Mineral Chemistry, Sr–Nd Isotope Geochemistry and Petrogenesis of the Granites of Bathani Volcano-Sedimentary Sequence from the Northern Fringe of Chotanagpur Granite Gneiss Complex of Eastern India

Abstract

New geochemical, mineral chemical, Sr–Nd isotope data of the granites from Bathani Volcano Sedimentary sequence (BVSs) from northern margin of Chotanagpur Granite Gneiss Complex of Central Indian Tectonic Zone has been presented in this paper to understand its petrogenesis and implications for crustal growth in the eastern Indian shield. Petrographically, they are coarse-grained granites with biotite, plagioclase feldspar and K-feldspar as major constituent phases with minor presence of muscovite. Granites are silica rich (62.42–71.08 wt%), high-K, calc-alkaline and peraluminous in nature. Trace element wise they show an overall enriched large ion lithophile elements (LILE) pattern with negative anomalies for Ba, Nb, Sr, P, Eu, Ti and Zr. They are characterized by fractionated REE patterns with enrichments in LREE relative to HREE and display pronounced negative Eu anomalies. The granites presents a lower (143Nd/144Nd)i values varying from 0.51130 to 0.51164 with εNd(t) values varying from 2.21 to −4.96 and low (87Sr/86Sr)i (0.705–0.711) and relatively old depleted mantle model age of TDM1 1886–2517 Ma. The emplacement age of the BVSs granites took place at ~1600 Ma as revealed by whole rock Rb–Sr isochron age. Interpretation of the observed data indicates that they are I-type granite related to arc magmatism and is the product of partial melting of a pre-existing metabasic crust due to heat generated by an underplating basaltic magma pool coupled with extensive fractional crystallization of plagioclase, biotite and K-feldspar during emplacement.