Cenozoic Deformation And Evolution Of The West Part Of The Southern Depression In The Junggar Basin, Xinjiang, China

The western section of the Southern Margin of Junggar Basin(SMJB)is an intersection area of the Tianshan Mountain,Chepaizi uplift,Sikeshu depression,and Shawan depression.The Aika fault,the Hongche fault,and the South Anjihai-South Manasi fault formed in Mesozoic at the western section of the SMJB.An arc of uplift developed along these strike-slip faults.The west of the uplift is the Sikeshu depression,and the east is the Shawan depression.The tectonic framework of two depressions and one uplift was formed in Mesozoic at the western section of the SMJB.The Cenozoic thrust structure occurred in the Mesozoic tectonic setting and developed different deformation at the Chepaizi uplift,the Sikeshu depression,and the Shawan depression,respectively.?Structural analysis shows that two phases of Mesozoic and Cenozoic deformation have taken place in the Sikeshu depression.The Cenozoic structural wedge formed in the Piedmont of Mountain,and the Mesozoic folds and faults are exposed to the top of the structural wedge,higher than 7000 m relative the Mesozoic layer in the basin,uplifted by folding and faulting of the wedge since the Lower Miocene.The Cenozoic echelon folds developed along the Aika strike-slip fault which was a Mesozoic fault.?The N-S trend Chepaizi uplift is perpendicular to the E-W trend the Mountain.It is difficult that the thrust faults of the Mountain extend to the Chepaizi uplift.The back thrusts developed underneath the piedmont of Mountain that caused the South Anjihai-South Manasi fold belt exposed along the Mountain.?Two rows of parallel folds,including Huoerguosi anticline,Manas-Tugulu anticline,and Anjihai anticline developed in the Shawan depression.These stacked folds consisted of the detachment folds in the deep layer,having a detachment fault in the Jurassic Xishanyao Formation coal bed,and fault-propagation folds in the shallow layer,thrusting in the Eogene Aijihaihe Formation mudstone.The main tectonic deformation in the Piedmont of the Tianshan Mountain started in lower Miocene Era(15-20Ma)and migrated gradually from the Mountain to the foreland basin of Junggar,with the faulting and folding becoming younger and weakened in the basin.The folds in the foreland basin formed in Pliocene(3Ma).