TECTONIC FEATURES OF THE FORELAND OBDUCTION ZONE IN THE HETIAN SAG OF THE SOUTHWEST TARIM DEPRESSION

The foreland obduction zone of the Hetian Sag is located in the eastern of the Southwest Depression of the Tarim Basin.On the section,it consists of a superimposed anticline double tectosome overlapped by a nappe and many thrust sheets and a weakly deformed autochthon from upper to lower and from south to north.The nappe is 5000-7000m thick,205km long from east to west and 14-43km wide from south to north.Its northward displacement distance is 40-100km.It is a hinge folded anticline related to hanging-wall growth faults,and is controlled by Hetian large-scale step-typed decollement faults.On the lateral border of the nappe,lateral and oblique fault-slope secondary fault-related folded anticlines parallel to boundary faults were developed.On the front margin of it,a series of secondary faults and related folds were generated because the axis plane along the northern limb of the nappe anticline fractured.Within the internal of the nappe,rolling changes took place along the WE-direction axis,and anticline traps were formed.Under the nappe,the weakly deformed E-inclined slope,the Piyaman sumperimposed fault-slope anticline-typed double structure,the Sangzhu triangular-zone structure and the imbricate thrust zone were developed successively from east to west.On the section,the imbricate thrust zone is situated below the front margin of the triangular-zone structure,and they are overlapping distributed on plane.