远震剪切波分裂研究华南西南部上地幔各向异性特征  

Upper mantle anisotropy beneath the Southwestern South China Block revealed by teleseismic shear wave splitting measurements

作　　者：王祎然 滕吉文[1,2] 田小波 WANG YiRan;TENG JiWen;TIAN XiaoBo(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of Chinese Academy of Sciences,Beijing 100049,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [2]中国科学院大学,北京100049 [3]中国科学院地球科学研究院,北京100029

出　　处：《地球物理学报》2024年第3期829-842,共14页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(42174116,42030308和41974053)资助。

摘　　要：华南板块由扬子克拉通和华夏地块在新元古代碰撞拼合形成,其西南部的缝合带位置存在强烈争议.本文基于一条南北向宽频带流动台阵天然地震数据,利用SKS波分裂研究华南西南部上地幔各向异性特征的南北向变化.分裂测量结果显示,26°N以南的右江盆地快波偏振方向为E-W或NEE-SWW方向,分裂时差为0.5~2.5 s,变化范围较大;川东褶皱带存在较多空解,快波偏振方向以近东西向为主,分裂时差在0.5~1.5 s范围内变化;在右江盆地北缘和川东褶皱带的过渡区域(约26°N附近)各向异性明显较弱.结合前人的上地幔速度成像结果,我们认为川东褶皱带与右江盆地过渡带是扬子克拉通的南边界,在其下方北侧的川东褶皱带巨厚的岩石圈向南转变成较薄的岩石圈,陡变的岩石圈边界引起了软流圈上涌,软流圈的垂向运动导致其水平方位各向异性较弱.The South China Block is formed by the assemblage of the Yangtze Craton and the Cathaysia Block in Neoproterozoic, with a disputed southwest boundary location. Based on a north-south orienting broadband seismic array crossing the Youjiang Basin and the East Sichuan fold belt, we obtained the variation of seismic upper mantle anisotropy beneath Southwest South China Block by SKS wave splitting measurements. The results show from 26°N to south, the fast wave polarization direction of Youjiang Basin is mainly E-W and NEE-SWW, with delay time varying between 0.5~2.5 s. The upper mantle anisotropy of the eastern Sichuan fold belt includes many null values and its fast wave polarization direction is dominantly E-W, with delay time varying between 0.5~1.5 s. In the transition zone of the Youjiang Basin and the East Sichuan fold belt, the upper mantle anisotropy is obviously weak. Combined with previous study of upper mantle velocity structure, we suggest the transition zone between East Sichuan fold belt and Youjiang Basin is the south boundary of Yangtze Craton where the extremely thick lithosphere of the East Sichuan fold belt thinned down to the south. The sharp lithospheric boundary change induced the upwelling of asthenosphere whose vertically motion resulted in the weak horizontal azimuth anisotropy above the area.

关 键 词：剪切波分裂 方位各向异性 上地幔变形 扬子克拉通边界 

分 类 号：P313[天文地球—固体地球物理学] P315[天文地球—地球物理学]