Petrogenesis of phlogopite-pyroxenite from Southern India: Implications for the link between Proterozoic subduction- to rift-related arc magmatism

In this study, we investigate phlogopite-rich pyroxenite from a major terrain boundary, i.e., the interface of Nallamalai Fold Belt and Nellore schist belt, in southern India. Petrographic studies reveal that the clinopyroxenite is composed of clinopyroxene and phlogopite with subordinate pyrrhotite in which cumulus texture is conspicuously noticed. Resorbed grain boundaries noticed in the clinopyroxene indicates crystal melt interaction. The relatively high Mg# (61–67) supports the mantle derived nature of the pyroxenite. The negative Ta, Nb and Ti anomalies along with the Ca (a.p.f.u) and Ti (a.p.f.u) content of clinopyroxene, which indicate that the rock is emplaced in a subduction zone tectonic setting. The incompatible trace element ratios (Hf/Sm-Ta/LaN and Zr/Sm), involving high field strength elements, of these clinopyroxenite is also suggests the vital role of the H2O + CO2 rich fluid-related metasomatism. The pyroxenite of the study area is situated along two major tectono-magmatic arc-back arc domains i.e., Palaeoproterozoic (1.85–1.6 Ga) Kondapalli-Kandra Region (KKR) with subduction related island arc basalt-type setting and Mesoproterozoic (1.35–1.2 Ga) alkali basaltic magmas of Prakasam continental Rift-Zone (PRZ). The tectono magmatic signatures of the phlogopite-rich clinopyroxenite from the study area indicate a petrogenetic link between Palaeoproterozoic subduction related island arc magma and the Mesoproterozoic rift-related magmatism established along the margin of Eastern Dharwar Craton (EDC) and Eastern Ghat Belt (EGB) in Southern India.