Subduction of the Indian lithosphere beneath the Tibetan Plateau and Burma

Subduction of the Indian lithosphere under Eurasia plays an important role in the tectonic evolution of the Tibetan plateau and surrounding regions. To improve our knowledge of pertinent mantle structures through tomographic imaging we combine P-wave arrival time data from temporary arrays in Tibet and stations of the Chinese Seismograph Network with reprocessed data from the International Seismological Centre. The new images reveal considerable spatial variations in mantle structure along the collision zone, and the horizontal distance over which presumed (continental) Indian lithosphere slides northward beneath the plateau decreases from west (where it underlies the Himalayas and the entire plateau) to east (where no indication is found for present-day underthrusting beyond the Himalayan Block and Indus–Tsangpo suture). P-wavespeed appears low in the shallow mantle beneath much of central and eastern Tibet. These observations suggest that Indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of Asian origin. The (continental) parts of the Indian plate that currently underthrust or subduct below the plateau appear generally detached from the (oceanic) slab fragments that subducted longer ago and that have been detected deeper in the mantle, except perhaps in the central part of the collision zone (80–90°E). This suggests that ongoing India–Eurasia collision must increasingly be driven by other forces, such as subduction of the Indian plate further west and east (e.g. beneath Indochina). Our images reveal structures associated with eastward subduction along the Burmese arc southeast of the eastern Himalayan syntaxis. The Tengchong volcanic complex in southwest China is marked by slow wave propagation to ~ 150 km depth, suggesting a causal link to subduction along the Burmese arc; the low velocities beneath the Red River fault region extend to greater depth and may be related to upper mantle processes further southeast.