Geometry and kinematics of the southern Junggarthrust and fold belt, northern Tian Shan

The southern Junggar fold-and-thrust belt (SJFTB) along the TianShan northern piedmont contains a record of the interactions between the TianShan Mountains and the Junggar Basin during the Cenozoic. Our researcher shows shortening distribution and growth structure along thrust fault can be very helpful in recognizing geometry and kinematic variations of thrust sheet. At the foothill of the northern TianShan a set of high-amplitude anticlines are growing by complex seismically active break-forward ramping and wedging in the thrust sheet as it steps up from a regional Jurassic coal detachment to the basal Cenozoic mudstone detachment. In the eastern part of foothill, a basement-involved structural wedge developed with21km shortening in the thrust sheet. The shortening of Junggar Basin is only 2km. In the western part of foothill, a complex anticline is growing with a total of 15 km shortening by two-stage structural deformation that structural wedge was followed by fault-bend fold, and 7km shortening has been transferred towards the interior of the Junggar Basinto form two rows of folds. The onset and translation of thrust sheet into the Junggar Basin is constrained by growth strata.We have determined the ages of growth strata by tying the seismic grid to published outcrop magnetostratigraphic sections in the Junggar Basin. The structural wedge was growing along the TianShan foothill in earlier than 23Ma, and thrust faults transferred towards the Junggar Basinsince 8Ma. The total estimated shortening of SJFTB is 15-23km, and has an average shortening rate of 1 ± 0.4 mm/yr. This study would be helpful in better understanding the geometry and kinematic evolution and seismic hazard assessments of the SJFTB.