Characteristics of the lithosphere physical structure in eastern margin of the Qinghai-Tibet plateau and their deep tectonic implications

The eastern margin of Qinghai-Tibet Plateau is the key area where crustal material of the plateau is squeezed out to the east. In order to explore the crust and mantle structural responses to the squeezing-out process and its deep geological evidences, satellite altimetry gravity, seismic data from 634 digital seismological network stations of the Himalaya project (phase one), and the two long-period magnetotelluric sounding data across Longmen Shan and Panxi tectonic belts are used in this study to obtain apparent density, P-wave velocity anomaly and the electrical property of the eastern margin of the plateau. Physical property imaging shows that: (1) Middle-lower crust and upper mantle of the Songpan and Sichuan-Yunnan blocks present low density, low-velocity, high conductivity, and more ductile characteristics. In some area, the ductile material could reach 150 km depth; (2) The Yangtze craton lithosphere beneath the Sichuan Basin has a stable high-density, high-speed and high-resistance rigid structure, which could extends downward as deep as 150 km; (3) Lateral and vertical heterogeneity of physical properties of the eastern margin of the plateau provides material and tectonic basis to reveal the uplift mechanism for the Longmen Mountains tectonic belt and the Sichuan-Yunnan block; (4) Lithosphere physical structure along the Minshan-Longmen-Jinping-Jade Dragon Snow Mountain tectonic belt presents distinct density and velocity gradients, which probably represent the location of western boundary of the middle-upper Yangtze block.