Olivine compositions in picrite basalts and the Deccan volcanic cycle

Olivine phenocryst compositions and whole-rock chemical compositions are us ed to identify primitive picrite basalts from widely separated parts of the Deccan flood basalt province. Overall, primitive picrites constitute a sig nificant volume of rocks within the province. Most were probably emplaced a long deep faults in the Cambay graben and Narmada rift regions. We combine mineral composition data on previously described samples from boreholes at Dhandhuka, Wadhwan and Botad with information on new finds of picritic basa lts at Paliad, Anila, Pawagarh, Kawant and Ambadongar to help delineate the petrogenesis of these mafic rocks, and we also examine the nature and prob able origin of picrite basalts from other regions of the Deccan, such as th e Western Ghats. The combined data suggest that the incidence of high-MgO l avas decreased with time during the Deccan volcanic cycle.