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

Content Provider	Springer Nature Link
Author	Dessai, A. G. Downes, H. López Moro, F. J. López Plaza, M.
Copyright Year	2008
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.
Starting Page	243
Ending Page	272
Page Count	30
File Format	PDF
ISSN	09300708
Journal	Mineralogy and Petrology
Volume Number	93
Issue Number	3-4
e-ISSN	14381168
Language	English
Publisher	Springer-Verlag
Publisher Date	2008-02-14
Publisher Place	Vienna
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Mineralogy Geochemistry
Content Type	Text
Resource Type	Article
Subject	Geophysics Geochemistry and Petrology

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