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

Kamal Kant Sharma ¹, M. Shamim Khan ², M. Raza ², M. Safdar-E-Azam ², G. Vallinayagam ³, M. Shamim Khan ², M. Raza ², M. Safdar-E-Azam ²

Affiliations
1 Government College, Sirohi- 307 00 1 (Rajasthan), IN
2 Dept. of Geology, Aligarh Muslim University, Aligarh - 202 003, IN
3 Department of Earth Sciences, Kurukshetra University, Kurukshetra - 136 1 19, IN

Abstract

No Abstract.

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M. Shamim Khan ¹, M. Raza ¹, M. Safdar-E-Azam ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh 202 002, IN

Abstract

Neoproterozoic Bombolai volcanics of Trans - Aravalli terrain of western Rajasthan, consist of three distinct flows separated by metasediments including bedded chert, phyllite and quartzite In terms of their major oxides and trace and rare earth element abundances, all these flows are compositionall identical and evolved (Mg No 0 397-0 474, Ni - 61-92 ppm and Cr - 172-234 ppm) Major and trace element contents permi one to classify them as subalkaine basalts having enriched LREE abundances However, MORB and PM- nomalised spidergrams characterize them as within plate tholeites On the basis of their TiO₂, content (1 84-2 43), Ti/Y ratio (294-347) and Zr/Y ratio (2 9-3 7), the Bombolai volcanics are classified as low Ti-continental tholentes The general geology geochemistry and associated lithologies indicate that the Bombolai volcanics were erupted in a reactivated nit environment (Pali lineament) which probably occurred as a precursor event to a large magmatic activity ie Malani volcanism in Trans-Aravalli region.

Keywords

Geochemistry, Continental Flood Basalts, Neoproterozoic, Tans-Aravallis, Pali District Rajasthan.

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M. Raza ¹, M. Safdar-E-Azam ¹, M. Shamim Khan ¹

Affiliations
1 Department of Geology, Aligarh Muslim University, Aligarh -202002, IN

Abstract

Mesoproterozoic volcanism in Bayana basin in the northeastern part of Aravalli-Delhi fold belt consists of mafic lava flows with quartzite-conglomerate intercalations. The volcanics are tholeiites, characterized by enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) and depletion of Nb, P and Sr. The values of TiO₂ (1.06 to 2.31 %), Zr (50 to 182 ppm), Ti/Y (286 to 521), and Zr/Y (2.63 to 5.70) are low, which illustrate their close similarity with low-Ti continental flood basalts. The Bayana volcanics may have been derived from an enriched mantle source with no significant crustal contamination. The parental magma appears to have been derived from a subcontinental lithospheric mantle source with Fe/Mg ratio exceeding that of model pyrolite. It is suggested that the mantle source of these volcanics was enriched through metasomatism by progressive transport of mantle fluids and/or melts from deeper mantle. Olivine and clinopyroxene dominated the fractional crystallization and played a major role in the evolution of magma, following its derivation from shallow mantle source(s) where clinopyroxene occurred as a residual phase.

Keywords

Geochemistry, Mafic Volcanism, Bayana Basin, Delhi Fold Belt, Proterozoic, Rajasthan.

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