Palaeoproterozoic Mafic magmatism in the Indian Shield: Petrologic, Geochemical and Thermal constraints on Proterozoic Mantle

Abstract

In this paper we have synthesized the published and unpublished geochemical data on the Palaeoproterozoic mafic magmatism in the Indian Shield. Palaeoproterozoic mafic magmatism is widespread in the Indian Shield; it mostly emplaced as dyke intrusions within the cratons and south Indian granulite region and as intrusives/traps in the intra-cratonic basins and the Eastern Ghat Mobile Belt. Integration of the U-Pb ages with palaeomagnetic results identified at least four discrete Palaeoproterozoic igneous events at 2.36-2.37 Ga, 2.1-2.2 Ga, 2.0-2.1 Ga 1.89-1.99 Ga and probably two other events at about 2.4 Ga and 1.8 Ga. The Palaeoproterozoic magmatism across the Indian cratons seems geochemically monotonous and exclusively mafic and sub-alkalic tholeiitic basalt/basaltic andesite in composition with typical enrichment of large ion lithophile and light rare earth elements. Fractional crystallization is the dominant mechanism controlling the geochemical spectrum of the Indian Palaeoproterozoic magmas with little indications of crustal assimilation. Asthenosphere mantle is the major supplier of material for the Palaeoproterozoic igneous activity. Sub-Continental Lithosphere Mantle (SCLM) seems to be the major contributor for the enriched characteristics of the Palaeoproterozoic mafic magmas erupted in the Indian Shield. Thermal energy for the initiation of melting is likely contributed by mantle plumes although a passive rifting is not ruled out. Geochemistry of the Palaeoproterozoic mafic magmas in some way appears to have similarities to that of the end-Cretaceous Deccan basaltic magmas and do reflect plume-lithosphere interaction. The SCLM beneath the Indian Shield was possibly enriched by addition of fluids/melts of deep mantle origin. We suggest that the major segments of the Indian SCLM were generated at around 3 Ga coinciding with a major crustal building activity in the Indian shield.