Depth-Dependent Extension and Flexural response of Lithosphere to enormous sediment loading in the Bangladesh: Clues to uplift of Shillong Plateau

The Bangladesh is comprising up to 20 km of sedimentary deposits over the lithosphere and surrounded by India-Asia collision zone. Thus, deciphering the crustal architecture is essential for understanding the tectonic evolution. The sparse broadband seismic stations have provided estimates of Moho depth, however, the regional-scale variation in Moho topography remains poorly constrained. In this study, we performed a 3D gravity inversion constrained by seismically-derived Moho depth, to better delineate the crustal structure and thinning factor of the region. The inverted Moho depth beneath the Bangladesh varying from 22 – 32 km and exceed 32 km in the adjacent regions, while crustal thickness is less than 22 km in the Bengal Basin. The west-east lithospheric structure shows that the lithospheric thinning preceded crustal thinning in the northern Bangladesh, whereas in southern Bangladesh they occurred synchronously. Gravity modelling and stretching factors derived from tectonic subsidence support the presence of 5–8 km of magmatic underplating beneath the volcanic rifted margin in Bangladesh. 3D flexural backstripping analysis reveals that onshore Bengal Basin thermally subsided 5 – 7 km and adjacent region experienced a tectonic uplift < 2 km. The plume-related magmatism combined with prolonged sediment loading produced ~ 1 km of uplift of Shillong Plateau and remaining topography is generated by slip on the major thrust faults during the late Cenozoic shortening. Our findings highlight the key factors shaping the present-day crustal structure and topography of northeastern India.