A Study On The Neotectonic Movement Of The Qianshan Fault In The Northern Segment Of The Longmen Mountains And The Evolution Of The Lancang River System

Based on the research results of the neotectonic movement in the northern section of longmen shan fault piedmont zone,combined with the fujiang river alluvial fan optically stimulated luminescence(OSL)dating data,the response relationship of the fujiang river drainage system evolution and active faults in the northern section of longmen shan fault piedmont were studied.(1)Fujiang river alluvial fan development characteristics and datingThe study area on the regional structure is make of Jiangyou fault ?huanglianqiao fault?tongkou fault and xiangshui—rangshui fault and so on composition Jiangyou fault zone,It belongs to the dextral strike-slip tectonic domain.The strike of these fault roughly parallel with the strike of the northern section of longmenshan fault zone.Jiang you fault zone is an important part of the active faults in the northern section of longmenshan fault zone.Jiangyou right-lateral strike-slip faults to the tectonic geomorphic-fujiang river allluvial fan control effect is remarkable.There are not of uniform size,Irregular shape and from Northeast to southwest distribution of fujiang river allluvial fan in the northern section of longmenshan fault piedmont zone.The elevation difference of between the Early pleistocene fujiang river alluvial fan and the middle pleistocene fujiang river alluvial fan is 50 meters;the elevation difference of between the Early pleistocene fujiang river alluvial fan and The holocene fujiang river alluvial fan is 100 meters.Influenced by right-lateral strike-slip activity of jiangyou fracture,the development of lateral superposed of fujiang river alluvial fan.Through field sampling,Indoor Optically Stimulated Luminescence(OSL)dating tests,the result shows that from northeasten to southwesten,respectively,the Early pleistocene fujiang river alluvial fan,its Optically Stimulated Luminescence(OSL)dating result is 1.73~1.84Ma;the middle pleistocene fujiang river alluvial fan,its Optically Stimulated Luminescence(OSL)dating result is 0.54Ma;Until the end of the holocene fujiang river alluvial fan.(2)The study of right-lateral strike-slip rate of Jiangyou fractureThe distance of between the early pleistocene fujiang river alluvial fan fan top and the middle Pleistocene fujiang river alluvial fan fan top is 3.2 km;The distance of between the early pleistocene fujiang river alluvial fan fan top and The holocene fujiang river alluvial fan fan top is4 km.Through above fujiang river ancient alluvial fan Optically Stimulated Luminescence(OSL)dating to know: The forming times of the middle pleistocene age of Fujiang river alluvial fan is0.54Ma;The forming times of the early pleistocene age of Fujiang river alluvial fan is1.73~1.84 Ma.On the basis of the above data we can calculate that: Since 0.54 Ma,dextral strike-slip fault rate of jiangyou fault is 1.48 mm/a;Since 1.84 Ma,dextral strike-slip fault rate of jiangyou fault is 2.17 mm/a;Since the holocene,jiangyou fracture has been basically stopped activity.Its shows that since the Pleistocene Jiangyou fracture of activity weakened,Until the basically stop activity.since the early Pleistocene,Jiangyou faults were right-lateral strike-slip fault twice.(3)Fujiang river water system evolution the response process of active faultsBefore the early pleistocene,the northern section of longmenshan foreland basin has formed.According to the early pleistocene fujiang river ancient alluvial fan gravel flat bearing estimate:After fujiang river out of longmen mountain,River flow from the N to the S direction shift from the N to the NNW direction.At this time,after speculate that the ancient fujiang river through the town of yongsheng,the ancient Fu river and the ancient Zi Tong river confluence.The period of the Early Pleistocene,Longmenshan fold uplift,Jiangyou fracture were strong right-lateral strike-slip activities,The ancient fujiang river is dextral diversionsed by jiangyou fracture in the front of the longmen mountain.According to the early pleistocene fujiang river ancient alluvial fan gravel flat bearing estimate: After fujiang river out of longmen mountain,The ancient fujiang river flow from the NNW direction of the early Pleistocene to NW direction.And according to the above measurement,The distance of between the early pleistocene fujiang river alluvial fan fan top and the middle Pleistocene fujiang river alluvial fan fan top is 3.2 km.After the Middle Pleistocene,Longmen mountains continue to fold uplift,although Jiangyou fracture were still right-lateral strike-slip activities,but the strength of the activity has been weaked.The ancient fujiang river diversions once again.During the holocene epoch,Jiangyou fracture has been largely discontinued,after the fujiang river channel changed,the channel basically remain unchanged.