Geological And Geomorphic Constraints On The Spatiotemporal Evolution Of Dushanzi Anticline In The Northern Chinese Tianshan Foreland

Due to the long-range squeezing effect of the collision between the Indian plate and the Eurasian plate,the Tianshan Mountains have undergone tectonic revival since the Late Cenozoic,forming three rows of nearly east-western reverse fault-fold belts in the northern foreland basin.The Dushanzi anticline is located at the westernmost end of the third row of reverse fault-fold belts,and it is still in continuous activity today.Quantitatively defining the growth and expansion process of the Dushanzi anticline is of great significance for understanding the spatial and temporal evolution of the foreland of the orogenic belt,understanding the growth mechanism of folds,the development process of structural geomorphology and regional seismic risk assessment.The main methods for evaluating the activity of anticlines include geological methods and geomorphic methods.Geological methods include the use of the surplus area method to calculate the anticline shortening uplift rate,the use of fault-related fold quantitative geometric model combined with the seismic profile and the age of the sedimentary strata to calculate the rate of anticline activity,etc.This method can limit the absolute geological rate at a single point or profile,but the calculation results lack space coverage.The geomorphic method uses methods such as hypsometric integral,relief,steepness,and?value to extract corresponding quantitative parameters to evaluate the structural and geomorphological characteristics of the area.The spatial coverage of the calculation results of this method is good,but it is difficult to obtain the absolute geological rate directly through the geomorphic parameters.The use of a combination of geology and geomorphology can complement each other's strengths and provide a high-precision,wide-coverage assessment of tectonic activity.At present,the geological study of the Dushanzi anticline lacks the evaluation of the active rate since the late Pleistocene,and the evaluation of the uplift and lateral propagation rates.In response to this problem,this paper first took the Wusu River terraces located at the west tip of the anticline as the research object,carried out drone aerial photography,deformation analysis and terrace age determination,etc.,and calculated the shortening,uplift and the lateral propagation rate of the anticline to the west.Then,the ages and deformations of the river terraces and alluvial fans in the central and eastern anticlines were calculated,and the uplift rates in the central and eastern anticlines were calculated.Finally,based on the previous research results on the activity rate of Dushanzi anticline,the shortening,uplift and lateral propagation rates of Dushanzi anticline at different time scales in the middle,east and west were covered comprehensively.At present,the research on the geomorphology of Dushanzi anticline lacks the evaluation of the geomorphic parameters.To solve this problem,this paper calculates and interpolates the HI,k_sn,relief and?value of Dushanzi anticline based on ALOS-12.5m DEM data to obtain the spatial distribution map of each parameter.Combining the calculation results of geological rate and geomorphic parameters,this article discusses the geomorphic and structural features of Dushanzi anticline as follows:?1?Spatial distribution of anticline activity rate:a comparative analysis of the spatial distribution of geomorphic parameters and the absolute geological rate of typical locations,To precisely define the spatial distribution of the activity rate of Dushanzi anticline.?2?Evolutionary sequences of anticline tectonic landforms:compare the geomorphic characteristics and activity rates with different uplift times in different regions to explore the changes of anticline activity rates and their geomorphic responses.?3?Construction of the evolution model of Dushanzi anticline:based on the research results of the activity rate of anticline and the spatial and temporal distribution of geomorphic parameters,the spatial and temporal evolution model of the structure and geomorphology of Dushanzi anticline is constructed.The results show that the formation ages of the T3,T2,and T1 terraces of the Wusu River at the west tip of the Dushanzi anticline are 83.7_-4.5^+4.4ka?55.6_-3.2^+4.4ka and 28.4_-1.6^+2.4ka.Combining the deformation amount of the terrace,the shortening rates of the anticline from the formation ages of the T3,T2,and T1 terraces of the Wusu River are 0.63±0.03mm/a,0.84±0.06mm/a and 0.92±0.06mm/a respectively,and the uplift rates are 0.67±0.03mm/a,0.87±0.06mm/a and 1.01±0.07 mm/a.Using the spatial distribution and ages of the Wusu River terraces,a lateral propagation rate of 12.9±0.5mm/a westward from the anticline was obtained.Counting the age and deformation of Kuitun river's terrace and the alluvial fan in the eastern part of the anticline,the uplift rate of 1.89±0.27 mm/a in the central anticline from 7.5-10 ka and the uplift rate of 1.43mm/a in the eastern anticline from 30 ka were obtained.The spatial distribution of k_sn was calibrated using the uplift rate at the typical positions of the anticline,and the spatial distribution of the uplift rate of the Dushanzi anticline was obtained.The results show that from the tip of the anticline to the core of the anticline,the rate of uplift generally increases linearly.The uplift rate at the west tip of the anticline is generally?1 mm/a,and the rate increases toward the east,and the uplift rate to the Kuitun River area increases to about 2 mm/a.The east bank of the Kuitun River represents the core area of the anticline,and the uplift rate reaches the peak of the anticline uplift rate?>2 mm/a?.The rate of uplift from the core to the east gradually decreased,and the rate in the area of the alluvial fan east of the anticline decreased to about 1.43 mm/a.The rate of uplift from the east to the east boundary of the anticline gradually decreased to zero.By comparing the difference in uplift time between different regions of the anticline caused by the lateral growth of the anticline and the different geomorphic parameter characteristics of these regions,the evolution process of the k_sn,HI and relief during the anticline growth was obtained.The results show that the HI showed a downward trend during the evolution of Dushanzi anticline,corresponding to the development of the geomorphic evolution stage.k_sn showed an overall upward trend,corresponding to the acceleration process of shortening and uplift during the evolution of Dushanzi anticline.The relief showed a trend of increasing first and then decreasing,which reflects the continuous change of the surface morphology during the evolution of the anticline from the river's gradual deep cut to the later relief of the topography.Combining the three-dimensional growth rate of the anticline,the moving direction of the divide and the evolution time sequence of the geomorphic parameters,a spatial-temporal structural geomorphology evolution model of the Dushanzi anticline was constructed.The calculation result of the?value of Dushanzi anticline shows that the erosion first formed the valley of the core of the anticline and formed an annular watershed distributed along the edge of the valley.With the continuous evolution of the anticline,the watershed has a tendency to migrate from the core to the outside of the anticline.During this process,the value of k_sn as a whole is high in the core and low in the outer side.As the anticline grows,the high value area of k_sn gradually expands from the core to the outer side.The overall value of the HI index is characterized by lower in core and higher in the outer side.As the anticline grows,the range of the low HI index area gradually expands from the core to the outer side.The overall relief is characterized by lower in core and boundary and higher in the middle.As the anticline grows,the peak area in the middle gradually moves toward the anticline boundary.The highlights and innovations of this study have played a role in promoting the related structural geomorphology research.In this paper,the lateral growth rate of the anticline is calculated by the lateral migration of the river.This method has the potential to be applied in other research areas with similar geological conditions.The geomorphic parameter method is applied to the study of active anticlines,and a model of the spatial variation of geomorphic parameters during the evolution of anticlines is established.This model can be referenced in the structural geomorphological studies of the other active anticlines.In addition,the age of the river terraces in Dushanzi anticline can be applied to the scientific researches such as climate change in the North Tianshan area.The shortening,uplift and lateral propagation rates in different regions and timescales can be used in the quantitative study of regional kinematics and dynamics of the North Tianshan reverse fault-fold belt.The results of the study are of great significance for understanding the evolution process of the tectonic geomorphology of the Dushanzi anticline and the evaluation of regional activity of the anticline.