THE MIDDLE JURASSIC INTRACONTINENTAL DEFORMATIONAL EPISODE OF THE YANSHAN REGION, NORTH CHINA:IMPLICATIONS FOR THE TECTONIC EVOLUTION OF EAST ASIA

The intense intracontinental deformation occurred in the Middle Jurassic contributed mainly to the Mesozoic tectonic evolution of Yanshan region, although thrusting was still active in the region during the late Jurassic. This deformational episode, known as "Yanshanian Movement", can be recognized in western Beijing and western Liaoning, where two Jurassic sedimentary basins, the western Beijing basin (West Hills basin) and the Niuyingzi Basin, western Liaoning, documented that the deformational episode took place in the Longmen-Jiulongshan phases, the Middle Jurassic("pre-161 Ma event", Davis et al., 1998), and resulted in intense folding and thrusting of the region. In this paper, I present the evidence from the two basins to demonstrate that this intense E-W trending intracontinental deformation occurred in the Middle Jurassic, which synchronized with the closure of the Mongolo-Okhotsk Ocean, postdated suturing between the South China Block (SCB) and the North China Block-Mongolia Block (NCB-MON), and antedated the influence exerted by subduction of the the Pacific plate beneath eastern Asia on the region. That is, the Middle Jurassic deformational episode of the Yanshan region is corresponding to assembly of NCB-MON and the Siberian Block, rather than Pacific-East Asia interactions.