Structural Geometry And Kinematics Of The Taihang Mountain Piedmont Fault And Its Controlling On The Development Of The Bohai Bay Basin

Located in the transformation zone of the Bohai Bay Basin and the Taihang Mountain Uplift,the Taihang Mountain Piedmont Fault(TMPF)serves as an important boundary of topography,geomorphology and tectonic division in eastern China.However,due to the limitation of data and its accuracy,the research on the TMPF is relatively weak.Studying on the geometry,kinematics of the TMPF and its controlling on the development of the basin is not only helpful to understand the temporal and spatial characteristics of the fault,but also of great significance to analyze the geologic structure and tectonic evolution of the adjacent basin.Besides,this study will also provide new clues for exploring the coupling relationship between the Bohai Bay Basin and the Taihang Mountain uplift.In this study,the Jizhong Depression and the TMPF developed on its west side are taken as the research objects.Based on the combination of regional geological,deep geophysical information and high resolution drilling and seismic data in the depression,the 2-D geometric features of the entire TMPF are summarized systematically using the method of structural analysis,and the 3-D geometry of the fault located on the west side of the Jizhong Depression is revealed.The kinematic characteristics of TMPF(Shijiazhuang-Xushui)are studied in detail through structural restoration.According to the stratigraphic characteristics and structural styles,the controlling effect of the TMPF on the development of Jizhong Depression is analyzed.Finally,combined with the deep geological background,the genetic mechanism of the TMPF is discussed.Drilling,seismic and geological data show that the strata developed in the Jizhong Depression and Taihang Mountain Uplift include Archean to Cenozoic.According to the regional unconformities identified in the study area,7 structural layers are divided.The TMPF,which appears as a large detachment fault,takes the shape of a typical listric fault in the section,and finally enters the detachment surface at the bottom of the upper crust.The depth of the surface is 5.5-6.5s in TWT.In the study area,the plane and 3-D characteristics of the fault change obviously along the strike.Comprehensive interpretation of the drilling and seismic data demonstrates that the TMPF in the study area experienced 2 extension phases of the Late Mesozoic and Paleogene as well as the tectonic inversion occurred at the end of the Paleogene.Based on the fine depiction of the growth strata,both of the extension phases are subdivided into 3 stages.Both phases are characterized by a gradual weakening in the extension and the rifting tends to migrate towards the north.On the basis of the analysis of fault geometry and kinematic characteristics,the TMPF in the study area is divided into the Shijiazhuang Fault,the Baoding Fault and the Xushui Fault according to the identified segmented signs.Study on the stratigraphic characteristics and structural styles shows that the differential activities of the TMPF control the development of the Jizhong Depression since the Late Mesozoic,and the controlling effect on different structural belts have obvious differences.Considering the deep geological background of the region,it is believed that the development of the TMPF acts as the shallow response to the large scale lithospheric thinning of the eastern North China Craton.