton, to the east by the Eastern Ghats Mobile Belt, and to the south by the Southern Granulite Terraine . The Craton is composed of the Dharwar Batholith (dominantly granitic), greenstone belts, intrusive volcanics, and middle Proterozoic to more recent sedimentary basins. The supracrustal belts of the EDC are smaller in size than those of the western blocks which are surrounded by gneisses and granites. “older greenstone belts” that are either older or equivalent to the Bababudan Group of the western block. Metabasalts from Kolar schist belt indicating that they are contemporaneous with the Chitradurga Group of the western block (WDC). OLDER GNIESS: Recognizable areas of older gneisses are not widespread in the EDC in contrast to their extensive development in WDC. 9
- 10. TABLE 2, SIMPLIFIEDSTRATIGRAPHY OF ARCHAEAN DHARWAR CRATON {RAMAKRISHNAN AND R. VAIDYANADHAN (2010) VOL I GEOLOGY OF INDIA } PG NO 104 Age Western Dharwar Craton (WDC) Eastern Dharwar Craton (EDC) 2500-2600 Ma 2600-2800 Ma ~ 3000 ma 31000-3300 Ma 3300-34000 Ma Younger granite (Chitradurga, Arsikere) Charnockites Chitradurga Group Dharwar SuperGroup Bababudab Group ----- unconformity ---- Peninsular Gneiss Sargur Group Gorur Gneiss Younger granite/ gneiss (Close pet and equivalents) Charnockites Kolar Group Yashwantanagar Formation ----------------------------------- Enclaves of older gneiss (?) Warangal Group (?) Salem Group Putative Basement 10
- 11. Western Dharwar Craton(WDC) Eastern Dharwar Craton (EDC) 1. Dharwar schist belts-large, with volcanic , subordinate sediments 2. Peninsular Gneiss (>3000 Ma) basement having angular unconformity with the Dharwar marked by QPC. Basement gneiss inliers within schist belts. 3. Three fold succession of : (i) Basalt-arenite-BIF (ii) Shelf facies at the margin and homo axial pillowed basalt-BIF in deeper waters. (iii) Greywackes-BIF-volcanic 1. Older sequence (Sargur Group) as narrow belts and enclaves, abundant in the south 2. Intermediate pressure (Kyanite-sillimanite type) metamorphism 1. Dharwar greenstone belts-narrow, with dominant pillowed basalts 2. Dharwar Batholith (2500-2700 Ma) intrusive on all sides. Diapiric gneiss domes common 3. Three fold succession of: (i) Rare shelf sediments disrupted into screens at the belt margins. (ii) Pillowed volcanic, greywackes, BIF (iii) Felsic volcanic, volcanogenic conglomerate (‘Champion Gneiss’) 1. Older sequence (Warangal Group) mostly as enclaves in the northeast; and Salem Group(?) in the south 2. Low pressure (andalusite- sillimanite type) metamorphisam. Essential differences between Western Dharwar Craton (WDC) and Eastern Dharwar Craton (EDC) (Ramakrishnan and R. Vaidyanadhan (2010) vol I geology of India PG NO 100 ) 11
- 12. LITHOLOGY OF WDC Based on the supracrustal lithological relationship between the Peninsular gneiss and the supracrustal rocks, Swami Nath and Ramakrishnan (1981) classified the supracrustal rocks of DharwarCraton into older Sargur Group and younger Dharwar SuperGroup: SARGUR Group Age of Sargur is tentatively considered to be 3.4-3.0 b.y. Sargur Group found as belts enclaves ,narrow bands and stringers near Sargur town, situated 40 km southwest of Mysore city . Sargur Group lithology include quartzite, quartz fuchsite-muscovite schists, bedded barites sillimanite-garnet-staurolite-kyanitegraphite-corundum-quartz- biotite schists, crystalline limestone, dolomites, calcsilicate rocks, amphibolite (metabasaite), iron stones (oxide and silicate facies BIF) meta ultramafic and anorthosites. The Sargur enclaves represent: 1. elongated and locally faulted synformal keels and 2. antiformal hinges 12
- 13. YOUNGER DHARWAR SUPERGROUP The Dharwar supracrustal is deposited unconformably over a sialic basement of tonalitic and granitic “Peninsular Gneiss” (Chadwick et al., 1981). The supracrustal rocks of Dharwar Supercrustal are exposed as number of schist belts; prominent among them are: Bababudan, Western Ghat, Chitradurga, Shigegudda, Shimoga-North Kanara-Goa, Sandur, Kolar & Hutti schist belts. Total thickness of these Dharwar schist belts is estimated to be 6 to 7 km . Age of the Dharwar SuperGroup -3.0-2.6 b.y.a. 13
- 14. BABABUDAN GROUP BababudanGroup of rocks are exposed mainly in Bababudan, Western Ghats, Shigegudda and Yadiyur-Karighatta arm of Chitradurga schist belt. Bababudan Group represents a typical mafic platformal association ending up in prominent iron ore (BIF) cycle. The Bababudan sediments and Volcanics suggest nearshore to and subaerial to shallow marine environment respectively (Chadwick et al., 1985). The rocks of Bababudan Group are metamorphosed upto lower amphibolites facies (garnet isograd) at the borders and green schist facies at the core portions. 14
- 15. CHITRADURGA GRANITE Elongatedlenticular body of late to post-tectonic granite. 60 km long and 15 km wide exposed near Chitradurga town. It is essentially biotite granite grading into granodiorite and quartz monzonite. The potassic type granite is also evolved. The granite has yielded well fitted Pb-Pb and Rd-Sr isochrones (~2600ma) and SIMS U-Pb zircon (~2610ma). Studies suggest the involvement of the gennesis basement in its genesis. 15
- 16. YOUNGER GRANITES INWDC Late to post-tectonic Dharwar granites (~26000 Ma) that denote crustal reworking in WDC. Other Granites are as follow Jampalnaikankote (J.N. Kote) Granite Arsikere and Banavara Granites Hosadurga Granite Chamundi Granite Alkali Granites and Syenite 16
- 17. EASTERN DHARWAR CRATON The contact between WDC and EDC is not sharply defined, although the Chitradurga Boundary Fault is taken as a convenient and conspicuous marker. OLDER GNIESS: Recognizable areas of older gneisses are not widespread in the EDC in contrast to their extensive development in WD Their mutual relation with the greenstone belts is a matter of debate. 17
- 18. GREENSTONE BELTS OFDHARWAR SUPER GROUP The EDC is Characterized by volcanic-dominated, sediment- impoverished and gold – rich greenstone belts, in contrast to those of WDC. These greenstone belts are engulfed on all sides by younger granitoids. They are popularly known as Easter greenstone belts because of their geographic position in the craton. The linear arrays of superbelts in the EDC are the following: Ramagiri- (Penakacherla –Sirigeri ) – Hungund superbelt Lolar-Kadiri-Jonnagiri-Hutti Superbelt Veligallu-Raichur-Gadwal superbelt 18
- 19. YOUNGER INTRUSION INEDC The plutonic belts enclose a few scattered younger intrusions joga granite occurring with in the Sandur belt contains fluorite and carbonate yields SHRIMP U Page of 2570 Ma. Koppel syenite is an elongate, wedged-shaped intrusion trending NE SW, which has steep bending in contact with host granite to the NW of Sandur belt. 19
- 20. CLOSE PET GRANITE The liner belt of Closepet Granite is having a length of nearly 500 kms and an average width of 20-25 Kms. They are the most prominent of the younger granite. close pet granite is a unique linear arcuate body consisting of diverse granitic type. The most characteristic rock type of this class is coarse-grained porphyritic granite with large-sized pophyroblasts of pink and grey potash feldspar. Grey and pink porphyritic gneisses are also very common. 20
- 21. REGIONAL STRUCTURE Thestructures of the Dharwar Super Group are dominated by a set of mainly open to tight upright synclines. Compressive deformation can be recognised. Their trends are variable and the plunge of their axes range from sub-horizontal to sub-vertical. 21
- 22. METAMORPHISM The SargurGroup of rocks is metamorphosed ranging from middle amphibolite facies in central Karnataka to upper amphibolite and granuliefacies in southern Karnataka There is progressive change of regional metamorphism from north to south in the Dharwar Craton and it is related to increase in grade of metamorphism to increasing depth of burial. Vishwanatha and Ramakrishnan reported two basic types of metamorphic facies. On the western side of Closepet granite an intermediate pressure, and on the eastern side, low pressure metamorphic assemblages were recognized. On the western side of Closepet granite an intermediate pressure, and on the eastern side, low pressure metamorphic assemblages were recognized. 22
- 23. LIFE No fossilshave yet been found from Dharwarian rocks. Mostly of them are sedimentary in origin. OVERALL STRUCTURE • EXTENSIVE FOLDING • FAULTING AND INTENSE METAMORPHISM. 23
- 24. ECONOMIC IMPORTANCE OF DHARWARIAN ROCKS The Archean Group of rocks, of which dharwars forms a very important sun Group are regarded as the most important economic mineral bearing Groups of India stratigraphy. Most of the economic minerals like those of iron, copper manganese,lead,zinc, and gold etc. have come from rocks which broadly belongs to Archean time but not coal and petroleum. As regards mineralization, 1. The western block is characterized by copper, iron and manganese mineralization, whereas 2. The Eastern Block is known for gold, iron and manganese mineralization. 24
- 25. SUMMARY The DharwarCraton is one of the best-studied terrains of Peninsular India, and is renowned for its greenstone/schist belts, grey gneisses, charnockites and younger granites. Dharwar Craton was divided for the first time into two tectonic blocks WDC and EDC. Dharwar ‘System’ in WDC was Grouped into two orogenic cycles separated in time viz., the older Sargur Group (3100-3300 Ma) and the younger Dharwar SuperGroup (2600-28000 Ma). Sargur and Dharwar successions are separated by deformed angular unconformities at Bababudan, Sigegudda, Jayachamarajapura (J.C. Pura) and Chatti Hosahalli. Elsewhere (Hole Narasipura Mayasandra), the two successions are folded together into parallelism during the younger Dharwar orogeny. In EDC, younger granitites dominate, with subordinate gneisses, together constituting the Dharwar batholiths. The batholiths intrudes wholesale the various units of Dharwar sequence (2600-2800 Ma) 25
- 26. The contactbetween WDC and EDC is not sharply defined, although the Chitradurga Boundary Fault is taken as a convenient and conspicuous marker The greenstone belts of EDC from linear arrays of what may be called superbelts or composite belts that extent underneath the Cuddapah basin. Close pet Granite does not belong to the linear array. No fossils have yet been found from Dharwarian rocks. Structure: extensive folding and faulting and intense metamorphism. 26
- 27. REFERENCES Ramakrishnan andR. Vaidyanadhan (2010) volume I Geology of India published by the geological society of India PB 1922 Gavipuram, (PP. 99-180). D.N. Wadia, Geology of India 4th add., Publ. by The Macmillian company ltd. Canada (PP. 60-70). Krishnan, M.S. (1982) Geology of India and Burma, C.B.S. Publ. and Distributors, Delhi. R.kumar (1981) Fundamental of Historical Geology & Statigraphy of India (PP 139-161). WWW.Shodhganga.com WWW.vedamsbooks.com 27
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