Petrogenesis of Pal Laharha granitic gneiss in Eastern Indian craton: Evidence from field relations and petrochemistry

Abstract

A large segment of the southcentral part of the Eastern Indian Craton proximal to the contact of the Eastern Ghats Mobile belt is occupied by the Pal Laharha gneiss. Spatially associated with the lithoensemble of greenstone belts. This segment is a zone of high strain traversed by regional faults. The granite gneiss is mainly represented by stromatic migmatite having supracrustal rocks constituting the immobile components. Three different varieties of granite VIZ (i) fine to medium grained mesocratic, horriblende-magnetite bearing granite, (ii) banded, pink, leucocratic granitic gneiss, and (iii) muscovite-biotite±garnet bearing medium to coarse grained granitic gneiss have been identified in this segment. The granitic gneiss has a granite to monzogranite range of composition and compares well with anorogenic, metalummous A-type granite (A/CNK<1). Highly fractionated REE, LREE enrichment, flat HREE pattern and a -ve Eu-Anomaly characterize the granites. From field, petrographic and geochemical attributes, it is suggested that the Pal Laharha granitic gneiss does not form a discrete plutonic body. It possibly evolved by the synkinematic mid-crustal anatexis of the supracrustal sequences now occuring either as megaenclaves or as immobile components.