SEMINAR

ON

EASTERN DHARWAR CRATON

C0NTENTS INTRODUCTION

DHARWAR CRATON

EASTERN DHARWAR CRATON

STRATIGRAPHY OF EDC

GREENSTONE BELTS OF DHARWAR SUPERGROUP

CLOSEPET GRANITE

VERTICAL ZONATION OF THE CLOSEPET GRANITE

REGIONAL METAMORPHISM

CONCLUSION

REFERENCE

INTRODUCTION A large portion of a continental plate that has been

relatively undisturbed since the Precambrian era andincludes both shield and platform layers.

The word craton was first proposed bythe German geologist L. Kober in 1921 as "Kratogen",referring to stable continental platforms.

There are five Craton in Indian shield:-

Dharwar Craton

Bastar Ctaton

Singhbhum Craton

Aravalli craton

Bundelkhand Craton

TECTONIC MAP OF INDIAN SHIELD

DHARWAR CRATON Archean Dharwar Craton covers a total area of 4.5 lakh

sq.kms.

Bounded by Pan-African Pandyan Mobile belt (PMB)towards the south, Cretaceous Deccan traps towardsthe north, Proterozoic (Purana) Kaladgi and Bhimabasins, Neoproterozoic Eastern Ghats mobile belttowards (EGMB) toward east, Arabian sea towards thewest and Archean Karimnagar granulite belt (KGM)toward north east

It consists of the greenstone schists belts, charnokites,grey gneiss,quarzite, marble, BIF, and the youngergranites.

Divided into Eastern and Western Dharwar Cratonseperated by the Chitradurga Shear Zone.

STRATIGRAPHY

CLASSIFICATION OF EDC The component units are:

OLDER GNEISS: Older gneiss are not widespread inEDC, isolated U-Pb Zircon dates of over 3000 Ma areseen in some gneissic outcrops along the Western andEastern margin of Greenstone belts like Kolar and theRamagiri. (Putative basement).

WARANGAL GROUP: Lithologies mainly belong toquartzite–pelite-carbonate consisting of fuchsitequartzite, quartz pebble conglomerate, calc silicates,marble , cordierite -anthophyllite rocks, BIF.

o These suites are similar to that of Sargur Group but for thelesser development of mafic and ultramafic suites ,it isnamed as Warangal Group.

o Run parallel trends to those of Dharwar schist belts havingsimilar metamorphic and migmatic history.

GREENSTONE BELTS OF DHARWAR SUPERGROUP

EDC is characterised by volcanics-dominated, sediment-impoverised and gold rich greenstone belts, in contrast of WDC.

The greenstone belts are engulfed all sides by younger granatoids.

The Yeswantanagar Formation of the Sandur belts has similarity to that of Bababuddan Group intruded by granite.

Most of the greenstone belts are corelatable with that of the Chitradurga belt of WDC.

The greenstone belts of EDC form linear arrays and are called superbelts or composite belts-extends underneath the cuddapah Basin .

IMPORTANT GREENSTONE SUPERBELTS OF EDC :

Ramagiri (Penakachela-Sirigeri)-Hungund superbelt:-

Ramagiri-Penekacherla-Sirigeri Greenstone Belt, Hundgund Greenstone Belt

Kolar-Kadiri-Jonnagiri-Hutti superbelt:-

Kolar Greenstone Belt,Kadiri Greenstone Belt, Jonnagiri Greenstone Belt, Hutti Greenstone Belt

Veligallu-Raichur-Gadwal superbelt:-Veligallu Greenstone Belt, Raichur Greenstone Belt, Gadwal Greenstone Belt,

Sandur superbelt

Hutti Greenstone belt

Rich in gold mineralisation called as Hutti Maski beltwith southern extension to Siruguppaa

Cover an area of about 670 km2 consist of basicvolcanic suite, minor BIF in basic acidic volcanics,greywackes and polymict, granite-clast conglomerate.

The Hutti-Maski belt has a NNW-SSE trend with a

sharp hook shaped bend in the north towards SE.

The hook shape of the belt can be attributed to cross

folds and also to the diapiric nature of the two phases

of granatiod intrusions into the greenstone belt.

Kolar Greenstone Belt

Narrow linear schist belt intruded by diapric granitesof Patna and Bisanattam, and by granodioritic gneisseson all sides.

It consists of amphibolites, BIF, cordierite-silliminite-fuchsite quarzites, calc-sillicate rocks, manganiferouschert and carbonate.

The overlying pillowed, agglomeratic and varioliticamphibolites are essentially tholeiites.

INDEX

1. mafic rock

2. volcanoclastic sediments (champion gneiss)

3. Banded ferruginous chert

4. granite and gneiss

5. granitic pluton

Geological sketch map of Kolar Schist belt

CLOSEPET GRANITE It is a unique linear body consisting of diverse granitic

types. The granites have easterly convexity that mirrors the

configuration of the schist belts. Named after the town of Closepet, named for Major

Close, a British Army officer and now known asRamanagaram.

It is 200 km long and 20-30 km wide plutonic beltbounded by shear zones

High precision Zircon ages of granite from differentlaboratories define a narrow age of 2510-2530 Ma.

It is divisible into two parts-southern and the northernseparated near Kalyandurga by a Gap area.

The closepet granite is divided in to 3 depth zones 1.RootZone, 2.Transfer Zone, 3.Intrusion Zone with a gapzone.

VERTICAL ZONATION OF THE CLOSEPET GRANITE

REGIONAL METAMORPHISM It is of low-pressure facies series with typical pelitic

assemblages of andalusite-cordierite-staurolite inamphibolite facies grading into cordierite-garnet-silliminite-hypersthene in granulite facies.

Metamorphic P-T conditions of EDC range from670˚C/3kb in Sandur belt in the north, through710 ̊C/4-5 kb in the middle to 750̊C/6-7kb inKrishnagiri-Dharmapuri area.

Low pressure metamorphism of EDC is caused by theabundance of younger granite providing the advectiveheat, which was lack in WDC.

CONCLUSION Dharwar Craton is a classical greenstone-granite

terrain, divided into Western and Eastern DharwarCraton.

It is separated by the Chitradurga Shear Zone close tothe Closepet Granite.

EDC consists of the older gneisses, greenstone belts ofDharwar super group, Closepet Granite andcharnokites.

It is one of the best studied terrain of Peninsular India.

EDC is regarded as an Archean batholith that accretedon to the craton in the west along a diffuse zone ofinteraction

REFERENCE Geology of India by M.Ramakrishnan and R. Vaidyanathan.

Published by Geological Society of India: Vol.I, 2008 page:48-50, 99-180

WEB:

www.google.com:-

www.mindat.org/loc-49196.html

wikipedia.org/wiki/Dharwar_Craton