基于背景噪声反演华南块体岩石圈三维S波速度结构

3-D S-wave Lithosphere Structure of South China Block Based on Ambient Noise Tomography

利用背景噪声方法,对布设在华南块体及其周边区域数个流动地震台阵中共704个地震台站的连续数据进行分析,反演得到华南岩石圈的三维S波速度结构。结果表明,地表附近S波速度结构与华南块体的地表构造高度相关,低速异常区集中在四川盆地和江汉盆地等沉积层较厚的区域。江南造山带的中上地壳呈现明显的高速异常,该高速异常即为华夏块体与扬子块体的分界区域。华夏块体中地壳低速异常区与该区域广泛分布的中生代花岗岩对应较好。华南上地幔岩石圈的东部与西部存在显著的速度差异,西部呈现显著的高速异常,反映西部四川盆地底部稳固的克拉通结构;上地幔的低速异常揭示华南东部岩石圈因太平洋板块俯冲的影响而明显减薄(<70km)。推测华夏块体以琼州海峡为中心的上地幔显著低速区可能对应海南地幔柱的热物质上涌。

Using continuous records of 704 stations from several mobile arrays,high-resolution S wave velocity structure of South China Block(SCB)was obtained by ambient noise tomography.In 3-D S wave velocity model,the velocities in shallow crust are well consistent with the surface geology and low velocity anomalies concentrate in Sichuan Basin and Jianghan Basin.The boundary between Yangtze Block and Cathaysian Block can be identified by a high-velocity belt in crust,which is Jiangnan Orogeny generated in collision.The low velocity anomaly of Cathaysian Block in middle crust is related to the widespread Mesozoic granite.In upper mantle,there are significant differences between the east and west South China Block:the west South China Block presents a significant high velocity anomaly which reflects a stable craton in Sichuan Basin;the low velocity anomaly in east South China Block reveals that the lithosphere has been thinned(<70 km)by the subduction of paleo-Pacific Plate.Besides,it is speculated that the low velocity anomaly of Qiongzhou Strait in upper mantle may correspond to the Hainan plume.