Subduction related tectonic evolution of the Neoarchean eastern Dharwar Craton, southern India: New geochemical and isotopic constraints

Abstract

The Neoarchean eastern Dharwar Craton (EDC) is distinct from the Mesoarchean western Dharwar Craton (WDC) in many aspects of its geology. The important distinguishing features of the EDC are the predominance of younger granitoids, abundance of gold mineralization and the exposure at lower crustal depths. No consensus exists on evolutionary models for EDC; mutually exclusive plume and subduction-derived tectonic models have been proposed. Geochemical and radiogenic isotopic studies on the granitoids and volcanic rocks of three greenstone belts along a cross-section in the northern part of EDC are presented herein. The evolved Nd isotopic signatures, radiogenic Pb isotopic ratios and “arc-like” geochemical signatures are suggestive of a subduction regime and the involvement of recycled older crust in the derivation of these rocks. The proposed petrogenetic mechanism involves multi stage processes in a supra subduction regime involving slab dehydration, formation of hydrous basaltic melts, and re-melting and interaction with sub-arc basaltic crust at low pressures where amphibole±plagioclase is the dominant residual phase. There is a notable systematic decrease in the extent of older crustal involvement from west to east in the EDC. This is in concurrence with the younging of Dharwar Craton from west to east and eastward subduction. The proposed petrogenetic model can efficiently explain the variations in older crustal involvement, which is very common in other Archean cratons.