Olivine compositions in picrite basalts and the Deccan volcanic cycle

Abstract

Olivine phenocryst compositions and whole-rock chemical compositions are used to identify primitive picrite basalts from widely separated parts of the Deccan flood basalt province. Overall, primitive picrites constitute a significant volume of rocks within the province. Most were probably emplaced along 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 basalts at Paliad, Anila, Pawagarh, Kawant and Ambadongar to help delineate the petrogenesis of these mafic rocks, and we also examine the nature and probable origin of picrite basalts from other regions of the Deccan, such as the Western Ghats. The combined data suggest that the incidence of high-MgO lavas decreased with time during the Deccan volcanic cycle.