Research Of Late Mesozoic Extensional Tectonics In Chicheng Area, North Hebei Province

Extensional deformations in North China Craton during the late Mesozoic areimportant evidences of lithosphere delamination. Detachment faulting in shallowcrust level evidences this stretching process. Normal faults, which could usually befound in the margin of subsidence basins, remain as upper part of the detachmentfaulting. Research of shallow level extensional tectonics in North China Craton isscant, and this is especially the case in western Yanshan area and northern HebeiProvince.This paper mainly focuses on research in Chicheng area, aiming to have afurther understanding of extensional tectonics other than Metamophic Core Complexin later Mesozoic. The research will also concern about the interplay andcharacteristics of NNE Taihang tectonics and EW Yanshan structural belt and itsdeformational pattern is nearby area.Conclusions of this research are listed as following:(1) In northern Hebei Province, especially Chicheng area, stretching tectonicsmainly consists of subsidence basins and high-angle normal faults in basin margins.Although marginal normal fault of Diaoe half graben, dips to NWW, and marginalcontrolled-normal fault of Qingyanggou half graben, dips to SEE, oriented withdistinctive extensional direction, they actually indicate the same extensionalenvironment.(2) Interior and marginal district of half graben preserve secondary extensionalstructures. These structures such as step-normal fault systems and minor host-grabencombinations are important elements of extensional tectonics(3) Marginal normal fault decreases its displacement from the center point totwo ends, which could be supported by the preservation of Jiufoutang sedimentation.In Diaoe basin, Jiufoutang Formation could only be found in the middle portion ofthe marginal normal fault controlled basin area. This phenomenon reflects thatnormal faults developed synchronologically with Jiufoutang sandstone.(4) Geometry and kinematics of marginal-controlled normal fault systems in northern Hebei Province, especially Chicheng area, indicate that they tectonicallybelong to Huangqi-Wulonggou fault belt. These normal fault systems are geneticallyrelate to Taihangshan normal fault system. Generally, NNE tectonics of Taihangshanstrikes northward and reached Yanshan area, cutting EW Yanshan tectonic belt.Therefore, NNE normal fault system in Yanshan belt dominated the earlier basindevelopment.(5) Comparison of late Mesozoic stretching tectonics in eastern and middle partof Yanshan area provides that structural styles, deformational sequences and tectoniccharacteristics hold the many similarities. Integrating chronology studies of nearbyareas with structural analysis of Diaoe and Qingyanggou basin confirms thatextensional subsidence basin in Chicheng area happened in early Cretaceous.Marginal controlled-normal faulting occurred earlier than this time.