Crustal architecture and isostatic compensation of the Comorin Ridge, central Indian Ocean: Implications for the breakup of east Gondwana

Abstract

The Comorin Ridge, located off the southwest margin of Sri Lanka is an important geological feature with significant relevance to understand the breakup of eastern Gondwanaland. Earlier geophysical studies over this ridge provided several contrasting views due to which its origin and nature of emplacement could not be established very well. In this study, an integrated interpretation of bathymetry, gravity, geoid, and ship-borne magnetic data is carried out to bring out a well-constrained evolution model for the ridge. Results of 3-D gravity inversion of Crustal Bouguer anomalies and joint gravity-magnetic modeling indicate that the southern part of the ridge is underlain by 7–12 km thick crust intruded with volcanic rocks and the presence of 13–18 km of anomalously thicker crust below the northern part of the ridge. Further, crustal models, spatial variations in Geoid-Topography Ratio (GTR), and the effective elastic thickness (Te) value obtained in this study suggest a two-stage emplacement model for the evolution of the ridge. The observed lower Te values (7–8 km) in the southern part (0.5°N–3.5°N) and its proximity to the C34ny spreading anomaly suggest its emplacement on the oceanic lithosphere due to Marion plume activity along a fracture zone during ~88–84 Ma. On the other hand, relatively higher Te values (12.5–15 km) in the northern part (3.5°N–6.5°N) with absence seafloor-spreading magnetic anomalies suggests that it could be a marginal basement high formed at the continent-ocean boundary (COB) during the second phase of rifting between India and Sri Lanka (~94 Ma).