中国边缘海域及其邻区的岩石层结构与构造分析

利用中国边缘海域近年的地震层析成像结果,根据速度异常和各向异性分析东海、黄海和南海北部的岩石层结构和构造,讨论中朝块体和扬子块体在黄海内部的拼合边界(黄海东部断裂带)、东海陆架盆地上地幔异常与岩石层形成演化、南海北部地壳底部高速层的成因及地幔活动等问题。分析表明,黄海东部与朝鲜半岛之间存在一个深部构造界限(大致对应于黄海东部断裂带),分界两侧Pn波速度各向异性存在明显差异,反映不同构造应力和断裂剪切运动作用下的岩石层地幔变形特征。东海陆架下方的低速异常揭示了张裂盆地形成时期的地幔活动痕迹,表明中、新生代期间发生过地幔上涌并造成岩石层减薄,菲律宾海板块向西俯冲引发的地幔活动对东海陆架岩石层的形成、演化产生明显的影响。南海北部岩石层厚度较大并且温度相对偏低,地幔异常仅限于局部地区,估计南海北部大陆边缘的地壳底部高速层形成于张裂发生之前,或者是地壳形成时期壳幔分异时的产物。南海中央海盆的扩张不仅导致地壳拉张,软流层物质上涌,而且也造成岩石层地幔减薄甚至缺失。

Analysis of lithospheric structure and tectonics of the Chinese marginal seas and adjacent region.

Lithospheric structure and tectonics of the East China Sea, Yellow Sea and northern South China Sea are analyzed, based on the velocity anomaly and anisotropy from the results of seismic tomography in Chinese marginal seas.Our discussion is focused on the location of the collision boundary between the Sino-Korea and Yangtze blocks in the Yellow Sea, the unusual upper mantle beneath the East China Sea continental shelf and its lithospheric formation and evolution, the cause of the high-velocity layer in the lowermost crust and the mantle activity beneath the northern South China Sea.Analysis indicates that there is a deep tectonic boundary between the eastern Yellow Sea and the Korean Peninsula, which is roughly corresponding to the eastern Yellow Sea fault zone.The difference of the Pn anisotropy between the east side and the west side of the boundary also reflects the deformation characteristics of the lithospheric mantle under different tectonic stress and fault shearing.Beneath the East China Sea continental shelf, the low velocities reveal the evidence of the mantle activity during the formation of the pull-apart basin, which implies that a mantle upward probably occurred during the Mesozoic and the Cenozoic, and resulted in the lithospheric thinning.Obviously, the mantle activity caused by the westward subduction of the Philippine Sea plate has a significant influence on the formation and evolution of the lithosphere of the East China Sea continental shelf.In the northern South China Sea, fast Pn velocity indicate a thick lithosphere with lower temperatures.It is therefore estimated that the high-velocity layers in the lower crust of the northern continental margin may be formed prior to the rifting of the South Chine Sea and that probably they represent the materials produced during the formation of original crust and mantle.However, the rifting of the central South China Sea basin has resulted not only in the crustal extension and the mantle upwelling but also in the thinning or removal of lithospheric mantle.