Tectonic implication of geochemistry of gabbro norite basic granulite suite in the Proterozoic Delhi Supergroup, Rajasthan, India
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The granulitic terrain of Proterozoic Delhi Supergroup exposed between Balaram and Mawal in Gujarat carries a suite of plutonic basic intrusive rocks consisting of gabbro, norite and basic granulites. Chronologically the suite is younger than metabasic rocks of north and central Rajasthan and occurs as melt intrusion within the host of pelitic granulites, calc granulites and granite gneisses. The suite ranges in chemical composition from alkaline to tholeiite through calc alkaline with characteristic major elemental distribution. Rare earth element chemistry shows Eu anomaly with LREE and LILE enrichment over HREE and HFSE. On the basis of the above enrichment it is invoked that the rocks are possibly derived from an enriched mantle beneath a subduction zone. Further, the Hf/3-Th-Ta and Th/Yb-Ta/Yb systematics reflect a compositional match with calc alkaline basalt of present are setting. These lead to suggest that the gabbro-norite-basic granulite suite signifies continental are magmatism in Delhi Supergroup and the Aravalli mountain had been evolved through continental collision and subduction during upper Proterozoic time.
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