The upper crustal anisotropy of Yunnan area, SE margin of Tibetan Plateau, is investigated by measuring the shear wave splitting of local earthquakes. The mean value of the measured delay times is 0.054 s and far less...The upper crustal anisotropy of Yunnan area, SE margin of Tibetan Plateau, is investigated by measuring the shear wave splitting of local earthquakes. The mean value of the measured delay times is 0.054 s and far less than that from Pms splitting analysis, indicating that the crustal anisotropy is contributed mostly from mid-lower crust. The fast polarization directions are mostly sub-parallel to the maximum horizontal compression directions while the stations near fault zones show fault-parallel fast polarization directions, suggesting both stress and geological structure contribute to the upper crust anisotropy.Comparing fast polarization directions from shear wave splitting of local earthquakes and Pms, large angle differences are shown at most stations, implying different anisotropy properties between upper and mid-lower crust. However, in southwestern Yunnan, the fast polarization directions of Pms and Swave splitting are nearly parallel, and the stress and surface strain rate directions show strong correlation, which may indicate that the surface and deep crust deformations can be explained by the same mechanism and the surface deformation can represent the deformation of the whole crust. Therefore,the high correlation between surface strain and mantle deformation in this area suggests the mechanical coupling between crust and mantle in southwestern Yunnan. In the rest region of Yunnan, the crustmantle coupling mechanisms are supported by the lack of significant crustal anisotropy with Ne S fast polarization directions from Pms splitting. Therefore, we conclude that the crust and upper mantle are coupled in Yunnan, SE margin of Tibetan Plateau.展开更多
Usual ductile shear zone has relatively high strain magnitude. However,for high-grade metamorphic rocks in Daqingshan area,the related strain is very low with weakly developed lineation. Significantly,the finite strai...Usual ductile shear zone has relatively high strain magnitude. However,for high-grade metamorphic rocks in Daqingshan area,the related strain is very low with weakly developed lineation. Significantly,the finite strain type with a K-value slightly lower than 1 and is characterized by compressional strain. Because the special tectonic environment with high temperature,the percentage of melt is relatively higher,which leads to a series of microscopic phenomenon such as multi-grain quartz bands,feldspar three edges equilibrium-like texture,granular flow,etc. As a consequence,the tectonites in the studied area illustrate a unique character: obvious rheological meso-deformation structure but with very weak intracrystalline micro-deformation.展开更多
基金supported by the National 973 Project of China (No.2013CB733303)the open fund of Key Laboratory of Geospace Environment and Geodesy,Ministry of Education (No.15-02-07)
文摘The upper crustal anisotropy of Yunnan area, SE margin of Tibetan Plateau, is investigated by measuring the shear wave splitting of local earthquakes. The mean value of the measured delay times is 0.054 s and far less than that from Pms splitting analysis, indicating that the crustal anisotropy is contributed mostly from mid-lower crust. The fast polarization directions are mostly sub-parallel to the maximum horizontal compression directions while the stations near fault zones show fault-parallel fast polarization directions, suggesting both stress and geological structure contribute to the upper crust anisotropy.Comparing fast polarization directions from shear wave splitting of local earthquakes and Pms, large angle differences are shown at most stations, implying different anisotropy properties between upper and mid-lower crust. However, in southwestern Yunnan, the fast polarization directions of Pms and Swave splitting are nearly parallel, and the stress and surface strain rate directions show strong correlation, which may indicate that the surface and deep crust deformations can be explained by the same mechanism and the surface deformation can represent the deformation of the whole crust. Therefore,the high correlation between surface strain and mantle deformation in this area suggests the mechanical coupling between crust and mantle in southwestern Yunnan. In the rest region of Yunnan, the crustmantle coupling mechanisms are supported by the lack of significant crustal anisotropy with Ne S fast polarization directions from Pms splitting. Therefore, we conclude that the crust and upper mantle are coupled in Yunnan, SE margin of Tibetan Plateau.
基金Supported by Project of National Natural Science Foundation of China(Nos.41230206,41340032)
文摘Usual ductile shear zone has relatively high strain magnitude. However,for high-grade metamorphic rocks in Daqingshan area,the related strain is very low with weakly developed lineation. Significantly,the finite strain type with a K-value slightly lower than 1 and is characterized by compressional strain. Because the special tectonic environment with high temperature,the percentage of melt is relatively higher,which leads to a series of microscopic phenomenon such as multi-grain quartz bands,feldspar three edges equilibrium-like texture,granular flow,etc. As a consequence,the tectonites in the studied area illustrate a unique character: obvious rheological meso-deformation structure but with very weak intracrystalline micro-deformation.
