Legendre Cédric P, Deschamps Frédéric, Zhao Li, Chen Qi-Fu
Institute of Earth Sciences, Academia Sinica, 128 Academia Road, Sec. 2, Nangang, Taipei 11529, Taiwan.
Present address: Department of Geosciences, National Taiwan University, No. 1, Sec 4, Roosevelt Rd., Taipei 10617, Taiwan.
Sci Rep. 2015 Nov 9;5:16644. doi: 10.1038/srep16644.
The Tibetan Plateau results from the collision of the Indian and Eurasian Plates during the Cenozoic, which produced at least 2,000 km of convergence. Its tectonics is dominated by an eastward extrusion of crustal material that has been explained by models implying either a mechanical decoupling between the crust and the lithosphere, or lithospheric deformation. Discriminating between these end-member models requires constraints on crustal and lithospheric mantle deformations. Distribution of seismic anisotropy may be inferred from the mapping of azimuthal anisotropy of surface waves. Here, we use data from the CNSN to map Rayleigh-wave azimuthal anisotropy in the crust and lithospheric mantle beneath eastern Tibet. Beneath Tibet, the anisotropic patterns at periods sampling the crust support an eastward flow up to 100°E in longitude, and a southward bend between 100°E and 104°E. At longer periods, sampling the lithospheric mantle, the anisotropic structures are consistent with the absolute plate motion. By contrast, in the Sino-Korean and Yangtze cratons, the direction of fast propagation remains unchanged throughout the period range sampling the crust and lithospheric mantle. These observations suggest that the crust and lithospheric mantle are mechanically decoupled beneath eastern Tibet, and coupled beneath the Sino-Korean and Yangtze cratons.
青藏高原是新生代印度板块与欧亚板块碰撞的结果，碰撞产生了至少2000千米的汇聚。其构造主要由地壳物质向东挤出所主导，对此已有模型解释，这些模型要么暗示地壳与岩石圈之间存在力学解耦，要么暗示岩石圈变形。区分这些端元模型需要对地壳和岩石圈地幔变形进行约束。地震各向异性的分布可通过面波方位各向异性的测绘来推断。在此，我们利用中国国家数字地震台网（CNSN）的数据，绘制了青藏高原东部地壳和岩石圈地幔中瑞利波方位各向异性图。在青藏高原之下，在对地壳进行采样的周期内，各向异性模式表明存在向东的流动，一直到东经100°，并在东经100°至104°之间向南弯曲。在更长的周期内，对岩石圈地幔进行采样时，各向异性结构与绝对板块运动一致。相比之下，在中朝克拉通和扬子克拉通中，快速传播方向在对地壳和岩石圈地幔进行采样的整个周期范围内保持不变。这些观测结果表明，青藏高原东部下方的地壳和岩石圈地幔在力学上是解耦的，而在中朝克拉通和扬子克拉通下方是耦合的。
