Isostatic response of the Laccadive Ridge from admittance analysis of gravity and bathymetry data
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The Laccadive Ridge (L-R), trending roughly parallel to the west coast of India, is an intriguing segmentof the northernmost Chagos-Laccadive Ridge (C-L-R) system. Although crustal nature and isostatic response of the southern C-L-R iswell known, there are no similar studies on the L-R. In the present study, the isostatic response of the lithosphere beneath the L-R is estimated so as to characterize its crustal nature, total crustal as well as effective elastic plate thickness and mode of compensation. Twelve gravity and bathymetry profiles across the ridge were analyzed using linear transfer function and forward model techniques. The observed admittance function within the diagnostic waveband of 250 less than lambda greater than 80 km (0.025 less than k greater than 0.080 km sup(-1)) fits well with (1) the Airy model whose average crustal thickness (Tc) and density are 17 plus or minus 2 km and 2.7 + 10 sup(3) kg m sup(-3), respectively, and (2) the thin plate flexure model of isostasy with an effective elastic plate thickness (Te) of 2-3 km. The estimated average crustal thickness and density are in good agreement with published seismic refraction results over the ridge. The results of the present study support an Airy model of isostasy for the L-R. The low Te value, in view of other published results in the study area, suggests stretched and loaded continental lithosphere of the L-R during the evolution of the western continental margin of India.
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