Showing papers by "Arijit Ray published in 2012"
TL;DR: Paharpur gabbroic intrusive is an arcuate body running east-west paralleling the foliation of Chhotanagpur Granite Gneiss which acts as country rock.
Abstract: Paharpur gabbroic intrusive is an arcuate body running east–west paralleling the foliation of Chhotanagpur Granite Gneiss which acts as country rock. The main gabbroic body is intruded by a number of dolerite dykes running north–south. It is composed of clinopyroxene (Wo48En40Fs12–Wo51En40Fs09, mg no. 72–82), plagioclase (An52–An90), hornblende (magnesian hornblende to ferro-tschermackite), orthopyroxene (En76–En79) and ilmenite. Hornblende occurs as large poikilitic grain and constitutes around 60% of the rock. Both gabbro and associated dolerite dykes, show relatively primitive character (mg no. 65–73). Primitive mantle-normalized and MORB-normalized spider diagrams indicate enrichment in Rb, Ba, Th, La, Sr and depletion in Nb, Zr, Y, Ti and Nd. The LILE enrichment and Nb, Ti, Zr, Y depletion suggest arc like geochemical signature for the gabbroic and doleritic rocks of Paharpur. Flat to slightly LREE fractionated pattern and variable degree of REE enrichment is observed. An early stage fractionation of clinopyroxene, plagioclase, orthopyroxene, ilmenite and late stage reaction of cumulate pile and evolved melt/hydrous fluid is suggested for magmatic evolution of gabbro. Associated dolerite dykes, which are geochemically similar to the gabbro, have tholeiitic with boninitic character. The mineralogical and chemical compositions of intrusive rocks also have some similarity with mafic rocks of ophiolite complex of subduction zone.
20 citations
TL;DR: In this paper, the geochemical properties of Newer Dolerite dykes were investigated in the context of possible tectonic setting, and the authors made attempts to classify these dykes according to their trace and REE composition.
Abstract: Copyright © 2012 by The Geochemical Society of Japan. belong to different generations (Saha et al., 1973). The geochemical characters of these dykes are strikingly uniform over a long period of time (Bose, 2008; Mallick and Sarkar, 1994). Bose (2008) suggested that Newer Dolerite dykes generated through partial melting of subcontinental mantle which in turn was metasomatised. Mir et al. (2010) documented geochemical characteristics of these dykes similar to those of back arc extension basalts (BABB). In the studied area shear fractures which appears to act as pathways of these mafic intrusives have two dominant trends NE-SW and E-W and a subsidiary NW-SE trends. This might suggest that stress system have not an uniform direction over a long period, but it changed orientation with time. The geochemical classification of these dykes and their linking to possible tectonic settings have not yet been reported by earlier workers. In the present work, attempts have been made to classify these dykes according to their trace and REE composition. The genesis of different chemical types of Newer Dolerite dykes has been discussed in the perspective of possible tectonic setting.
9 citations