Magnetic structure of the uppermost mantle of the Eastern Continental Margin of India and Bay of Bengal inferred from Curie depths estimated by analysing shipborne magnetic data using Bayesian inversion�
Abstract
The Eastern Continental Margin of India (ECMI) is a classic passive margin formed during the Mesozoic breakup of the supercontinent Gondwanaland. Since its formation, the margin has undergone complex post-rift thermal subsidence, magmatic activity and interactions with adjacent tectonic plates. Extensive shipborne magnetic data have been acquired over the years, providing substantial coverage of the area. However, knowledge about the regional thermal structure and magnetic nature of the upper mantle of the ECMI and adjacent deep offshore Bay of Bengal is not understood uniformly throughout the region. In this study, we estimate Curie depth from shipborne magnetic data using a power spectrum inversion technique within a Bayesian framework, incorporating fractal source distribution and a priori sediment thickness to constrain the top depth of magnetic slab. The Curie depth is a proxy for the 580 �C isotherm, providing insight into the regional thermal structure and crustal rheology that controls post-rift thermal evolution and mantle magnetization. The obtained Curie depths range from 16 to 28 km with corresponding surface heat flow values varying between 55 and 85 mW m?�. A shallower Curie depth and higher heat flow are observed in northern part of the offshore Krishna�Godavari (KG) basin and the southern part of Mahanadi basin, linked to rift-related magmatic intrusions and mantle plume activity. Conversely, deeper Curie depths and lower heat flow characterize the Cauvery basin and the southern ECMI. Our results show, across much of the region from the Continent-Ocean Transition zone to deep offshore areas, the Curie depth lies below the Moho, suggesting that magnetic sources extend into the upper mantle. This suggests the presence of serpentinized upper mantle and exhumed mantle peridotite which provides the secondary magnetization. The obtained thermal lithosphere thickness varies from 50 to 90 km, shallower in the Krishna�Godavari and Mahanadi basins and deeper towards the Cauvery and central basins. Geotherms intersects mantle adiabat at 50 km depth in the KG and Mahanadi basins, signifying these are thermal overprint basins linked to magmatic activity. The obtained thermal lithosphere deepens from north to south, mirroring trends in the Lithosphere�Asthenosphere Boundary. Finally, a positive correlation between Curie depth and effective elastic thickness (Te) reflects the regional variation in crustal strength and tectono-magmatic processes controlling the margin evolution.
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