Petrology and Geochemistry of Xenoliths in Lamprophyres from the Deccan Traps: Implications for the Nature of the Deep Crust Boundary in Western India

A. G. Dessai1 and O Vaselli2
1 Department of Geology, Goa University, Taleigao Plateau, Goa 403 206, India
2 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 mafie granulites and pyroxenites. The latter have under- and intra-plated the continental crust beneath the region.

Keywords: xenoliths • lamprophyres • Deccan Traps • deep crust boundary

Mineralogical Magazine; October 1999 v. 63; no. 5; p. 703-722; DOI: 10.1180/002646199548862
© 1999, The Mineralogical Society
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