Analysis Of Structural Deformation Characteristics Of Xiaowan Area In The Northeast Margin Of Dunhuang Block

The Dunhuang Block is located in the eastern margin of the Tarim Block,adjacent to the Alxa Block in the east,and the Kuruteg Block in the northwest,which has important tectonic significance.This on the basis of predecessors' research results based on the Gansu province Anxi Area,A large number of field geological surveys have been carried out in Xiaowan Area on the northeast margin of Dunhuang Block,A systematic study was conducted on the structural deformation characteristics,focusing on the formation mechanism of structural deformation in nanshan area of Xiaowan,and the geological evolution process from early proterozoic to Meso-Cenozoic was discussed.The following aspects were obtained:(1)the relative deformation sequence was established and the structural deformation of the five phases was determined.They are: high plastic deformation structures in the first dunhuang rock group.The second stage is the permeable structure in dunhuang rock group,Cambrian rock mass and sedimentary volcanic rock.The third stage is the ductile deformation characteristics of dunhuang rocks.The fourth and fifth stages are Cenozoic faults.(2)according to zircon u-pb dating,the first phase deformation was formed between 0.89 and 1.15 Ga,and the second phase deformation was formed between0.41 and 0.48 Ga.The third deformation period was late Paleozoic.The deformation time of the fourth and fifth phases was later than 164 Ma.(3)the first stage deformation combination is the gnetting,gnetting,kneading fold,enteric fold and deep-dissolved fold developed in Dunhuang rock group.Deformation of the second phase of the combination of dunhuang closed drape and left shear properties of rocks cuhk gut suture line structure,the Cambrian sedimentary-giant compound synclinal volcanic rock and secondary fold,the Cambrian ductile shear zone in the rock mass,the Cambrian sedimentary-the green schist facies metamorphic volcanic rock and fold covering for bedding,ordovician and siluriangneissic structure of rock mass and granulite facies metamorphism;The third deformation assemblage is e-w or nww-see thrust ductile shear zone and left-lateral shear zone fold in Cambrian sediment-volcanic rocks,and e-w left-lateral thrust fault.The fourth phase deformation combination was nnw-sse/nww-see shear fault to the right.The fifth stage deformation combination is nne-ssw/nee-sww left-lateral strike-slip thrust shear fault.(4)the first phase deformation occurred in the northern margin of aljin and the southern margin of dunhuang block in the neoproterozoic tectonic heat event,which experienced the convergence and disintegration of the Rodinia supercontinent.Phase ii and iii deformation is probably related to the collision between the tarim craton and the southern margin of the central Asian orogenic belt.The third phase of deformation may be involved in the orogenic events in the central Asian orogenic belt,just like the tianshan-beishan orogenic belt.The fourth and fifth stages of the altun fault experienced the early-middle yanshanian fault and the paleogene-neogene Himalayan movement.