Petrology and geochemistry of mafic plugs associated with the Semri Group of the Vindhyan Supergroup in the eastern part of the Son valley, Central India: Implications for bimodal volcanism

Abstract

The intrabasinal felsic pyroclastics and rhyolite in the lower part of Semri Group of Vindhyan Supergroup are intruded by 3-11 m thick mafic plugs. These mafic bodies intrude Kajrahat Limestone of Semri Group. Earlier studies pertaining to these dykes are restricted to petrography; however, geochemical data on these rocks are lacking. Ca-plagioclase, augite, and enstatite-bearing dolerites show sub-alkaline nature with basaltic andesitic (52-56% SiO 2 ) composition. They exhibit moderate incompatible trace elemental enrichment, characterized by enriched LREE and depleted HREE [(La/Yb) N = 3.5-5.7] contents akin to those reported from the intraplate continental rift-related basalts. Moreover, high Ba, Th, U together with the low Nb, Ta, and Ti values suggests crustal contamination. Chondrite-normalized REE patterns and trace element ratios when compared to continental rift basalts show similarity with them.Th/Ta and La/Yb discriminant diagram represents mixed sources and characterizes the occurrence in the sub-continental lithosphere. High La/Nb, La/Ta ratios, and positive Eu anomaly indicate that the basalt was derived from a depleted mantle source but mixed with crustal components. It is further supported by the ratios of Yb/Ta, Nb/Ta, and Zr/Hf indicating crustal contamination. In this article, we report the petrological and geochemical characteristics for the bimodal volcanics in order to understand their magma source and implications on tectonic setting in the lower part of Vindhyan Basin.