Morphostructure Formation And Evolution Of The Liu Mu Gao Fault Zone In The Northeastern Margin Of The Tibet Plateau

The Liumugao fault zone is one of the main faults of the Niushoushan-Luoshan fault zone in the northeastern margin of the Tibet Plateau,which is not only located in the northeastern most margin of the tectonic expansion of the Tibet Plateau,but also situated to the margin of the tectonic extension system of the Yinchuan basin.And its Cenozoic tectonic geomorphic evolution process,reflected the northeast-eastward expansion of the Tibet Plateau and the information of the tectonic activity of the extension system of Yinchuan Basin.This study was mainly based on the Digital Elevation Model(DEM).Through the quantitative analysis of the topographic factors of the Liumugao fault zone,combining with related tectonic analysis and geomorphological analysis,we finally invert the morphostructure evolution process of the Liumugao fault zone,which provides a concrete basis for the analysis of the eastward extension process of the Tibet Plateau.Firstly,we extract 11 rivers and drainage basins related to the Liumugao fault zone based on World-DEM data,and calculate their geomorphic indices,including river longitudinal profiles,Hack profiles,SL indices(SL),Gradient Indices(SL/K),Hypsometric integral(HI)value and other landform factors quantitatively analyze and discuss the activity of the Liumugao fault.Secondly,we analysis the structure deformation pattern of the study area,through the extraction of elevation,slope,degree of undulation,strip profile and other parameters of the study area;combining with the field structure survey,remote sensing interpretation and fault kinematic analysis.Finally,we come to the evolutionary sequence of the tectonic landscape in the study area.The main conclusions are as follows:(1)The area-elevation-integral curves of 11 water systems controlled by the Liumugao fault zone are near the ?S‘ type,and the Hack profile is prominently convex,indicating that the fault structure is strongly active and is continuously uplifted by the structure deformation.Analysis of the mean values of HI and SLK in the 11 drainage basins indicates that the difference in uplift in the south section of the fault is relatively strong.The analysis indicates that the structural activity sequence of the Liumugao fault from strong to weak is,south,middle,and north segment.(2)Combining with previous research results and detailed tectonic stress field analysis of the Liumugao fault zone,we believe that the Liumugao fault zone has undergone three stages of tectonic evolution since the Cenozoic era,ie,NE-SW extrusions in late Miocene to early renewal;NE-SE extensions of the late Pleistocene;ENE-WSW extrusions since the late Pleistocene.(3)Tectonic movements in the study area control the geomorphological evolution process in the area,ie,under the Miocene-Early Pleistocene northeast-southwestern compressional effect,the west side of the fault zone was shortened due to thrusting,and the syncline folds and higher mountains were formed.And it has laid a geomorphic pattern that is now high in the west and low in the east;the Late Pleistocene extensional fault destructed the alluvial fan gravel layer formed in the early Pleistocene,and formed the terraces at all levels in the east side of the fault zone;the fault zone has been slippery since late late Pleistocene,and the slipper movement of the main fault zone and secondary faults transform the landform to form a smooth fault surface and cause ridges and water system shift.