Petrological and Geochemical Characteristics of Archean Gneisses and Granitoids from Bastar Craton, Central India – Implication for Subduction Related Magmatism

The gneisses and granitoids of Bastar craton (with rock suites up to 3.5 Ga) show calc-alkaline trondhjemitic characteristics. The rocks are enriched in both LILE and HFSE than primordial mantle. They have also relatively higher abundances of LILE and strong depletion at P and Ti in the multielement diagram. The depletion of Ti and P indicates retention of these elements by titanite and/or apatite during partial melting. It is proposed that subduction of an oceanic slab and its consequent melting led to the formation of the protoliths of the gneisses without much interaction with the mantle wedge. The granitoids represent temporally distinct suites formed in response to further melting of slab at greater depth and interaction of magma with the mantle wedge during their transport to the crust.