Geomorphic Features Of The Greater Khingan Mountains-Taihang Mountains And Its Tectonic Implications

In recent years,the coupled structure surface climate system has been widely concerned by geologists.This research interest has also continued to increase with the development of new technologies and theories,such as cosmogenic nuclide chronology and digital elevation model.Rivers and their basins are the most basic components of the geomorphic system,and are also the most sensitive units to the tectonic climate interaction.Their morphology,development and evolution record the information of tectonic movements or climate changes at different scales in the region.The study of river water system and the analysis of watershed geomorphic characteristics are important contents in the study of tectonic geomorphology.The process of surface erosion is an important way for geomorphology to respond to the changes of various geological processes.Analyzing the amplitude and distribution of surface erosion can provide important insights for understanding the tectonic process or climate change.In order to obtain the spatial distribution characteristics of the surface erosion rate in the Greater Khingan Mountains and Taihang Mountains,and to discuss the relationship between the erosion rate and the lithological characteristics of tectonic activities,the average erosion rate of the basins in the Greater Khingan Mountains and Taihang Mountains at 10²-10⁵ time scales in different spaces was obtained by measuring the concentration of modern river sediment cosmogenic nucleogen ¹⁰Be in 12 basins in Greater Khingan Mountains and 20 basins in the Taihang Mountains.The erosion rate in the Greater Khingan Mountains is range from 8.48±0.56 mm/kyr to 17.41±1.25 mm/kyr,which is equivalent to that in other tectonic stable areas in the world,effectively ruling out the possibility of recent active tectonic movement in this area.The average erosion rate in Taihang mountain is 67.57±7.22 mm/kyr,which is about 5 times of that in Greater Khingan Mountains,and is equivalent to that of Daqing Mountain,an active fault block mountain in the northern margin of Ordos.Finally,the correlation analysis between various factors and erosion rate shows that topographic variables such as channel steepness index,local topographic relief and slope are the dominant factors controlling the surface erosion rate,while climate and lithology have little effect on the erosion rate.Drainage basins are fundamental elements of the earth’s surface,and quantifying their geomorphic features is essential to understand the interaction between tectonics,climatic,and surface processes.In this study,40 basins of the Greater Khingan Mountains were selected for hypsometric analysis using a 90-m Shuttle Radar Topography Mission digital elevation model.The hypsometric integral values range from 0.13 to 0.44,with an average value of 0.30,and most hypsometric curves exhibit remarkable downward concave shapes.This feature indicates that most drainage basins and the landscape of the Greater Khingan Mountains are approaching the old-age development stage,consistent with the present moderately stable tectonic activity.The spatial distribution of theχvalues is characterized by unambiguously higher values on the western flank than those on the eastern flank in the middle and southern segments of the Greater Khingan Mountains.We interpret this as an indicator of the disequilibrium across the main divide.The interpolation of the erosion rates and channel steepness for the catchments on both sides of the Greater Khingan Mountains revealed westward divide migration,which is consistent with the lowerχvalues,a higher slope,and local relief observed along the eastern flanks.Considering the long-term tectonic evolution pattern between the Greater Khingan Mountains and Songliao Basin,the landscape decay and slow westward divide migration were mostly driven by the inherited Cenozoic tectonics and precipitation gradient across East Asia.Taihang Mountain is located in the middle of the North China plate.It is an important geomorphic unit of the North China plate.Since the Cenozoic,it has been under the dual control of the subduction structure of the eastern Pacific plate and the collision structure of the Western Indo European continent.Its neotectonic movement is quite active.Most of the existing studies on the tectonic uplift of Taihang Mountain since the Cenozoic have used a river terrace or a thermochronological section to discuss the mountain uplift.The location is limited and is not representative.Therefore,through the inversion of longitudinal sections of 12 rivers flowing through Taihang Mountain,the tectonic evolution history of Taihang mountain area since the late Cenozoic has been restored:the accelerated relative uplift in Taihang mountain area is divided into two episodes,the first episode of uplift began at 10.2±0.6 Ma,and the relative uplift rate since 10.2 Ma is 0.09±0.003 mm/yr;The second uplift started at 4.5±0.3 Ma,and the average relative uplift rate since 4.5 Ma was 0.13±0.005 mm/yr.