TTG suite from the Bundelkhand Craton, Central India: Geochemistry, petrogenesis and implications for Archean crustal evolution

Abstract

The Bundelkhand Craton is one of the important Archean protocontinental nuclei in Peninsular India for which not much information on tectonic setting, evolutionary history and petrogenetic processes is available. Here we provide comprehensive geochemical data on the tonalite-trondhjemite-granodiorite (TTG) rocks which form the basement rocks for the craton. Compositionally, these rocks are variably evolved between diorite and granites, and display both high- and low-Al TTG types with geochemical features typical of convergent margin tectonic setting. The evolved granitoids are essentially low-pressure type, further grouped into sodic/“true TTG” and potassic/“transitional TTG” types. The low pressure and moderate-shallow depths of melting conditions, and low Mg#, Ni and Cr contents do not support a direct slab melting scenario. Alternately, these features favor the derivation of the BnGC granitoids through the melting of a sub-arc basaltic source possibly at the lower part of thickened arc crust in a suprasubduction regime. The occurrence of identical lithological assemblages in other cratons in Peninsular India, and similar petrogenetic conditions for the emplacement of TTGs suggest the involvement of subduction–accretion processes in building the ancient cratonic nuclei of the Indian shield.