Structure of lithospheric discontinuities beneath the southeast margin of Tibetan Plateau revealed by seismic daylight imaging and its dynamic significance

In order to further understand the dynamic problems such as tectonic evolution and deep seismogenic mechanism of the southeastern margin of the Tibetan Plateau, the structure of the lithospheric discontinuity was obtained by seismic daylight imaging based on teleseismic P-wave waveform data recorded by stations of China Seismological Science Array Exploration Project located in the region, and the accuracy and stability of the method were also discussed. The results show that the lithospheric thickness in the southeastern margin of the Tibetan Plateau is thinner in the west and thicker in the east. The thinnest lithospheric thickness near Tengchong volcano in Yunnan-Myanmar-Thailand block is about 60 km. The thinner lithosphere may be caused by the upwelling of asthenosphere mantle material. The lithospheric thickness of the Yangtze block is gradually thinning from Sichuan basin to the south, especially the thickest beneath the Sichuan basin, whose lithospheric thickness can reach about 190 km. Meanwhile, obvious discontinuities have been detected at a depth of about 150 km beneath Tengchong volcano, which may be the original magma source of volcano. The continuity of the structure of the Indo-China block and the Yunnan-Myanmar-Thailand block further provides seismological evidence for the eastward spillover of low-velocity materials from Tengchong volcano caused by the pushing of the Indian Plate. The northernmost section of the studied area shows that there are obvious local high-velocity variations in the depth range of 50−250 km within the Emeishan Large Igneous Province and the crust above it. The uneven distribution characteristics may be related to the magma bottom intrusion during the Permian volcanic eruption and the multiple tectonic activities since the Mesozoic and Cenozoic.