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Petrology and geochemistry of xenoliths in lamprophyres from the Deccan Traps: implications for the nature of the deep crust boundary in western India

Published online by Cambridge University Press:  05 July 2018

A. G. Dessai
Affiliation:
Department of Geology, Goa University, Taleigao Plateau, Goa 403 206, India
O. Vaselli
Affiliation:
Department of Earth Sciences, University of Florence, 50121 Florence, via G. la Pira, 4, Italy

Abstract

Alkaline lamprophyre intrusives from the western Deccan Traps (Murud-Janjira, south of Bombay) host rare lithospheric xenoliths and megacrysts. The xenolith suite consists of clinopyroxenites and granulites which show eclogitic affinities. The former have transitional (porphyroclastic to equigranular) textures whereas the latter are porphyroclastic, xenomorphic to meta-igneous. The textural features provide evidence of ductile-brittle deformation. The protoliths of the pyroxenite and granulite xenoliths were formed as cumulates of alkaline and sub-alkaline magmas respectively.

Mineral chemistry and geochemical data for the xenoliths bear testimony to the metasomatized nature of the deep crust. The xenolith data coupled with the geophysical evidence indicate that the lower crust beneath Murud-Janjira is dominated by mafic granulites and pyroxenites. The latter have under- and intra-plated the continental crust beneath the region.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1999

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