Late Quaternary Activity And Tectonic Transition Of The Sinistral Slip Faults,Eastern Tian Shan

The research on the deformation pattern and evolution process in one of the hot topics in earth science field.As an intracontinental orogenic belt which lies far away from plate boundary,the Tian Shan has entense tectonic deformation,complex deformation patterns and frequent seismic activities.The Cenozoic deformation of the Tianshan Mountains is mainly characterized by compression and shortening,and the deformation is mainly accommodated and absorbed by the piedmont-thrust fold belt and large strike-slip faults.GPS observations have shown that crustal shortening across the eastern Tian Shan is ～20 mm/yr,and the N-S shortening rates gradually decrease eastward to 3～5 mm/yr in eastern Tian Shan.The remarkable difference in shortening rates may indicate the deformation patterns between west and east Tian Shan is different.The present research on the Cenozoic tectonic deformation is mainly focused on the west Tian Shan,however,the research on the late Quaternary deformation feature of faults in east Tian Shan is very lacking.Obtained the Altai mountains in the north,the east even the Gobi Altai,give priority to with extrusion shortening deformation in west Tian Shan tectonic system,Altai NW to dextral tectonic system and the Gobi Altai nearly EW left spin structure system conversion of the intersection area,therefore,the study of fracture tectonic deformation in the lower can not only provide quantitative parameters for seismic hazard assessment in the area,It is helpful to understand the deformation framework and the deformation model of the eastern Tianshan Mountains.Based on the study of the deformation of the main fault structures in the East Tianshan Mountains,the following understandings have been obtained:1.The Baoertu fault is a large deep fault that divides the central Tianshan block from the southern Tianshan block.It trends nearly EW and have a total length of about 300 km.The fault has been characterized by sinistral strike-slip movement with a certain thrust component since the late Quaternary.The lateral slip rate of 0.7± 0.2mm /yr and the vertical slip rate of 0.05± 0.01 mm /yr after 110 ka were obtained by displacement recovery of the gouge or the fan edge that was broken along the fault.The differential eastward slip of the central Tian Shan block and the Yanqi-Kumish block bounded by Baoertu fault,Boa fault and Kaidu fault is the main reason driving the left-lateral movement of the Baoertu fault.2.The Karlik Tagh north fault is located at the easternmost end of Tianshan Mountain,which is arc-shaped between Karlik Mountain and Yiwu Basin.According to the change of fault strike and movement property,the fault can be divided into two parts.The western segment is NW strike and is characterized by thrust slip,and the vertical slip rate is 0.08 mm/yr since the late Pleistocene.The eastern segment is NE-NEE trending,which is mainly sinistral strike-slip and has some thrust component.It connects with the Gobi-Tianshan sinistral strike-slip fault system in the east,southwest of Mongolia.According to the displacement of the Xiamaya river terraces and the exposure age of the terraces,the left-lateral sliding rate of the eastern section of the fault is 1.1-1.3mm /yr since 180 ka.3.The Jianquanzi-Barkol fault and the northern margin fault of Hami Basin are two important faults at the eastern end of the East Tian Shan.The Jianquanzi-Barkol fault starts from the southeastern margin of Bogda Mountain and spreads eastward along the northern margin of Barkol Tagh.In the south of the Tuolaiquan Basin,the sinistral strike-slip rate is 2.6±0.2 mm/yr obtained by measuring the displacement of gullies and the dating of diluvial fan,which is similar to the fault slip rate defined by previous authors in the Xiongkur fault zone.The eastern segment of the fault shows a NW strike and extends in the piedmont.The minimum shortening rate of east segment since the Late Pleistocene is 0.13～0.22 mm/yr.The fault migrates to the interior of the basin to form the Kuisu anticline,and the shortening rate since the end of the Middle Pleistocene is 0.45 mm/yr.The fault in the northern margin of Hami Basin is distributed between Balikun Tagh and Karlik Tagh in Hami Basin.The thrust deformation is the main feature since the late Quaternary.The vertical slip rate of the fault is 0.07～0.12 mm/yr since 190 ka,and the fault activity is continuous in time without significant change.4.By summarizing the geometric and kinematic characteristics of the late Cenozoic active faults in the East Tian Shan,we conclude that the main feature of western segment of the East Tian Shan is compression shortening deformation and the shortening rate of ～ 4.67mm/yr is absorbed by all structures across the Tian Shan,which is consistent with the shortening rate defined by GPS method.The eastern section of the eastern Tianshan Mountains is generally transformed into a compressional tectonic ramework.The western segment of Jianquanzi-Barkol fault and the eastern segment of the northern margin fault of Karlik Tagh are arranged in the right order on the plane,and a compressional order zone is formed between the faults.From west to east,the sinistral strike-slip rate of the Jianquanzi-Balikun fault was absorbed by the thrust fault in the step region and then transferred eastward to the eastern part of the Northern Karlik Tagh fault or to the sinistral strike-slip system of the Gobi Tian Shan.5.Due to remote effect of the collision between the Indian plate and the Eurasian plate,the Tian Shan are pushed laterally to the east and west by the northward Tarim Basin.In the western part of the east Tian Shan,the Baoertu fault acts as the boundary fault between blocks,which regulates the differential slip between blocks within the Tian Shan.In the eastern section of the eastern Tian Shan,the sinistral strike-slip fault plays a controlling role in the regional deformation,which transmits the deformation eastward to the southern region of Mongolia.6.Barkol Tagh and Karlik Tagh can be characterized by sinistral compressional orogenic belt,and the mountain is located at the compression step zone of strike-slip faults.Their uplift is controlled by both the piedmont thrust faults and the strike-slip faults,and gradually extends outward through the migration of the piedmont thrust faults to the basin on both the north and south sides.