Abstract: The formation of passive rifted margins is a complex process; involves the deformation of pre-existing lithosphere whose rheological properties are the product of numerous earlier tectonic events. In the present study, the Eastern Continental Margin of India (ECMI) and Bangladesh Margin architecture were examined to deduce the margin architecture, ocean-continent transition (OCT) and their structural evolution. Linking deep seismic profiles with regional-scale gravity inversion and 2-D gravity forward modelling illuminated basement configuration, crustal thickness and Moho topography, thereby revealing the modes of rift evolution and the location of the Continent-Ocean Boundary (COB) along these margins. The basement, particularly in shelf and slope regions of eastern peninsular India, is traversed by nearly coast perpendicular grabens, and their seaward continuity is delineated up to 125 km from the coastline. Three different types of continental margin are present along the ECMI, 1) sheared rift on the southern segment of the ECMI, up to 14°N latitude (offshore the Southern Granulite Terrain), 2) hyper-extended rift in the central segment between 14°N and 17°N (offshore the Dharwar Craton), and 3) hypo-extended rift on the northern segment between 17°N and 20°N (offshore the Eastern Ghats Mobile Belt). Lateral variation of crustal rheology from India hinterland with rift segmentation reveal striking spatial heterogeneities that separate three distinct corridors along the ECMI. The graben terminations, crustal thickness, and Moho topography of both the ECMI and offshore Bengal Basin clearly suggest that the COB runs nearly parallel to the coastline of peninsular India, but takes an orthogonal turn offshore the Bengal Basin and connects the palaeo-continental shelf and the Rajmahal-Sylhet Line in the onshore Bengal Basin. The absence of rifted crustal blocks on the Bangladesh margin and the continuity of the COB into the onshore Bengal Basin together imply that the present Bangladesh region was under marine conditions at least until the beginning of Bengal Fan sedimentation.

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