AN INDENTATION MODEL FOR THE NORTH AND SOUTH CHINA COLLISION AND THE DEVELOPMENT OF THE TAN-LU AND HONAM FAULT SYSTEMS, EASTERN ASIA

Passive continental margins are geometrically irregular as a consequence of either triple-junction evolution or the development of transfer zones in detachment fault systems, whereas active continental margins are smoothly arc-shaped due to subduction of plates on the Earth's spherical We propose that this basic difference in boundary geometry has played an important role in the latest Paleozoic-early Mesozoic collision of North and South China. In particular, we suggest that prior to collision, the active southern margin of the North China Block (NCB) was contiguous across die Qilian Shan, Qinling, Dabie Shan, Shandong peninsula of east central China to the Imjingang area of central Korea. The passive northern margin of the South China Block (SCB), in contrast, had a more irregular shape, such that its northeastern segment in northern Jiangsu and eastern Anhui provinces of China extended some 500 km farther north than its western counterparts in northern Sichuan, southern Shaanxi, and northern Hubei provinces. Collision of the NCB and the SCB began by indentation of the northeastern SCB into the eastern NCB in the late Early Permian and lasted until the Late Triassic-Early Jurassic. The indentation produced the left-slip Tan-Lu fault in northeastern China and the right-slip Honam shear zone in southeastern Korea and caused the northward displacement of the Shandong and the Imjingang metamorphic belts. This model predicts that collision along the Dabie and Qinling metamorphic belt occurred significantly later than along the Shandong belt, which is consistent with radiometric and depositional constraints on the time of collision. The proposed model accounts for the abrupt termination of the Tan-Lu fault at its south end and the drastic decrease in slip along the, Tan-Lu fault north of the Shandong metamorphic belt. The model also predicts the distribution and ages of metamorphism along the suture and the observed local but intense Triassic deformation (=Indosinian orogeny) in northeastern China and northern Korea, which was previously an enigmatic feature in this region.