Analyses of multichannel seismic reflection, gravity and magnetic data along a regional profile across the central-western continental margin of India

Abstract

Analyses of multichannel seismic reflection, gravity, magnetic and bathymetry data along a regional profile across the central-western continental margin of India have revealed the depositional pattern of sediments, crustal structure and tectonics. The four most distinct and varied crustal regions of the margin are palaeo-shelf edges, shelf margin basin, Prathap and Laccadive Ridges and the Arabian Basin. The shelf margin basin is carpeted by ∼4.5 km maximum thick aggraded and prograded Paleocene to Holocene sediments. Six major seismic sequences of the sediments of the margin are identified and their ages are assigned on correlation with drill-well results. Development of the sequence boundaries is attributed to the events of rifting of western India, eustatic sea-level changes, Indian and Eurasian plate collision and Himalayan orogeny. Tilted fault blocks (half-grabens) located almost equi-distance from the igneous construct of the ‘Prathap Ridge’ in the shelf margin basin suggest a failed rift associated with stretched continental crust of the basin. 2-D model studies of gravity and magnetic anomalies, constrained by the seismic results, have revealed 6 to 27 km thick crust across the margin. The Laccadive Ridge crust limited by two volcanic intrusives and a steep scarp at its western end is ∼16 km thick. It gradually thins towards offshore and juxtaposed with early Tertiary normal oceanic crust ∼6 km thick of the Arabian Basin. The crustal thickness and velocity and density structure of the ridge are comparable to that of the Laxmi Ridge, a continental sliver. The inferences and abrupt change in magnetic and gravity anomaly signatures across the western end of the Laccadive Ridge mark the zone of transition from continental to oceanic crust.