A Note on the Mode of Eruption of the Deccan Trap Lavas with Special Reference to Kutch

Abstract

On the basis of detailed field mapping and available gravity data, certain conclusions regarding the mode of eruption of Deccan trap lavas are drawn.

In Kutch, the Deccan trap formation outcrops along the western and southern periphery of the mainland. The trap flows which rest disconformably over the Mesozoic rocks, are also seen to cover the eroded Mesozoic structures. They thin out towards the central and northern hills of folded Mesozoic rocks. Whereas basic dykes and sills are concentrated in these fold zones, a number of plugs occur close to the Deccan trap outcrops. Igneous plugs, seem to be related more to the trap than the tectonism. The dykes and sills are probably syntectonic whereas the trap flows are post-tectonic with respect to the Mesozoic folding. Three volcanic cone-like structures have also been discovered at the fringe of the Deccan trap outcrop, near Jada and Wehar. It is therefore, concluded that the trap lavas in Kutch have mainly erupted from Hawaiian type shield volcanoes. The lavas erupted from such volcanic centres periodically and flowed to the south down the paleoslope towards the main volcanic field.

Positive gravity anomalies are noted around well known plugs of Saurashtra which have long been considered as the eruptive centres along tectonic lines. Similar anomalies which could also be interpreted as the subsurface volcanic plugs or cones, are seen within the major rift zones of Western India like Cambay and Narmada grabens and faulted west coast. Thus, the Deccan trap lavas of Peninsular India too might have erupted from Hawaiian type shield volcanoes situated along the major fracture zones.