Geochemical Signatures of Gneisses and Granulites of Marthandam, Tamil Nadu, India

Abstract

The Southern Granulite Terrain of South India is a collage of high grade granulite blocks and major transcrustal shear zones. The study area falls in the southern part of the Kerala Khondalite Belt. The area exposes a series of rocks which comprises of Garnet Biotite Gneiss (GBG), charnockite and pyroxene granulite along with intrusive syenite. Geochemically the gneisses are peraluminous showing an alkali- calcic affinity; while massive charnockites are peralkaline. The gneisses are having numerous patches of incipient charnockite that are peraluminous in nature. Generally it is inferred that strongly peraluminous magmas derived from mature pelitic sediments may produce S-type igneous rocks. The gneisses of the area are not so intensely peraluminous, discounting their being categorized as metapelitic. The source rocks are intermediate to felsic igneous rocks as well as products of partial melting of metaluminous mafic minerals. The gneisses of the Nagercoil massif falls in the within plate granite field (WPG) of Nb vs. Y and Rb vs. (Y+ Nb) plot. The present work is an attempt at constraining the geochemistry and tectonic environment of the gneisses and associated rocks of the Marthandam area