Cenozoic tectonic evolution and the 3D structure of the lithosphere of the South China Sea.

Abstract

Seismic tomographic data indicate that the lithosphere velocity is low in the South China Sea region from the mouth of the Red River (Hong Ha River) through the South China Sea and Sulu Sea to Sulawesi Sea. The velocity of the transverse wave at the base of the lithosphere is only 4.4 km/s and the thickness of the lithosphere ranges from 60 to 80 km; so the region is the one with a thin lithosphere. The velocity of the asthenosphere is also relatively low, ranging from 4.2 to 4.4 km/s, but its thickness is great, 200 km. From the Red River-Yinggehai fault belt through the South China Sea to the Sulu Sea there exists a NW-trending, ～200 km wide, upper mantle low-velocity zone with a transverse wave velocity ranging from 4.05 to 4.25 km/s. The above-mentioned data suggest that there exists a gigantic low-velocity zone from the margin of the East Asian continent to marginal sea. It strikes NW in the South China Sea region and NNW in the East China Sea region. The approximate consistency of these strikes with those of the lineaments on the surface reflects that the Cenozoic tectonic activity there might be related to the distribution of the mantle low-velocity zone, i.e. the upper mantle low-velocity zone reflects the regional flow of the lithosphere, which gave rise to tensional tectonics in the superficial layer of the lithosphere and formed rifts and slightly later sea-floor spreading and a number of marginal sea basins on the eastern margin of Asia.