Continental margin off Western India and Deccan Large Igneous Province

Abstract

Massive, transient late syn-rift-to-breakup volcanism during separation between the Seychelles microcontinent and India formed the Deccan continental flood basalts and their equivalents on the Seychelles-Mascarene Plateau and on the conjugate continental margins, i.e. the Deccan Large Igneous Province. We estimate an original extrusive area of at least 1.8×106 km2, and a volume >1.8×106 km3, and suggest a plate tectonic model comprising: (1) development of the Seychelles microplate by fan-shaped spreading in the Mascarene Basin, and continental extension followed by fan-shaped spreading between India and the Seychelles during A29-27 time. (2) Cessation of fan-shaped spreading just after A27 time, followed by spreading along the India-Seychelles plate boundary. (3) Margin subsidence, modified south of Goa by the persistent, time-transgressive effects along the plume trail. The margin is divided into three regional provinces by the prolongation of regional transforms which formed the east and west boundaries of the Seychelles microplate during breakup and early sea floor spreading. In some aspects, the conjugate margins are different from other volcanic margins; e.g. regional wedges of seaward dipping reflectors along the continent-ocean transition have not yet been reported. We ascribe this to the eruption of the most voluminous lavas during chron 29r, i.e on continental lithosphere in a late syn-rift setting. The enigmatic Laxmi Ridge is a complex marginal high comprised of both continental and oceanic crust. It was probably created during breakup, but may have experienced later magmatic and/or tectonic deformation.