华南地区上地幔P波三维速度结构和动力学意义:来自有限频层析成像的证据  

3D velocity structure of upper mantle beneath South China and its tectonic implications:evidence from finite frequency seismic tomography

作　　者：曲平 陈永顺 于勇 盖增喜[1] 李秋生[3] 董树文[3] QU Ping;CHEN YongShun;YU Yong;GE ZengXi;LI QiuSheng;DONG ShuWen(Department of Geophysics,Peking University,Beijing 100871,China;Department of Ocean Science and Engineering,Southern University of Science and Technology,Shenzhen Guangdong 518055,China;China Deep Exploration Center,Chinese Academy of Geological Sciences,Beijing 100037,China)

机构地区：[1]北京大学地球与空间科学学院地球物理研究所,北京100871 [2]南方科技大学海洋科学与工程系,深圳518055 [3]中国地质科学院地球深部探测中心,北京100037

出　　处：《地球物理学报》2020年第8期2954-2969,共16页Chinese Journal of Geophysics

基　　金：地质科学院地质调查项目(DD20160082);国家自然科学基金重大项目(41890814)资助.

摘　　要：利用155个宽频带流动地震仪记录的连续地震波形数据,通过有限频层析成像技术,反演获得了华南地区上地幔的高分辨率P波三维速度模型.结果显示,大致以江南造山带为界,研究区域南部的华夏块体的大部分区域上地幔存在一个清晰的低速异常构造,而研究区北部的扬子克拉通的大部分区域上地幔则存在高速异常结构,并且这些速度异常体都向下延伸到地幔转换带.一个重要的结果是在(27°N,118°E)处观测到通过410-km界面的上涌流,并且在上升的过程中逐渐向西和向北扩展,显示为华夏块体深部200~400 km深度的大范围低速异常,可能为华夏块体广泛分布的新生代岩浆活动提供深部来源.更重要的是华夏块体通过410-km界面上涌流在上涌的过程中向北延伸,越过江南造山带“侵入”到扬子克拉通的南部地区,造成了扬子克拉通较厚的岩石圈对应的高速异常体向南倾斜的假象.最后,位于117°E(郯庐断裂的南端)以东的扬子克拉通岩石圈已经被“活化”,即被来自南部热的软流圈物质替而代之.同时,推断在华夏块体下方地幔转换带内低速异常体可能是与海南地幔柱有关.海南地幔柱和(27°N,118°E)410-km界面上涌流的关系还有待于今后更大范围地震台阵反演研究进行验证.We present three-dimensional high-resolution V P velocity model of the upper mantle beneath South China from finite-frequency tomography using seismic data recorded at 155 portable seismic stations in the region.The model shows a clear low-velocity anomaly in the upper mantle of most parts of the Cathaysia Block and a high-velocity anomaly in the upper mantle beneath the Middle Yangtze Craton,which are separated by the Jiangnan orogenic belt.Both these velocity anomalies can be traced down to the upper mantle transition zone.An important result is that an apparent upwelling(with a strong slow velocity anomaly)through the 410-km interface is observed in an area centered at latitude of 27 degrees north and longitude of 118 degrees east.This upwelling gradually expands westward and northward as it rises,resulting in a large-scale low-velocity anomaly at the depths of 200~400 km in the Cathaysia Block.This large-scale of low-velocity anomaly may provide a mantle source for the Cenozoic volcanism that was widely distributed in the Cathaysia Block.More importantly,the upwelling beneath the Cathaysia Block extends northward,beyond the Jiangnan orogenic belt,then into the southern part of the Yangtze Craton lithosphere.It caused the illusion that the Yangtze Craton′s thicker lithosphere tilted southward.Finally,the eastern part of the Yangtze Craton lithosphere,east of longitude of 117 degrees east(the southern end of the Tanlu fault zone),has been“re-activated”,replaced by the hot asthenosphere from the south.We speculate that the low velocity anomaly in the upper mantle transition zone below the Cathaysia Block may be related to the Hainan mantle plume.The relationship between the Hainan mantle plume and the(27°N,118°E)upwelling zone at the 410-kilometer interface remains to be verified in the future by larger-scale seismic array studies.

关 键 词：华南 速度结构 成像 有限频 海南地幔柱 

分 类 号：P315[天文地球—地震学]