TECTONIC IMPLICATIONS OF A JURA-CRETACEOUS DEXTRAL SHEAR SYSTEM IN THE INTRAPLATE YANSHAN OROGENIC BELT, NORTHERN CHINA
The dextral shear system is most clearly defined in eastern Hebei province, but we believe it continues eastward into Liaoning province and westward to northwest Hebei province. The system appears to merge in both eastern and western regions into distributed northeast-trending zones of thrust faulting. The eastern thrusts are predominantly southeast directed, whereas thrusts at the western end of the inferred shear zone are predominantly northeast directed. It is reasonable to infer that in latest Jurassic-earliest Cretaceous time the tectonic framework of the intraplate Yanshan orogen was dominated by east-west dextral strike-slip faulting. Both the Gubeikou-Pingquan and Miyun-Xifengkou fault zones were originally formed during Mid-Proterozoic continental rifting. Intraplate northwest-southeast contraction in Jura-Cretaceous time may be responsible for the dextral shear reactivation of these older structures. This deformational phase predated regional NW-SE Cretaceous extension (after ca 120 Ma) in the Yanshan -Yinshan belt and neighboring areas.