Plume-ridge interactions in the Central Indian Ocean Basin: Insights from new wide-angle seismic and potential field modelling

Abstract

The central Indian Ocean Basin (CIOB) comprises numerous tectonic elements related to the early-mid Cretaceous Antarctica-India rifting and subsequent formation of the Indian Ocean. A protracted rift-drift journey of the Indian plate was accompanied with frequent interactions between concurrent mantle plumes and spreading centres. In 2015, we acquired ~420-km long wide-angle reflection and refraction seismic profile in the CIOB south off Sri Lanka, which lies in close proximity to the Indian Ocean Geoid Low. Our primary aim is to decipher crustal and uppermost mantle structure variations with an emphasis on prior tectonics. Two dimensional travel-time tomographic inversion complemented by potential field modelling yields sub-surface velocity-interface structures of the CIOB. Results demonstrate presence of an anomalously thick crust (~14 km) underneath the Comorin ridge, which gradually thins out in the east towards the centre of the geoidal low. We observe distinct evidence for an anomolously high velocity lower crust (velocities greater than 7 km/s across a ~ 160 km wide region) west of 790 E longitude. However, crust to the east of this point appears to be normal oceanic type. We attribute the lateral diversity in the crustal type to possible magmatic underplating beneath the Comorin ridge. We interpret that the concurrent plume-ridge interaction during the late Cretaceous India-Madagascar break-up may have caused this crustal underplating. These findings have significant implications towards better understanding of plume-ridge interaction processes along various passive margins as well as precise reconstruction of India-Madagascar dispersal.