Alkaline Magmatism in the Deccan Volcanic Province

Alkaline magmatism in the Deccan volcanic province is characterised by i) relative spatial restriction, being manifested in the western and northwestern parts of the province, ii) development of alkaline rock assemblages in plug like bodies and hypabyssal minor intrusions, iii) alignment of magmatic activities along three (or four) volcanotectonic belts meeting near the gulf of Cambay, iv) pronounced fractional crystallisation of parent alkali basaltic magma often leading to wide spectrum of rock composition and v) relative rarity of effusive alkaline rocks.

The ultimate derivative of fractionating alkaline basic magma is usually a hypersolvus foid syenite. Alkaline ultrabasic rocks (melteigite-ijolite) in association with carbonatites are developed in a few plugs. Alkaline minor intrusions of wide compositional variation, are largely associated with subvolcanic plugs and a few volcano tectonic belts. In comparison, effusive alkaline rocks are rare in the province. Manifestation of alkaline lavas together with picritic basalts and spilite in western India reflect unique structural setting of this terrain.

Available petrological, geomorphological and geophysical data all point to a plume activity in the present Cambay region and this appears to be the major controlling mechanism for alkaline magmatism.