Upper mantle discontinuity structure beneath the Hindu Kush:Insights into dynamics of the Indian slab

Upper mantle discontinuities play an important role in slab dynamics and mantle responses in the subduction zones.Despite increasing numbers of seismological observations in the Hindu Kush, fine structures of mantle discontinuities still remain less explored, highlighting less understood interactions of the Indian slab and discontinuities. Here we collected a large dataset of several dense seismic networks/arrays, extracted near-source SdP waves in P-wave codas using the N-th root slant stackings, and then systematically imaged upper mantle discontinuities around the Indian slab beneath Hindu Kush. In comparison with the IASP91 model, we confirmed an abrupt topographic transition of the 410-km discontinuity(410) from uplifts of up to 41 km to depressions of less than 20 km near the slab edge and a slightly depressed 660-km discontinuity(660) with depths of 660 to 668 km below the slab front, as well as a fluctuating 300-km discontinuity(300) with depths of 264 to 337 km. We suggest that the 410 is elevated by the Indian slab due to the interior coldness, and deepened near the slab edge by the hot upwelling slab-entrained mantle that escapes below the slab bottom. Based on a depressed 410 inside the Indian slab and a 660with slight depressions below the slab, we infer that the subducted Indian slab currently stretches into the upper MTZ. Moreover,we interpret the fluctuant 300 as the coesite to stishovite phase transition in the subduction-zone mantle enriched in the eclogite.When considered alongside other studies, our results can provide more insights into the dynamics of the Indian slab and mantle responses.