Shear wave velocity structure of the crust and upper mantle in Southeastern Tibet and its geodynamic implications  

作　　者：Zhiqi ZHANG Huajian YAO Yan YANG 

机构地区：[1]Laboratory of Seismology and Physics of Earth’s Interior,School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China [2]Mengcheng National Geophysical Observatory,University of Science and Technology of China,Mengcheng 233500,China [3]CAS Center for Excellence in Comparative Planetology USTC,Hefei 230026,China

出　　处：《Science China Earth Sciences》2020年第9期1278-1293,共16页中国科学（地球科学英文版）

基　　金：supported by Key Research and Development Project of the Ministry of Science and Technology(Grant No.2018YFC1503400);China Earthquake Science Experiment Project,China Earthquake Administration(Grant No.2018CSES0101)。

摘　　要：Southeastern Tibet,which has complex topography and strong tectonic activity,is an important area for studying the subsurface deformation of the Tibetan Plateau.Through the two-station method on 10-year teleseismic Rayleigh wave data from 132 permanent stations in the southeastern Tibetan Plateau,which incorporates ambient noise data,we obtain the interstation phase velocity dispersion data in the period range of 5–150s.Then,we invert for the shear wave velocity of the crust and upper mantle through the direct 3-D inversion method.We find two low-velocity belts in the mid-lower crust.One belt is mainly in the SongPan-GangZi block and northwestern part of the Chuan-Dian diamond block,whereas the other belt is mainly in the Xiaojiang fault zone and its eastern part,the Yunnan-Guizhou Plateau.The low-velocity belt in the Xiaojiang fault zone is likely caused by plastic deformation or partial melting of felsic rocks due to crustal thickening.Moreover,the significant positive radial anisotropy(VSH>VSV)around the Xiaojiang fault zone further enhances the amplitude of low velocity anomaly in our VSVmodel.This crustal low-velocity zone also extends southward across the Red River fault and farther to northern Vietnam,which may be closely related to heat sources in the upper mantle.The two low-velocity belts are separated by a high-velocity zone near the Anninghe-Zemuhe fault system,which is exactly in the inner and intermediate zones of the Emeishan large igneous province(ELIP).We find an obvious high-velocity body situated in the crust of the inner zone of the ELIP,which may represent maficultramafic material that remained in the crust when the ELIP formed.In the upper mantle,there is a large-scale low-velocity anomaly in the Indochina and South China blocks south of the Red River fault.The low-velocity anomaly gradually extends northward along the Xiaojiang fault zone into the Yangtze Craton as depth increases.Through our velocity model,we think that southeastern Tibet is undergoing three different tectonic modes at t

关 键 词：Southeastern Tibet Surface wave tomography Shear wave velocity structure Xiaojiang fault system Emeishan large igneous province Asthenospheric upwelling 

分 类 号：P315[天文地球—地震学]