Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

Gurmeet Kaur ¹, P. K. Mehta ²

Affiliations
1 Centre of Advanced Study in Geology, Panjab University, Chandigarh - 160 01 4, IN
2 Department of Geology, Mohan Lal Sukhadia University, Udaipur, Rajasthan, IN

Abstract

The Jasrapura granitoid intrudes the rocks of Proterozoic Delhi Supergroup in the northern part of the Khetri Copper Belt (KCB), Rajasthan. It forms a lenticular sheet like body, exposed in the core of an NNE-SSW ) trending anticline formed by the Alwar feldspathic quartzite. Quartz, microcline, microcline-perthite, plagioclase and biotite are the main mineral constituents while titanite, magnetite, allanite and epidote occur as accessory minerals. The Jasrapura granitoid has been characterised as peraluminous, I-type, calc-alkaline granite with subordinate granodioritic component. Various petrological and geochemical parameters collectively indicate its fractionation-related petrogenesis from magma generated in the mantle wedge overlying the subduction zone. The calc-alkaline trend of evolution, high K₂O/Na₂O ratios, enriched incompatible trace elements (Rb, Ba, Th, U, etc), flat HREE profiles, low (La/Yb)_N, ratios and high Yb_N values of Jasrapura granitoid compare favourably with the post-Archaean arc granitoids. The trace element tectonic discrimination diagrams and spidergrams suggest an island arc tectonic regime for the Jasrapura granitoid.

Keywords

Jasrapura granitoid, Petrology, Geochemistry, Island Arc Tectonic Regime, Khetri Copper Belt, Rajasthan.

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Gurmeet Kaur ¹, P. K. Mehta ¹

Affiliations
1 Centre of Advanced Study in Geology, Panjab University, Chandigarh - 160 014, IN

Abstract

This is a preliminary report on the detailed petrological and geochemical investigations of Jasrapura, Gorwala and Gothara granitoids, intruding the rocks of Delhi Supergroup in the vicinity of Khetri town (28°00'N; 75°47'E). The field relationships of the granitoids, particularly their intertwinned and overlapping relationship with the mafic magmatic rocks, their common and typical accessory mineral assemblage, their I-type characteristics, and the major, trace and REE geochemistry, all point towards a common mafic magmatic source, fractionation-related petrogenesis and a complex island arc-marginal basin tectonic regime.

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