Mesozoic Strike-slip Structures And Tectonic Evolution Of Hong-Che Fault Zone In The Northwest Margin Of Junggar Basin, Xinjiang, China

The Central Asia Orogenic Belt (CAOB) or the Alatids was formed in the Paleozoic resulted from a series of subduction-collision-accretion processes. The deformation history of the CAOB since the Permian remains poorly understood due to multi-phases deformation, especially the widely developed tectonics in the Cenozoic. The Hong-Che fault system is located at the northewestern Junggar basin, serves as the coupling area between the Junggar basin and the West Junggar unit, experienced multi-phases deformation which has been recorded in the sediments of the basin range. Moreover, several kilometers of thick Cretaceous-Cenozoic sediments without distinctive tectonic deformation overlay the Pre-Cretaceous structures, makes it a nice place to study the characteristic, kinematic and the structural evolution of the CAOB.In this study, we focus on the geometry of structures in Hong-Che fault system by using both 2D and 3D seismic reflection data, as well as the structural restoration method. The analytic results demonstrate that:(1) The Hong-Che fault was a right-lateral strike-slip fault system. It is characterized by master strike-slip fault with contractional thrust faults and fault-related folds developed within the restraining bend of the southern segment of the Hong-Che fault zone. Relatively straight, throughgoing, solitary master fault developed within a narrow deformation zone along strike in the middle segment of Hong-Che fault zone. The gently disappeared Hong-Che fault accompany with a serious of horsetail splay of reverse faults developed in the northern fault tip area of Hong-Che fault zone. The structural characteristic vaires along the Hong-Che fault system, but the kinematic is consitent, which makes it a dextral strike-slip fault system.(2) The 3D strucutral restoration conducted in the Hong-Che area indicates its oblique compressional kinematic. Both the results of dilatation and the restorational vector of the structural restoration indicate the deformation is relatively weaker in the Middle segment and more intense in the South segment, and a SW-NE oblique compressional kinematic. Based on the analysis of the cutoff between the origin strucutral surface and the restored strucutral surface, a method of predicting direction of the regional movement is proposed and testified by forward modeling. The movement direction of the western Junggar basin with respect to Chepaizi Uplift is 210°～230° according to the result of this method.(3) The dextral strike-slip faulting has taken place during the Middle-Triassic and the Jurassic. The contact between the strata and the faults as well as the growth strata developed in the related structures in the region revealled by the seismic profiles indicates the major deformation timing is Middle-Late Triassic, with reactivation in the Jurassic. The consistent deformation timing demonstrates the Hong-Che fault region to be a strike-slip fault system.(4) Multiple deformation phases have been indicated by the synkinematic growth strata including the Early Permian regional extension, the Late Permian tectonic inversion and the strike-slip deformation from Mid-Triassic to Late Jurassic.(5) The demonstrated dextral strike-slip faulting is consistent with the Middle Triassic-Jurassic deformation in the Ke-Bai, Wu-Xia, Dalabute and Irtysh fault zones, and therefore supports the counterclockwise rotation of Junggar Basin.