华南块体各向异性分区及上地幔动力学含义

Anisotropic Zoning and Dynamic Mechanism of Upper Mantle beneath South China Block

利用SKS波分裂方法,对布设在华南地区的宽频带流动地震观测台阵数据进行分析。研究结果表明,华南块体(SCB)的SKS波分裂自西向东存在明显的变化。在华南块体西部克拉通岩石圈保留完整的四川盆地区域,SKS波分裂不明显,反映该区域岩石圈厚且缺乏大规模的一致性变形;在四川盆地东缘褶皱带区域,SKS波分裂快波方向主要为NNE向,分裂延迟时间可以达到1 s左右,记录了该区域岩石圈地幔经历的一致的显著变形;华南块体东部的SKS波分裂快波方向主要为ENE向,分裂延迟时间为1 s左右,该区域各向异性主要来自软流圈流动的贡献,与大地幔楔的流动方向契合;四川盆地东缘以东200 km范围内,各向异性结果大部分显示为Null值,显示该区域在地质历史上可能发生过复杂的地球动力学过程。

Analyzing the broadband portable seismic stations deployed in South China Block(SCB),the SKS wave splitting method is used to study the anisotropy of the upper mantle beneath the region.The results show that the SKS wave splitting parameters in SCB vary significantly from west to east.In Sichuan Basin(SB)where the cratonic lithosphere remains relatively intact,splits of SKS wave are not obvious,reflecting that the lithosphere here is thick and undeformed.In the fold belt system at the eastern margin of the SB,fast polarization directions of the SKS wave splitting are mostly in NNE direction with about 1 s splitting delay times,indicating that the thick lithosphere has undergone deformation and the anisotropy owing to the deformation has been frozen in the lithosphere.In the eastern part of the SCB,the fast polarization directions are mainly ENE and splitting delay times are about 1 s.The anisotropy in this area mainly attributes to flow of the asthenosphere coinciding with the mantle-wedge flow.Finally,many Null splitting results are observed in the transition zone of the eastern margin of the SB with 200 km width,which may be caused by the complicated geological tectonic events it has been suffered.