THE BOUNDARIES BETWEEN THE TIBETAN PLATEAU AND THE INDIAN AND EURASIAN PLATES OBSERVED WITH SEISMIC RECEIVER FUNCTIONS

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by mapping the deep seismic discontinuities like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of these discontinuities with the P and S receiver function techniques beneath the southern, northern and eastern boundaries of Tibet along several profiles with emphasis on LAB observations. The LAB of the Indian and Asian plates is well imagedwith S receiver functions. The subducting Indian lithosphere reaches as far north as central Tibet. There is no subduction in the north-west of Tibet at the boundary to the Tarim basin and also not in eastern Tibet at the boundary to the Sichuan basin. Remarkably, the Tibetan lithosphere is thickening at the boundary to the Tarim basin and thinning at the boundary of the Sichuan basin. The reason is unclear; there might be delamination of parts of the mantle lithosphere beneath eastern Tibet. The Moho is also clearly observed in P and S receiver functions. The Indian Moho is smoothly deepening below Tibet whereas the Moho is step like deepening towards Tibet at the northern and eastern boundaries. Signals from the two global discontinuities at 410 and 660 km depth are delayed in northern Tibet which indicates a slower upper mantle there.

کلیدواژه ها:

Tibetan plateau ، Seismic receiver functions ، Lithosphere-asthenosphere boundary