MLR Key Laboratory of Earthprobe and Geodynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China.
Department of Earth Science and Engineering, Imperial College, London, SW7 2BP, UK.
Sci Rep. 2017 Jun 12;7(1):3243. doi: 10.1038/s41598-017-03578-z.
Using a topography-dependent tomographic scheme, the seismic velocity structure of the Eastern Tibetan Plateau, including the uplifted Longmenshan (LMS) orogenic belt, is accurately imaged in spite of the extreme topographic relief in the LMS region and thick sedimentary covers in the neighbouring Sichuan Basin. The obtained image shows a high-resolution upper crustal structure on a 500 km-long profile that is perpendicular to the LMS. The image clearly shows that the crystalline basement was uplifted within the LMS orogenic belt, and that the neighbouring Songpan-Ganzi Terrane was covered by a thick flysch belt, with evidence of near-surface thrust faults caused by convergence between Eastern Tibet and the Sichuan Basin. The indication that the lower crust beneath the LMS was folded and pushed upwards and the upper crust was removed by exhumation, supports the concept of a lower crustal channel flow beneath Eastern Tibet. The image also reveals that the destructive Wenchuan earthquake of year 2008 occurred in the upper crust, directly at the structural discontinuity between Eastern Tibet Plateau and the Sichuan Basin.
利用地形相关层析成像方案，尽管龙门山（LMS）造山带地区地形起伏极大且邻接的四川盆地沉积层较厚，仍精确地成像了青藏高原东部，包括隆升的龙门山造山带的地震速度结构。得到的图像显示了一条与 LMS 垂直的 500km 长剖面的高分辨率上部地壳结构。图像清楚地表明，结晶基底在 LMS 造山带内隆起，邻接的松潘-甘孜地块被厚厚的复理石带覆盖，存在由东西藏与四川盆地之间的汇聚引起的近地表逆冲断层的证据。LMS 下方的下地壳褶皱并向上推挤，上地壳被抬升出露的迹象，支持了东西藏下方存在下地壳流通道的概念。图像还揭示了 2008 年汶川地震发生在地表，就在青藏高原东部和四川盆地之间的构造不连续处。
