Seismic investigations around an aseismic Comorin ridge, Indian Ocean

Abstract

Aseismic ridges and oceanic plateaux, typically buried under thick post-rift sediments, are isolated entities of enigmatic crustal character. Limited availability of deep seismic soundings hinders their precise characterization. Here, we present new crustal images from the Comorin ridge and adjoining basins in the Central Indian Ocean. Further, we seismically characterize the oldest oceanic crust south of Sri Lanka. We observe that the NW–SE-trending Comorin ridge, having distinct topography, is bounded by crustal blocks of contrasting ages and characters. Using seismic interpretation and potential field modelling, we propose its genesis as a transverse ridge with an anomalously thick ( c. 14 km) oceanic crust including considerable magmatic underplating. Additional constraints from plate reconstruction modelling suggest that a linear oceanic transform developed between India and Madagascar during their separation while the Marion hotspot remained in their close proximity. Based on several lines of evidence, we infer that shearing motion along the transform and coeval hotspot interactions are the likely emplacement mechanism for the ridge. The high-resolution seismic images demonstrate widespread crustal deformation in the form of high-angle faulting and long-wavelength folding. New findings have important implications for an improved understanding of the early Gondwana break-up, seafloor creation and subsequent compressional tectonics in the Indian Ocean. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.6073139