Cordilleran Section - 97th Annual Meeting, and Pacific Section, American Association of Petroleum Geologists (April 9-11, 2001)

Paper No. 0
Presentation Time: 11:10 AM


ZHANG, Changhou, SONG, Honglin, WANG, Genhou and SUN, Weihua, Dept. of Geology, China Univ of Geosciences, Beijing, 100083, China,

An east-west dextral strike-slip system has been recognized in the middle part of the Mesozoic intraplate Yanshan orogenic belt of northern China. This fault system is composed of two east-west oriented master fault zones -- Gubeikou-Pingquan to the north and Miyun-Xifengkou to the south. These fault zones lie about 40 km apart and are characterized by right stepping en echelon fault segments. Structures that lie between the master zones include northeast striking contractional faults and associated folds, and northwest striking extensional faults and dykes. The extensional structures are inferred to be comparable to "T fractures" of Riedel strain models. The northeast oriented contractional faults and associated folds between the two master east-west faults are interpreted as the counterparts of compressive structures in Riedel models. Collectively, these structures define a regional dextral shear system that formed in latest Jurassic to earliest Cretaceous time.

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.