Early oceanic opening off Western India-Pakistan margin: The Gop Basin revisited

Abstract

The Deccan Traps, one of the best known examples of rapid flood basalt, are considered as marking of the inception of a mantle plume on the Indian continental lithosphere. Their emplacement may be associated with the continental break-up of India and the Seychelles block and later formation of a new spreading centre, the Carlsberg Ridge, while spreading progressively ceased in the Mascarene Basin. Whether rifting, continental break-up, and seafloor spreading predated or were the consequence of the Deccan Traps emplacement is still a matter of debate. This issue is further complicated by the presence of a continental sliver, the Laxmi Ridge, and large basins lying landward of the Laxmi Ridge, such as the Laxmi and Gop asins, where nature of the crust is still ambiguous. The present study attempts to decipher the tectonic setting and the imprints of plume-ridge interaction in the Gop Basin, where the crust has been interpreted as either volcanic-intruded thinned continental crust or oceanic crust formed by a now-extinct spreading centre. Based on interpretation of an updated compilation of marine geophysical data, the present study supports the oceanic nature of the crust underlying the Gop Basin and proposes the Palitana Ridge as the extinct spreading centre in this region. The prominent but short sequence of fairly linear magnetic anomalies in the Gop Basin does not allow a unique identification; it can be reasonably explained either as A31r-A25r (approx. 69.3-56.4 Ma) or as A29r-A25r (approx. 64.8-56.4 Ma) sequence. The variations of the spreading rates assumed by both these models suggest that spreading in the Gop Basin significantly slowed around 65 Ma, contemporaneous with the magmatic outburst of the Reunion plume on the adjacent western Indian mainland. Subsequently, the Gop Basin spreading centre was waning whereas a new spreading centre was developing further south, close to the (relatively) southward migrating plume. In this last stage, the Gop Basin spreading centre was associated with an abundant magmatism, probably supplied from the plume region