CENOZOIC TECTONICS OF CHINA WITH EMPHASIS ON ITS EASTERN REGIONS AND EAST ASIAN OFFSHORE BASINS

China and its adjacent regions, including East Asian marginal seas, have experienced complex deformation since the Eocene. At that time the northward moving, anticlockwise rotating Indian plate collided with Asia at the Pamirs. That initial collision and the subsequent closure of neo-Tethys to the east led to the present complexity of East Asian geodynamics. Two factors control that complexity: (1) the reactivation of previous plate and intraplate tectonic boundaries; and (2) the eastward displacement ("extrusion") of areas E and NE of the Pamirs towards the Pacific ocean basin. The two factors were not independent of each other; the geometry of Pacific-ward displacement of China and environs was in large part controlled by pre-existing structural boundaries in the East Asian collage of native and accreted terranes. Intraplate ranges such as the Tianshan, Altai, Qinling, and Xing'an-Taihang Shan were strongly uplifted. Sedimentation in intervening basins helps record this history of intraplate fragmentation and orogenesis. For example, the 600 km-long S-shaped Wei River-Shanxi graben system within the North China craton is a series of en echelon NNE-trending grabens connected by NNE-striking dextral transcurrent faults. At its southern end, the Wei River graben contains a 6 km thick terrigenous sedimentary sequence initiated in the Eocene.

The differential displacements of East Asia towards the Pacific and the generally convergent interactions between the Eurasian and Pacific plates have led to separate and diachronous development of marginal seas between the two dominant plates. For example, the transcurrent rifting of the Sea of Japan led to the generation of oceanic lithosphere at least as old as 38 Ma. In contrast, the ensialic northern Yellow Sea formed at the beginning of the Cenozoic by extension of the Eurasian continental plate.

The current dynamic strain field of East Asia was previously defined by earthquake focal mechanisms, which are generally consistent with the much more sensitive vectors of GPS data measured during the 1990's. The Pacific-ward movement of much of Eastern Asia continues today, but its patterns are still governed in part by pre-existing intraplate boundaries.