Abstract:

There are a lot of Cenozoic potassic and ultrapotassic lavas in the northern Qinghai-Tibet Plateau, their existing is an enigma.We have collected all the available arrival time data recorded by the temporary seismic stations and phase reports from the International Seismological Center in Tibet and its surrounding areas.In the tomographic inversion, we have used 139,021 P-wave arrival times from 9,649 teleseismic events recorded by 305 seismic stations.Tomographic images show that the frontier of the lithospheric mantle of Indian plate （ILM） subducted beneath the center of Qiangtang terrane, and there is a great scale vertical low-velocity zone from deep to surface at the frontier of ILM.It supplies a channel for deep mantle upwelling.Hot materials of deep asthenospheric mantle might flow upward along the channel，then potassic and ultrapotassic lavas erupted in the northern Tibet.Cenozoic potassic and ultrapotassic lavas in the north Tibet are the direct result of northward subducting of ILM.

Key words: volcanic zone in the northern Qinghai-Tibet Plateau, low-velocity plume, Indian lithospheric mantle, tomography