Petrogenesis of gneisses and granitoids from Southern Bastar Craton, India: A geochemical insight to crustal evolution

Abstract

This study investigates the geochemical evolution and petrogenesis of gneisses and granitoids from the southern part of the Bastar Craton, India, to understand the crustal evolution. The study incorporates the result on major, minor, trace and rare earth elements (REE) interpretation. The gneisses, classified as high alumina granodiorite to granite, peraluminous and exhibit geochemical signatures typical of Archaean TTGs, including enrichment in large ion lithophile elements (LILE) and depletion in high field strength elements (HFSE) with notable negative anomalies in elements like Nb, P, and Ti. In contrast, the granitoids show a meta-aluminous to per-aluminous composition, with higher K₂O/Na₂O ratios and pronounced enrichment in LILE with higher Sr, Ba, Zr, Nb, Y and Yb contents than the gneisses. These patterns suggest a progressive geochemical evolution from gneiss to granitoids. The study put forward two distinct subduction phases contributing to the formation of these rocks. The initial phase associated with a pre- to syn-collisional tectonic setting in a flat low-angle subduction at shallower depth and minimal interaction between slab melts and the mantle wedge. Whereas, the later one is characterized by a collision to subduction transition in a post-collisional setting with gradual increase in mantle-wedge interaction at a relatively greater depth, involving a steeply dipping subduction process. This dual-phase subduction model highlights the tectonic shift in the region over time and provides a comprehensive understanding of the geological evolution of the Bastar Craton.