Deep dynamics of subducting Indian slab revealed by mantle discontinuity structures beneath Hindu Kush from SdP observation

Despite numerous geophysical observations on Hindu Kush, fine structures of mantle discontinuities remain less explored. By stacking near-source SdP phases from large datasets, we conducted systematic imaging of mantle discontinuities beneath Hindu Kush. Compared with the IASP91 model, we find an abrupt topographic transition of the 410-km discontinuity (410) from uplifts of up to 41 km within the subducting slab to depressions of less than 20 km near the slab edge, as well as a slightly depressed 660-km discontinuity (660) with depths of 660-668 km, and a fluctuant 300-km discontinuity (300) with depths of 264-337 km. We suggest that the sinking Indian slab elevates the 410 due to its cold interior, and deepens it near the slab edge by the hot mantle upwelling of slab-entrained mantle escaping below the slab, but has almost no impacts on the 660. Moreover, the fluctuant 300 can be explained by the coesite to stishovite phase transition in the eclogite-rich mantle within the subduction zone. When considered alongside other studies, our seismic results offer new insights into subduction dynamics of the Indian slab.