Deccan basalts

Abstract

The Deccan basalts now cover an area of c. 500,000 sq. km in central and western India. The lava pile varies in thickness from c. 2000 metres in western India to c. 100-200 metres in central India, exposing the upper and lower horizons of the volcanics respectively. The salient mineralogical and chemical characters of the basalts are reviewed. Dominantly the basalts are tholeiitic while minor alkalic variants in western India represent the closing phase of volcanic activity. The diversification of the magma to the west is associated with thickening of the lava pile and increase of heat flow. The ultrabasic flows (picrite basalts) are products of fractionation of the source magma of olivine tholeiitic composition. The minor acid variants (e.g. rhyolites, pitchstones, felsites, etc.) are possibly residual liquids of the ascending magma.