中国东部海域及邻区岩石层地幔的P波速度结构与构造分析

P wave velocity structure and tectonics analysis of lithospheric mantle in eastern China seas and adjacent regions

利用中国大陆东部及台湾地区、日本和琉球群岛的地震观测数据,通过体波地震层析技术反演了中国东部海域及其邻近地区的P波速度结构.以此为依据分析了不同地区的岩石层性质和深部动力学条件,探讨了中朝与扬子块体、扬子与华夏块体在海区的深部边界及其构造属性,揭示出菲律宾海板块与欧亚大陆的碰撞以及板片俯冲下沉、弧后扩张作用对中国东部海域岩石层结构的影响.结果表明,中国东部海域的岩石层地幔存在明显的横向非均匀性,它们与区域构造的形成演化有一定的联系.中国大陆东部的五莲-青岛断裂与朝鲜半岛西缘断裂、济州岛南缘断裂共同构成中朝和扬子块体的边界,江绍断裂向东延伸至朝鲜半岛南端成为分隔扬子和华夏块体的边界;东海陆架与冲绳海槽的岩石层结构差异明显,东海陆架具有中国东部地区的岩石层特征,属于欧亚大陆向海域的延伸;冲绳海槽的岩石层强烈减薄,为大陆向大洋过渡的区域;沿着日本-琉球-台湾俯冲带,菲律宾海板块俯冲下沉引起的地幔扰动对中国东部海域产生了较大的影响,欧亚大陆与菲律宾海板块之间的相互碰撞导致台湾地区岩石层明显增厚.

Using P wave arrivals from the earthquakes recorded by seismic stations in Taiwan and the mainland of China, Japan and Ryukyu Arcs, we reconstructed the velocity structure of the lithospheric mantle in the eastern China Sea and adjacent area by a travel time tomography technique. Based on the result, we analyzed the deep boundaries between the Sino-Korea, Yangtze, and South China blocks and determined their tectonic properties by comparing lithosphere mantle structures and dynamic conditions. They also revealed the interaction between the Eurasian continent and the Philippine Sea plate in Taiwan and the effect of slab subduction and back-arc extension along the Ryukyu Arc on the lithosphere structure in the eastern China Sea areas. The results indicate that the boundary in the sea areas between the Sino-Korea and Yangtze blocks mainly consists of the Wulian-Qingdao fault in eastern China, the western marginal fault of the Korea peninsula, and the southern marginal fault of the Cheju island. The Jiangshao fault is extended to the south tip of the Korea peninsula and serves as the boundary to separate the Yangtze and south China blocks. A clear difference of lithosphere structure is observed in the continent shelf of the eastern China Sea and the Okinawa through. The former has a nature of the lithosphere of eastern China and belongs to an extension of the Eurasian continent. The lithosphere of the latter is thinned intensively as a transition area from continental to oceanic lithosphere. Along the Japan-Ryukyu-Taiwan subduction zone, a mantle perturbation produced by the downgoing slab of the Phlippine Sea plate plays an important role in the eastern China sea areas. The interaction between the Eurasia continent and the Philippine Sea plate resulted in the thickening of the lithosphere beneath Taiwan.