Analysis Of Late Quaternary Activity Characteristics Of The Fault Zone Along The Southern Margin Of Wuwei Basin On The Northeastern Margin Of Qilian Mountains

The fault zone along the southern margin of Wuwei basin is an important tectonic transition zone for the NE-direction expansion of the Qinghai-Tibet Plateau.Its tectonic activity as a whole reflects the interaction between the Qinghai-Tibet Plateau and the surrounding Dunhuang block,Alxa block and Ordos block.Reveals the growth and evolution process of the fault zone along the southern margin of Wuwei basin.The study of geometry,kinematics,formation and evolution of The fault zone along the southern margin of Wuwei basin is of great significance for the exploration of the growth and evolution of the northeastern margin of the Qinghai-Tibet Plateau and the evaluation of active structures.In this paper,guided by structural analysis,through remote sensing image interpretation,field geological survey,optical luminescence dating and other methods,detailed geometry,kinematics and active time limit analysis of the fault zone along the southern margin of Wuwei basin are carried out.Based on the study of fault geometry,the faults are divided into Xidahe-Dongdahe section(F1),the West of Xiying River section(F2),the East of Kangning Village section(F3),the East of Nanying River section(F4),shanggucheng village-zhangliugou section(F5),and it is considered that the fault zone along the southern margin of Wuwei basin is an active fault with thrust as the main thrust since Late Quaternary and partly with left-handed strike slip movement,from west to East,The vertical displacement and horizontal left rotation movement of the fracture zone are increasing gradually,and the deformation degree reaches the maximum in the middle section.The activity rate of the fault zone in the late Quaternary is about 0.3-0.8 mm/a,and the horizontal sliding rate is about 0.3-1.5 mm/a.At the same time,as an important tectonic transition zone between the Qinghai Tibet Plateau and the Alxa block,the fault zone is of great significance in regulating the tectonic stress balance and crustal shortening in the boundary zone of the block.Based on the study of river terraces system in the region,it is considered that 1-3 river terraces have generally occurred since Holocene,which represents at least 3 tectonic activities in the region.Based on the analysis of dating results,the first time of river cutting occurred in the early Holocene,the second time between 7000-3000 a B.P.,and the third time since 1000 a B.P.,which basically coincided with the time of fault activity mentioned above.It is considered that the stress perpendicular to Lenglongling fault in the cold Longling transition area is transmitted to the southern edge of Wuwei basin,which is the main reason for the surface fracture in the late Quaternary period.Under the hindrance of NNW and NE faults in the area,the reverse thrust and strike slip movement mode has been formed,and the present surface distribution pattern is formed.