Geochemistry and petrogenesis of granitoids around the Kolar Schist Belt, South India: constraints for the evolution of the crust in the Kolar area

Abstract

The Peninsular Gneiss surrounding the N-S trending Kolar Schist Belt in the Dharwar Craton includes several components of granitic rocks that range in composition from tonalite to granite. On the west, the different phases are referred to as the Dod, the Dosa, and the Banded Gneiss and the Patna Granite. The gneisses on the east are dominantly of one type and are referred to as the Kambha Gneiss. The Champion Gneiss occurring within the eastern part of the belt is compositionally similar to the plutonic Dod Gneiss and probably represents a near surface intrusion. Late aplites are present on both sides of the belt. The Banded Gneiss was formed by partial melting of tonalitic rocks, and the aplites were formed by the action of aqueous fluids during amphibolite-grade metamorphism. Excepting these two rocks, all other granitoids seem to have been formed from silica oversaturated parent magmas derived from LILE enriched mantle sources by fractionation processes including liquid immiscibility and fractional crystallization. In the Kolar area, therefore (1) the granitoids are not genetically related to the amphibolites of the belt, which require depleted mantle sources and (2) rocks derived from different mantle sources and probably at different times could have been subsequently brought together by tectonic processes.