Sediment and Crustal Structure along 85oE and Ninetyeast Ridges in the Bay of Bengal: Geodynamic Implications

Abstract:

The Bay of Bengal (BOB) region is characterized by the presence of two linear N-S trending aseismic ridges, the 85°E and Ninetyeast ridges which have progressively buried below thick sediments towards north. We present here the results of an integrated interpretation of geophysical data using multichannel seismic reflection, gravity and magnetic datasets over these two ridges to study the crustal structure and mode of their emplacement. The ridges divide the deep sedimentary BOB region into three major sub-basins. Considering the sediment deposition pattern within the sub-basins and over the ridges, it is found that both ridge structures have played a role in sediment dispersal pattern during the pre- and post Bengal Fan sedimentation. The Geoid-Topography Ratio (GTR) analysis indicates that both the ridges are compensated at shallow depths. Seismically constrained gravity and magnetic models and flexural gravity modeling over these ridges support their volcanic origin, and suggest the following: i) 85°E Ridge was emplaced in off-ridge environment (Te=10-15 km); ii) the higher Te values of ~ 25 km over the Afanasy Nikitin Seamount (ANS) reflect the secondary emplacement of the seamount peaks in off-ridge environment, iii) that the emplacement of the Ninetyeast Ridge north of 2°N occurred in an off-ridge environment as indicated by higher Te values (25-30 km). These results attain significance in terms of understanding of the interactions between plume- volcanism and lithosphere in the Bay of Bengal.