Study On Late Cenozoic Geomorphic Processes Of Typical Regions Along The Eastern And Northeastern Tibetan Margins

In recent years, researches on plateau uplift and orogenic evolvement focused on the evidence of surfacial process. All the studies have been becoming semi-quantitive and quantitive. And the key target of these studies is the carrier, i.e. landform, which recorded the crustal deformation and climate changes during geological time. In addition, the river drainage patterns and their implications for the plateau uplift and climate changing also have attracted more and more attentions than ever. Meanwhile, spatial analysis and applications of digital elevation model (DEM) were widely utilized in quantitive geomorphological researches, such as topographic analysis, paleosurface reconstruction and incision (erosion) analysis.Cenozoic India-Asia collision makes the higher and inboard flat Tibetan Plateau. But unlike the northern and southern margins, the eastern and northeastern ones are very disperse and irregular. Based on the discussions on different geomorphic characteristics between the eastern and northeastern margins, the Minjiang drainage basin (east Tibetan Plateau) and the Guide-Xunhua Basins (northeast Tibetan Plateau) are focused for this study. According to the extraction and processing of correlative geomorphic parameters (such as subbasin area, perimeter, channel length and bifurcation ratio) and longitudinal profile within the Minjiang drainage basin, and Pleistocene paleosurface reconstruction and incision pattern analysis, this paper draws the following ultimate conclusions:(1) Obviously different geomorphic features are determined between eastern and northeastern plateau margins. In eastern margin, the Longmenshan-Minshan tectonic belt and Sichuan Basin together build up the typical escarpment and higher slope and relief within these orogens are also remarkable. And elevation profiles across the orogenic ranges indicate shorter wavelength and higher frequency of the elevation variability. Comparably, the geomorphic features of northeastern margin show lower slope and relief, and longer wavelength and lower altitude changing frequency. Cenozoic basins widely dominate this geomorphic unit.(2) Typical drainage parameters determined within the Minjiang drainage basinare indicative for the different late Cenozoic tectonic activities between two flanks of the Minjiang River, and implying the differential late Cenozoic uplift history between two plates of the Minjiang Fault. The contrary geomorphic characteristics of eastern subbasins and western ones result from quick uplift of the Minshan and inner Longmenshan. Additionally, the macroscale regular variety and microscale anomaly of local relief within the Minjiang drainage basin are indicating the continuous increasing fluvial potential energy resulted from Minshan and Longmenshan uplift versus the Sichuan Basin, and delivering and discharging of sedimentation within local basins that build low relief landform.(3) Based on the Pleistocene paleosurface reconstruction and incision history analysis, some key techniques and methods are well documented and summarized, and correlative processing procedures are constructed.(4) According to the analysis on paleosurface, macroscale landform pattern (such as basin and range distribution) and microscale typical area (such as Huangshuihe river channel change) are analyzed and discussed, especially the studies on Huangshuihe river channel change and river incision provide new insights for the uplift and growth history of the northeastern margin of the Tibetan Plateau. Channel change of the Huangshuihe river might be indicative of the late Pleistocene uplift of the Qilian ranges. And this paper also comes to some cognition of lower uplift rate within Guide-Xunhua Basin comparing with the inner plateau.