Geochemistry of Mesoproterozoic Mafic Volcanics of Bayana Basin, North Delhi Fold Belt: Constraints on Mantle Source and Magmatic Evolution

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.