Tectonic framework of Laccadive Ridge in Western Continental Margin of India

Abstract

From the analysis of the satellite derived high resolution free air gravity data it is inferred that the evolutionary history of the Western Continental Margin of India to north and south of Goa appears to be totally different . The shelf edge is continuous and not disturbed in the northern part whereas to the south (south of 16°N) it has been affected by the onshore tectonics. It is hotly debated if the Laccadive Ridge (northern part of the Chagos-Laccadive Ridge) is continental or oceanic in nature or just of volcanic origin. From the filtered maps of the free air gravity anomalies, sources at different depths can be deciphered that help build an evolutionary model of the much debated Laccadive Ridge. The low pass filtered maps depicting deeper features, show a persistence of NW–SE to NS Dharwarian trends and it appears that the Laccadive Ridge to the north of around 8.5°N is of continental origin being bounded to the south and north by the offshore extension of the Bhavani Shear and Chapporo lineament respectively. It may have separated from India along with Madagascar during Cretaceous. At the Cretaceous Tertiary boundary as Laccadive-India passed over the Reunion hotspot, the pre-existing faults on the Laccadive Ridge were re-activated and the hotspot trace was left behind in the intermediate/shallow wavelength of the anomalies, as intrusives in the Laccadive Ridge. These are reflected in the High Pass filtered maps, depicting shallow to intermediate wavelength anomalies, which show NE–SW structures. The crustal structure derived from the 2D model of the satellite derived free air gravity data and a representative gravity-magnetic profile from ship borne data also depict continental nature of the Laccadive Ridge with emplacement of volcanic intrusives as it passed over the Reunion hotspot.