Does the Laxmi Ridge continue towards the Laccadive Ridge? New insights from an integrated geophysical study

Abstract

The Laxmi and Laccadive ridges are two major aseismic ridges in the NW Indian Ocean. Bathymetry, gravity and magnetic data and their derivatives are analyzed and modelled to assess the interrelationship between both the ridges as well as to establish their crustal structure, nature and isostatic compensation. Boundaries of the Laxmi and Laccadive ridges are delineated by tilt derivative with constraints from available seismic-sections. Integrated gravity and magnetic models reveal that both the ridges have almost similar crustal layers and are underplated all along its length. Crustal models also depict that both the ridges are carpeted with flood basalt and heavily intruded. 3D coherence between Mantle Bouguer Anomaly and residual bathymetry reveals that the elastic plate thickness and subsurface to surface load ratio for both the ridges vary from 3 to 4 km and 0.7 to 0.8, respectively. Several characteristic similarities viz. crustal structure and nature, elastic plate thickness, magmatism have been observed for both the ridges. Seismic sections near the junction of the ridges suggest that the basement high corresponding to the Laxmi Ridge is further continued towards the Laccadive Ridge. In addition, the northwestern part of the Laccadive Ridge has NW-SE structural lineaments similar to that of the NW-SE segment of the Laxmi Ridge. Based on results of the present and previous studies, we infer that (i) the Laxmi Ridge is extended southeastward towards the Laccadive Ridge, (ii) both the ridges are continental slivers which are underplated as well as intruded and carpeted by volcanics, and (iii) both the ridges are locally compensated.