Lower crustal contamination of Deccan Traps magmas: evidence from tholeiitic dykes and granulite xenoliths from western India

Dessai, A.G. and Downes, Hilary and Lopez-Moro, F.J. and Lopez-Plaza, M. (2008) Lower crustal contamination of Deccan Traps magmas: evidence from tholeiitic dykes and granulite xenoliths from western India. Mineralogy & Petrology 93 (3-4), pp. 243-272. ISSN 0930-0708.

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Official URL: http://dx.doi.org/10.1007/s00710-007-0223-3

Abstract

Evidence for the nature of contaminants of Deccan Traps magmas may be provided by crustal xenoliths in lamprophyre and tholeiitic dykes that intruded the Deccan lava pile towards the end of volcanic activity. The potential contaminants are represented by xenoliths that include mafic (plagioclase-poor) granulites and felsic (plagioclase-rich) granulites. The granulites in general are peraluminous, light-rare-earth-enriched and have high Ba/Nb, very low Sm/Nd and Rb/Sr ratios. The protoliths of mafic granulites were mostly cumulates (high Mg#, low SiO2/Al2O3) of sub-alkaline magmas. The felsic granulites are metaigneous quartz-normative rocks and have relatively low concentration of Ba and Sr compared to the mafic types. The dykes consist of picritic basalts and two varieties of tholeiitic basalts, and in general show a complex mineralogy indicative of magma mixing. The picrites have primitive Mg#s, relatively high Nb, Zr, Sr, Ba and Ba/Y, with relatively low Nb/Zr and Nb/Y compared to the more evolved tholeiites. In terms of Sr-Nd isotope systematics the older (thol I) dykes are less contaminated compared to the younger ones (thol II). These characteristics are consistent with fractional crystallisation and mixing between evolved and primitive tholeiitic melts coupled with assimilation of lower crustal felsic granulites. Petrogenetic modelling indicates fairly high rates of contamination for mafic magmas with high abundances of both compatible and incompatible elements. Similar processes of lower crustal contamination may have resulted in production of two of the major Deccan Traps lava formations, the Poladpur and Mahabaleshwar Formations, which are geochemically analogous to the tholeiitic dykes.

Metadata

Item Type:	Article
School:	Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences
Depositing User:	Administrator
Date Deposited:	09 Feb 2011 14:03
Last Modified:	02 Aug 2023 16:51
URI:	https://eprints.bbk.ac.uk/id/eprint/1782

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