Flow-stratigraphy and geochemical variants of Bhadrajan volcanics, Jalore district, Rajasthan: Implications for a heterogeneous protolith

The Malani volcanics exposed in a curvilinear pattern around Bhadrajan are characterised by the presence of eight flows of rhyolitic to dacitic composition and have chemical characteristics similar to within plate, A-type granitic rocks. The pyroclastic unit present at the base of each flow marks the beginning of next pulse of discharge. The chemistry of Bhadrajan volcanics suggests two distinct rhyolite groups. Group 'A' is characterised by high Ca, Al, Na₂O/K₂O and low Rb, Th, La, Ce and Rb/Sr as compared to group 'B' rhyolites. The field and chemical data suggest a heterogeneous nature of protolith for Bhadrajan volcanics. The partial melting of igneous and siliceous metapelitic protolith could result in 'A' and 'B' group of rhyolites respectively.