Influence of sources in the generation of silicic rocks of the Deccan Traps Continental Flood Basalt

Complex petrogenetic processes involving multiple sources may account for the presence of silicic rocks (SiO₂ >65 wt%) in Continental Flood Basalts (CFBs). Here, we use a holistic framework involving field observations, petrography, major oxides (n = 56), and trace element chemistry to examine eight scattered but significant silicic rock exposures found within the 65.5-66 Ma old Deccan Traps CFB. Rhyolite and granophyre with subordinate felsite, ignimbrite, trachyte, pitchstone and microgranite coexist with basalt, basaltic andesite, and gabbro. Thermodynamic-based Rhyolite-MELTS modelling suggests that the major oxide composition of associated basalt is a likely candidate for the parental melt composition of the silicic rocks of the Deccan Traps. Two broad REE patterns are noticed in the Deccan Traps silicic rocks; a flat pattern for Barda, Alech, and Chogat-Chamardi silicic rocks, and a steep REE pattern for Osham, Rajula, Pavagadh, Rajpipla, and Bombay silicic rocks. Basalt from Barda (La/Lu_N = 3.57) and Pavagadh (La/Lu_N = 11.0) display similar flat and REE patterns observed in the associated silicate rocks. Trace element modelling reveals that partial melting at different depths (shallow vs. deeper) from lherzolite sources and subsequent extensive fractional crystallization (50-90%) of these two parental mafic melts could generate the trace element composition of the Deccan Traps silicic rocks. The geochemical variability of Deccan Traps silicic rocks reveals an origin mostly from a mantle source with contributions of continental crust at a later stage, which is typical of silicic volcanism in other global CFBs.