Antigorite-induced seismic anisotropy and implications for deformation in subduction zones and the Tibetan Plateau
Antigorite-induced seismic anisotropy and implications for deformation in subduction zones and the Tibetan Plateau
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DOI：
10.1002/2013jb010661
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发表时间：
2014-03
影响因子：
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通讯作者：
T. Shao;S. Ji;Y. Kondo;K. Michibayashi;Qian Wang;Zhiqin Xu;Shengsi Sun;D. Marcotte;M. Salisbury
中科院分区：
文献类型：
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作者：
T. Shao;S. Ji;Y. Kondo;K. Michibayashi;Qian Wang;Zhiqin Xu;Shengsi Sun;D. Marcotte;M. Salisbury
本研究是Ji et al. （2013a）在《地球物理研究杂志》（Journal of Geophysical Research）上发表的论文的后续，为反长花岗岩蛇纹岩的地震和结构特性提供了一种新的校准方法。将高压下测得的反长花岗岩蛇纹岩的实验室速度与使用电子背散射衍射技术测得的晶体学优选定向数据进行比较，表明高T蛇纹岩的地震各向异性（基本上由反长花岗岩c轴结构控制）与操作滑动系统无关，但强烈依赖于岩石所经历的有限应变的状态和大小。对压力和温度下的实验数据进行外推表明，无论是在冷俯冲带还是热俯冲带，Vp各向异性都随着压力的增加而减小，而横波分裂（ΔVs）和Vp/Vs都随着压力的增加而增大。对于一个寒冷的、陡峭俯冲的板块，反长花岗岩最有可能通过近同轴的平坦或海沟平行运动而变形，形成海沟平行的地震各向异性。然而，对于一个热的、浅俯冲的板块，反长岩很可能是由简单的剪切或挤压变形的。当俯冲倾角小于30°时，可以观察到槽-正向地震各向异性。
The present study, which is a follow-up of the Journal of Geophysical Research paper by Ji et al. (2013a), provides a new calibration for both seismic and fabric properties of antigorite serpentinites. Comparisons of the laboratory velocities of antigorite serpentinites measured at high pressures with crystallographic-preferred orientation data measured using electron backscatter diffraction techniques demonstrate that seismic anisotropy in high T serpentinite, which is essentially controlled by the antigorite c axis fabric, is independent on the operating slip system but strongly dependent on the regime and magnitude of finite strain experienced by the rock. Extrapolation of the experimental data with both pressure and temperature suggests that Vp anisotropy decreases but shear wave splitting (ΔVs) and Vp/Vs increase with increasing pressure in either cold or hot subduction zones. For a cold, steeply subducting slab, antigorite is most likely deformed by nearly coaxial flattening or trench-parallel movements, forming trench-parallel seismic anisotropy. For a hot, shallowly subducting slab, however, antigorite is most likely deformed by simple shear or transpression. Trench-normal seismic anisotropy can be observed when the subducting dip angle is smaller than 30°. The geophysical characteristics of the Tibetan Plateau such as strong heterogeneity in Vp, Vs and attenuation, shear wave splitting and electric conductivity may be explained by the presence of strongly deformed serpentinites in lithospheric shear zones reactivated along former suture zones between amalgamated blocks, hydrated zones of subducting lithospheric mantle, and the crust-mantle boundary if the temperature is below 700°C in the region of interest.