东海与黄海的三维速度结构及其构造意义

3D VELOCITY STRUCTURE AND ITS TECTONIC IMPLICATIONS IN THE EAST CHINA SEA AND YELLOW SEA

利用面波层析技术分析了该区地壳上地幔的三维构造。地壳上层的速度分布具有以海域中心为轴,东西两侧对称的特点,总体呈NE向展布,同结晶基底的构造对应良好。东海与黄海的构造差异主要表现在下地壳与上地幔,分别与华北和华南的速度结构相同。从杭州湾到吐噶喇海峡(大约沿30°N纬线)存在一条近EW走向的上地幔高速带。东海与黄海在地貌与地质、地震活动、大地热流、品质因数和重磁异常等方面存在系统性的差异,这与早第四纪从杭州湾到吐噶喇海峡出现的左旋剪切破裂以及贝尼奥失带的右旋撕裂有关。作者推断:东海是新生代弧后扩张作用而形成的;大巴-大别山南麓-杭州湾-吐噶喇海峡是华北与华南地壳块体的分界线,琉球海沟的消减带是华南地壳块体的东界;东亚的现代构造运动,主要与太平洋板块、印度板块和上地幔的运动有关,而菲律宾板块的俯冲对中国大陆的作用较小。

3D structure of the crust and upper mantle in the studied area has been analyzed from: surface wave tomography. The velocity distribution in the upper-most crust is symmetrical on two sides of the central line of the sea, and coincides with the structure of crystalline basement. The essential difference in tectonics between the East China Sea and the Yellow Sea mainly lies in that the velocity structures of their lower crust and upper mantle are identical to those of South China and North China. In the upper mantle there exists a highvelocity zone with a nearly EW strike from the Hangzhou Bay, China, to the Tokara Channel, Japan, along about the latitude of 30°. It is found that between the East China Sea and the Yellow Sea there are systematical differences in geomorphology, geology, seismicity, heat flow, quality factor and gravity and aeromagnetic anomalies, which is related to both left-lateral shear dislocation and right-lateral tear of the Benioff zone from the Hanzhou Bay to the Tokara Channel. It is noted that,he crustal structures in the East China Sea and Yellow Sea are quite complicated, with the NE trend predominating at the shallow levels and the NW trend predominating at the deep levels, like grade separation. It is inferred that the East China Sea was formed by Ceonozoic back-arc extension. The boundary between the North China and South China crustal blocks stretches along the southern piedmont of Mts. Daba-Dabie—Hangzhou Bay—Tokara Channel, and the snbduction zone at the Ryukyu trench is the eastern boundary of the South China crustal block. The movements of the Pacific plate, Indian plate and upper mantle rather than the Philippine plate subduelion have played a dominant role for the modern tectonic movements.