Late Quaternaryactive Characteristics Of The Southern Riyueshan Fault

Due to the collision between the Indian plate and the Asia-Europe plate,the Tibetan Plateau experienced a violent uplift and formed a strong deformation within the plate,which had a huge impact on the tectonic activities,basin evolution,and environmental changes in the surrounding area.Regarding the structural deformation model of the Tibetan Plateau,there are mainly end-member processes:plate-like rigid-body motion and distributed deformation via viscous flow.The biggest contradiction between the two models is whether there are thousands of kilometers of giant strike-slip faults in the northern Tibetan Plateau as the boundaries of rigid blocks,and whether there are high-speed inter-plate activities.To solve this problem,a more in-depth study on the characteristics of fault activity is needed,and a more detailed quantitative study of active structural parameters is needed.The northeast edge of the Tibetan Plateau is the forefront of the north-east expansion of the Tibetan Plateau,and is the best place to understand the expansion of the plateau.There are two main groups of faults controlling the evolution of the geomorphology in this area:a group of sinistral strike-slip faults with nearly east-west trending,such as the East Kunlun fault and the Haiyuan fault,are the main block boundary faults;The study of large sinistral faults on the boundary of the body has been more in-depth;the other group is north-north-westward dextral strike-slip faults,such as the Elashan fault and the Riyueshan fault.Among them,dextral faults such as Elashan fault and Riyueshan fault bear the amount of shear of the internal rotation of the block.The research on the Riyueshan fault is currently mainly concentrated in the northern section,and the research on the southern section is very sparse.There is little research about the fault characteristics such as the distribution style,active age,and activity of the late Quaternary in the southern section.Therefore,this paper chooses the southern section of the Riyueshan fault as the study area to supplement the active structural parameters of the northern section of the Riyueshan fault.The paper is based on the field investigation of the southern section of the Riyueshan fault,high-precision remote sensing images,and interpretation of typical dislocation point UAV photogrammetry images,etc.to obtain its fine geometric distribution,combined with OSL,14C and other dating methods to obtain chronology.Based on the data,the slip rate and dislocation distribution characteristics since the Holocene have been determined,and the role of the fault in the structural deformation of the northeastern margin of the Tibetan Plateau has been discussed.The main conclusions obtained in the thesis are as follows:(1)There are traces of Holocene activities in the southern section of the Riyueshan fault.Risers,gullies,dextral dislocations,faulty ponds,linear ridges and other characteristics,and scraps can be observed in research areas such as Rixiaolongwa and Niemari.Ridges,,these fault features all surface that the southern segment of the Riyueshan fault is a Holocene active fault.(2)The southern section of Riyueshan fault can be divided into two sections from the strike,surface fracture and bedrock outcrop:the Guide section and the Duohemao section.There are many fault branches in the Guide section,and the fault strike is more complicated.The main fault features are fault gullies,risers,fault ponds,and fault ridges.The Duohemao section has a nearly NW direction.The secondary faults are characterized by the obvious development of linear ridges and linear ridges.Among them,the Guide section and the Duohemao section can be divided into three sub-sections.(3)We accurately determined the Late Quaternary slip rate in the southern section of the Riyueshan Fault,obtained high-resolution DEM using drone photogrammetry technology,and measured the faulty geomorphic landmarks using LaDiCaoz_v2 software;14C and light were used.Luminescence dating technology has obtained the age series of different terraces at 7 points.Monte Carlo simulation algorithm is used to calculate the slip rate of different points.The slip rate of the southern section of the Riyueshan fault is2.03-0.27+0.32 mm/yr,3.37-0.68+0.55mm/yr,2.53-0.39+0.42 mm/yr,2.69-0.38+0.41 mm/yr,1.58-0.18+0.21 mm/yr,2.13-1.19+1.15mm/yr,1.94-0.33+0.32mm/yr.(4)Based on previous studies,the role of the Riyueshan fault in the deformation of the northeastern margin of the Qinghai-Tibet Plateau is comprehensively discussed.It is believed that the Riyueshan fault and the Elashan fault are a set of dually developed faults.Eastward flattening to jointly absorb the shortening of the crust,and the rate results support the "non-rigid book oblique structure model".