The No. 5 fault zone in Shunbei area, a main strike-slip fault zone running through two paleo-uplifts and being devided into north, middle, south and uplifted segments, has always been the focus of research on the formation and evolution of the strike-slip fault system in Shunbei area and its surroundings. In this study, the latest high-precision 3D seismic data newly acquired and processed are applied to carry out the fine analysis of the uplifted segment of the No. 5 fault zone in Shunbei area, determining its geometric and kinematic characteristics and revealing its formation and evolution process. According to the change of strike angle and segmented deformation pattern, the uplifted segment of the study area can be divided into three sections: the north translational section (NE16°) (uplifted segement Ⅰ), the middle pull-apart section (NE19°) (uplifted segment Ⅱ), and the south compressional-uplifted section (NE25°) (uplifted segment Ⅲ). The uplifted segment in the study area develops a layered deformation pattern composed of high and steep strike-slip faults and multiple suites of en echelon normal faults from bottom to top, while undergoing multistage strike-slip activities during the Middle Caledonian, Late Caledonian, Middle-to-Late Hercynian and Indosinian-Early Himalayan periods. In the study area, the strike-slip activities feature “strong in the segments Ⅱ and Ⅲ, weak in the segment I”. Under the influence of stress transmission from south to north, the south and uplifted segments present sinistral strike-slip from south to north with No. 1 fault zone in Tazhong area as the boundary at the initial stage of development, while the north and middle segments present dextral strike-slip from north to south, with the maximum principal stress deflecting from NW to NE. After the Late Caledonian period, the No. 5 fault zone in Shunbei area presented sinistral strike-slip as a whole, while during the Indosinian-Early Himalayan periods, the uplifted segment reversed to dextral strike-slip, with the maximum principal stress reversing from NW to NE.

In this paper we use the new brittle faulting theory,the "non-coordination criteria",to expound and analyze the mechanical mechanism of basement pre-existing fabric controlling fault formation and evolution,to determine the law of change in pre-existing basement fabric activity,and to investigate the controlling role of basement pre-existing fabric on fault formation and evolution.Through the study we came to the following conclusions.(1)The basement pre-existing fabric(particularly the pre-existing fault)has priority in activity,which is the root cause of its control over fault formation and evolution in sedimentary basin.(2)The controlling power of pre-existing fabric on basin faulting is determined by its activity that is controlled by the attitude and mechanical property of the pre-existing fabric,as well as its stress state,and its activity can be quantitatively described using the activity coefficient(fAS)of pre-existing fabric.(3)The faults controlled by basement pre-existing fault exhibit remarkable regularity in their locations and trends(strikes),formation orders,inherited features,and the size distributions.(4)The controlling power of basement pre-existing fault is the strongest when the fault is perpendicular to the extension direction of the controlled fault and the angle between the pre-existing fault and the σ1 of the controlled fault is 45°-(/2);when the angle(α)between the strike of the pre-existing fault and the extension direction of the controlled fault becomes smaller gradually,and the dip-angle deviated from 45°+(/2),the controlling power will be reduced progressively.(5)The larger the size of the pre-existing fault is,the more intensive the controlling power of the pre-existing fault on fault formation and evolution will be.The faults controlled by large-scale pre-existing basement faults tend to constitute the structural framework in rift basin.(6)When the shear strength becoming smaller,the possibility of the occurrence of the rupture in the pre-existing weak-zone will be increasing,and its controlling power will steadily be enhanced,but its affection is relatively weak comparing to the basement pre-existing fault.Using the above-mentioned conclusions,a theoretical model for the structural interpretation of seismic data may be constructed.These conclusions may also be used as a theoretical guidance for in-depth study of fault system formation and evolution in rift basin.