Analysis of Lithosphere Structure and Tectonics of Chinese Marginal Seas and Adjacent Regions

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 seismic tomography results of the Chinese marginal seas. The 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 continental shelf of the East China Sea 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. The analysis indicates that there is a deep tectonic boundary between the eastern Yellow Sea and the Korean peninsula, which roughly corresponds to the eastern Yellow Sea fault zone. Pn anisotropy variations on the east and west of the boundary also reflect deformation characters of the lithospheric mantle under different tectonic stress and fault shearing. Beneath the continental shelf of the East China Sea, low velocities reveal evidence of mantle activity during the formation of the pull-apart basin, which implies that a mantle upward probably occurred during the Mesozoic and Cenozoic times, and resulted in lithosphere 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. The continental margin of the northern South China Sea has a thicker and colder lithosphere mantle with lower temperatures. It is therefore estimated that the high velocity layers in the lower crust of the northern continental margin may have formed prior to the rifting of the South China Sea, and they probably represent the pre-existing materials during the formation of the original crust and mantle. However, the rifting of the central South China Sea basin has resulted not only in crustal extension, but the mantle upwelling has also caused the thinning or removal of the lithospheric mantle.