The Geomorphy Characteristic Of Qilian Mountains And Its Response To Tibetan Plateau Uplift

Late Cenozoic upward and outward growth of the Tibetan Plateau was resulted from post-collision convergence between the Indian and Eurasian plates. Uplift and landscape evolution of the Qilian Mountains in north Tibetan Plateau was continuously fed by the upward and outward growth of the Tibetan Plateau since the collision. Qilian Mountains, tectonically belonging to the Qilian Mountains fold system in the Qinling-Qilian-Kunlun orogenic belt, has several great strike slip faults and overthrust faults. These great strike-slip faults as the Altyn Tagh fault, the Haiyuan-Qilian fault and the East Kunlun fault are important boundary fault of the Qilian Mountains, and control its landscape evolution. Based on velocity field constrained by GPS measurements, the study area generally occurs deformation, displacement vector decreases gradually from south to north. However, the motion component increases gradually from west to east, direction is clockwise rotation, turned to southeast direction until the East Qilian Mountains.Landform recordes the tectonic activities especially the new tectonic movement. The Qilian Mountains landscape features as the research object, the macro topography and fluvial geomorphology as the main research content, using the digital elevation model as the basis of the data source, with the method of digital terrain analysis, this paper discussed the geomorphy evolution of Qilian Mountains and its response to Tibetan Plateau Uplift.1) These mountains in Qilian Mountains have the characteristics of orientation and nearly equidistant. The distance is about 60 km between Qaidam Mountain, Tuergendaban Mountain, Danghenan Mountain, Shulenan Mountain, Tuolainan Mountain. Nevertheless, it shortenes to 30 km at the northeast edge of Qilian Mountains.2) The slope spectrum is defined by a statistic graph or a mathematical model, in which, the X-axis(independent variable) denotes the numerical values of a particular slope factor and the Y-axis(dependent variable) represents the corresponding area on the ground. It reflects macro spatial distribution rules of different landforms by micro topographical factors. In this study, DEM was utilized as basic data to extract the slope, aspect, slope variability(SOS), and aspect variability(SOA) from Qilian Mountains, then conducted the statistics results of the areas to rendered the slope spectrum curves. The results indicate that steep slope and abrupt slope are the major slope types, occupy 50%. 54.57% of aspects are northward, southwestward, southward, northeastward. Although the slope is steep, but the slope variability is slow. The slope spectrum image reveals landform differences between west and east of Qilian.3) Swath profile is one of the important means of quantitative landscape analysis. Compared to the terrain profile directly accessed to elevation under profile line, Swath profile is obtained with statistical information under swath extended from line. In this paper, by using the improved swath profile method, 7 Regular swath profiles were extracted. Irregular swath profile tool was developed and then used to get geomorphy characteristics. Analysis results show landform differences between west and east of Qilian, and support the view of the mountains nearly equidistant. The maximum value curve represents the surface presented in Shule Nanshan features in both axial sides of lower and the formation of a surface. The maximum value curve indicates that summit plane center around Shulenan Mountain and down to both sides.4) The peaks average elevation reflects the average gravity erosion. It is 4036 m in Qilian Mountains.There are more than 50% of peaks higher than the average value, gravity erosion is the main erosion type. The peaks average elevation obeys normal distribution. The elevation decreases from Hala Lake. Qilian Mountains likes dome, sandwiched between the Qaidam and Alashan crustal block, as a squeezed state.5) In the landscape pattern in Qilian Mountains, there is a boundary through the Hala Lake south side and parallel to the Altyn Tagh fault. In the west of the line, parallel ridge and valley is the main landform, basin is the main landscape type in the east side. The landscape pattern relates to the Altyn Tagh fault, the Haiyuan fault, the East Kunlun fault.6) River geomorphology analysis results showed that river basin development degree reduce from south to north. Qilian Mountains constructed regionaly and phasesed at different tectonic center in different period. With uplift of Tibetan Plateau, the northeastern margin of this Plateau continues to expand, make the tectonic center continuously moved northward.7) Watershed boundary is the highest edge in a basin, contains rich topographic feature information. Pass gap after river capture and fault could be distinguished from watershed boundary elevation profile.In general, the landscape pattern of Qilian Mountains is based on the original landscape, constructed by Late Cenozoic upward and outward growth of the Tibetan Plateau. Tectonic and tectonic inheritance played different roles. The tectonic center is different in different periods. The active tectonic zone is located in the northern margin of Qilian Mountains, to indicate that the Tibetan Plateau is continuous growth northeastward.