摘要
青藏高原东缘是研究青藏高原地壳物质向东侧向挤出的焦点地区.为探索青藏高原东向挤出其东部壳幔结构响应及深部地质构造依据,本文利用卫星测高重力数据、数字地震台网("喜马拉雅"项目一期)634个台站的观测数据、以及跨越龙门山构造带、攀西构造带的两条长周期大地电磁测深资料,获得了青藏高原东缘视密度物性结构、P波速度异常结构、以及电性成像结构.物性成像结果表明:(1)松潘地块、川滇地块中-下地壳、上地幔具有低密度、低速、高导的韧性物性结构,部分地区这种韧性物性结构甚至可到达150 km处;(2)四川盆地下方扬子克拉通岩石圈具有稳定的高密度、高速、高阻的刚硬物性结构,其结构向下可延伸至150 km深处;(3)青藏高原东缘横向和垂向的物性结构差异,为揭示龙门山构造带、川滇地块隆升机制提供了物质基础和动力学依据;(4)岩石圈物性结构中,沿岷山一龙门山一锦屏山一玉龙雪山构造带一线存在明显的密度、速度梯级带,其东西两侧呈明显物性二元结构,该物性梯级带可能反映了中上扬子地块西边界位置.
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.