Folding And Thrusting Events And Stratigraphic Record In The Northern Taihang Mountain

The NNE-trending Taihang Mountain is an important tectonic deformation zone in the east of China. As to geographical location, The Taihang Mountain lies between the Ordos Basin to the west and the Bohai Bay Basin to the east. The northern Taihang Mountain is connected with Yinshan-Yanshan intraplate deformation zone in the north, and the south end joins the Qinling-Dabie orogenic belt. Because of its particular structural distribution and deformation pattern, it is defined as Taihang Mountain structural deformation belt.The research area is located in the northern part of the Taihang Mountain, including the area between south of Changping-Yangyuan-Datong line and north of Shijiazhuang-Xinzhou-Jingle line. The research object of this paper are NE-trending thrust faults and Jurassic basins. Based on the coupling relationship between basin and orogenic belt, this study combines basin and mountain,as well as deposition and tectonics. In order to comprehensively discuss the law of development and evolvement in the Taihang Mountain area during Jurassic, the method of thermal geochronology is also used.The basic tectonic framework of NE-trending thrust faults in research area is as follows:(1)thrust faults are mainly distributed in relatively concentrated strip area. The tectonic deformation is very weak between thrust fault belts. There is a macroscopic tectonic framework with the alternating distribution of strong deformation and weak deformation on a regional scale; (2)thrust faults control the exposing and distributing configuration of the related stratum, and result in large scale uplifting of the basement metamorphic rock series; (3)the main thrusting direction in north area is from southeast to northwest, whereas the main thrusting direction in north area is from northwest to southeast. There are backthrusts in local area.This paper conducts provenance analysis on sediments obtained respectively from western Datong basin and Ningwu-Jingle basin, central Zhaobai basin and eastern Jingxi basin. Together with the data from isotope chronology and geochemistry, the analysis results indicate that with the effect of compression in NW-SE direction, fold deformation in the Taihang Mountain area has occurred since the turn of middle-late Jurassic(ca.175Ma), and lasted about 20Ma at least. The compression in NW-SE direction reached its climax during the end of late Jurassic to the beginning of early Cretaceous, which resulted in a strong deformation process from folds to thrust faults. The early fold deformation process could be divided into two stages according to the contact relationship between strata. The first fold deformation occurred before Tiaojishan Formation, and the second one occurred at the turn of Tiaojishan Formation and Tuchengzi Formation. With respect to the big Ordos Basin, the continuous uplift in the Taihang Mountain area indicated a gradual shrink to the west in the eastern margin of it.During middle and late Jurassic, the structural evolution of North China block was contorled by multiple remote compressive stress, whereas the northwestward subduction of the Izanagi plate played a key role on the evolution of North China block, just like a kind of "activator", activating the old basement weak zone under the Taihang mountain area, resulting in a strong intraplate contraction deformation and uplift.