Structural Analysis Of Kelamay-xiazijie Strike-slip Fault Systerms In NW Margin Of Junggar Basin,Xinjiang,China

The fault system in the NW margin of the Junggar Basin, west China, affords an exceptional opportunity to document the structural features of a major strike-slip fault using two-and three dimensional seismic reflection data and magnetotelluric(MT) data. The identifications of strike-slip are made not only from profile and map relationship but also from3D relationship of structural element. The growth stratigraphic sequence on the top or flank of en echelon folds provides a complete, decipherable record of the kinematics of strike-slip fault.The Xiahongbei and Kebai fault zone display relatively straight, narrow, long, throughgoing, solitary master fault or zone of deformation; narrow fault slices within the master fault zone that steepen and join at depth form positive flower structures; different orientation of relative upthrown side and separation sense at these fault slices; coeval, en echelon flanking folds and faults structures developed in the Xiahongbei fault zone.Xiahongbei fault zone can be divided into three tectonic units from north to south: the Halat basement uplift belt (Dalabute strike-slip fault), the Wuerhe-Xiazijie fault block-en echelon folds belt, and the Mahu lake slop were identified at the NW margin of the Junggar Basin. The Zayie-Halat uplift basement belt is closed to the Dalabute strike-slip fault and developed vertical strike-slip faults. Devonian to Upper Carboniferous volcanic, volcaniclastic and flysch rocks crop out along the belt. The Wuerhe-Xiazijie fault block-en echelon folds belt consists of slip faults and en echelon folds. The stepping fault patterns and orientation of en echelon fold structures indicate right-lateral sense about W-E azimuth of slip. The fault segments with clockwise orientation are characterized by convergent structures. Xiahongbei strike-slip fault is accompanied by a horsetail splays reverse faults at its end tips in the Hongqiba area. The Carboniferous, Permian and Triassic have folded and are unconformity by the Jurassic and Cretaceous, indicating the deformation developed in the Late Permian to Triassic.In the Basement, Kebai fault zone present a stepover between two NNE offset fault and produce pop-ups and uplifts in the Baikouquan area. Similarly, In the Permian to Triassic sediment cover, it can be divided into three different Structural deformation sections. Both concave and convex-up oblique reverse faults in the pop-up link the principal deformation zone (PDZ) and represent a series of sigmoidal dextral reverse fault on the3D seismic horizon time slice. The unconformity between late Permian wuerhe formation and Triassic formation and the growth stratigraphic sequence in Triassic show Kebai fault zone deformed during the Late Permian to the Triassic.According to the structural stress fields in NW margin of Junggar basin and adjacent areas and the map relationship of Xiaohongbei fault, Kebai fault and Dalabute fault, these faults comprise a Riedel model of right simple shear in the Late Permian to Triassic and Dalabute represents a dextral fault system, but presently is a sinistral strik-slip faul system. There may be a slip-reversal of Dalabute fault during The Jurassic accompanied by stretching, subsidence and formation of rift basin in The Hesituoluogai area north of it. The maxium principal stress orientation is N76°W in the Late Permian to Triassic, but near SN after The Jurassic. The exposed Dalabute fault has been reactivated in the Cenozoic, which was affected by the long-distance expression of the Cenozoic India-Asia collision. The NW margin of the Junggar Basin apparently was not defonned in the Cenozoic.