华北克拉通中部过渡带SKS波分裂研究:鄂尔多斯东南角的局部软流圈绕流

本文对布设在华北克拉通东西两块体交界区域的宽频带流动地震观测台阵和部分固定台站的远震波形记录开展了SKS波分裂研究.结果显示,鄂尔多斯块体内部的各向异性比较弱,剪切波分裂导致的时间延迟一般小于0.7s.鄂尔多斯块体东缘的山西断陷带和太行山以及华北平原西部均表现出了比较强的各向异性,时间延迟大于1.0s.特别是在太行山地区观测到的ENE趋向的快波偏振方向明显不同于鄂尔多斯块体和华北平原地区的近E-W和ESE方向的快波偏振方向.在华北克拉通东西两块体交界过渡带的太行山地区观测到的显著上地幔各向异性及变化可能对应于围绕鄂尔多斯块体东南角的局部软流圈绕流,而后者可能起因于鄂尔多斯块体的逆时针旋转以及青藏高原软流圈沿秦岭大别造山带向东的流动.

SKS wave splitting study of the transition zone at the central portion of the North China Craton

SKS wave splitting analysis is performed to image the upper mantle anisotropy on the teleseismic data recorded by Peking University temporary seismic arrays and several permanent seismic stations in the transition zone at the central portion of the North China Craton(NCC). Weak seismic anisotropy is observed inside the Ordos block with delay times less than 0.7 s. The delay times in the eastern margin of the Ordos block, including the Shanxi Basin, Taihang mountain and the North China plain are larger than 1.0 s, showing strong anisotropy in the upper mantle. The ENE fast polarization directions in the Taihang mountain are significantly different from the E-W to ESE fast polarization directions in the Ordos block and the North China plain to the west and east. As the transition zone of the eastern and western NCC, the variation of the upper mantle anisotropy in the Taihang mountain may reveal a local asthenospheric flow around the southeastern corner of the Ordos block, induced by the anticlockwise rotation of the Ordos block and the eastward asthenospheric flow along the Qinling-Dabie orogen from the northeastern Tibetan Plateau.