Conjugate nature of the Alleppey-Trivandrum Terrace Complex with the Northern Madagascar Ridge in the early opening model of the Arabian Sea: evaluation based on an integrated geophysical investigation

Abstract

The southwestern continental margin of India reveals the presence of an anomalous bathymetric high feature located in the mid-continental slope region off Trivandrum. Based on the analysis of the available geophysical data and plate tectonic reconstruction, this feature was interpreted as a scar of India-Madagascar separation, with its conjugate identified on the Northern Madagascar Ridge. Although the conjugate nature of the Alleppey-Trivandrum Terrace Complex and the Northern Madagascar Ridge was postulated, this inference has not yet been evaluated by comparing their geophysical signatures and crustal structure. The present study is aimed to derive and compare the crustal configuration of these two features using an up-to-date compilation of the bathymetry, gravity and magnetic data, and by employing integrated forward modelling of gravity and magnetic anomalies. Our derived crustal models for the Alleppey-Trivandrum Terrace Complex and the Northern Madagascar Ridge suggest that both these features can be explained in terms of thinned continental crust intermingled with volcanic intrusives. The crustal thicknesses of the Northern Madagascar Ridge and Alleppey-Trivandrum Terrace Complex at their conjugate continent-ocean boundaries are ~ 17�km and both these features are associated with high amplitude magnetic anomalies whose genesis is attributed to the volcanism caused by the Marion hotspot activity. Therefore, based on our integrated interpretation of the geophysical data, we support the earlier interpretation on conjugate nature of the Northern Madagascar Ridge and the Alleppey-Trivandrum Terrace Complex that was proposed based on the fitting of shape and size of the bathymetric notch observed in the southeastern continental margin of Madagascar with a bathymetric protrusion observed in the southwestern continental margin of India in the India-Madagascar pre-drift scenario. These features remained as a single unit prior to ~ 88�Ma and subsequently got separated during the India-Madagascar breakup.