Along-strike topographic variation of Qinghai Nanshan and its significance for landscape evolution in the northeastern Tibetan Plateau

摘要

Cenozoic basins and ranges constitute the high topography of the northeastern Tibetan Plateau which is derived from the Indo-Asian collision. The geomorphological characteristics of the ranges provide direct insight into the uplift processes which are responsible for the patterns of the ranges and the growth of the northeastern Tibetan Plateau. This study analyzed the geomorphological features of Qinghai Nanshan (one of the youngest ranges within the northeastern Tibetan Plateau), including elevation, slope distribution and the channel steepness index. Topographic analysis revealed that elevations and slopes in western and central portions of Qinghai Nanshan were higher than those in the eastern portion, whereas the channel steepness index revealed a step growth mode from west to east. Considering the topographic features, the lateral gradient of precipitation (increasing from west to east) and the lithology distribution, it is concluded that the geomorphological features of Qinghai Nanshan are influenced mainly by tectonic activities and reflect the growth pattern and/or the tectonic setting of the range. Comparing with previous studies, it is shown that the formation mechanism of Qinghai Nanshan follows a middle-to-sides growth pattern. Furthermore, the degree of inclination of the erosion surface distributed on the northern flank of the range suggests that Qinghai Nanshan is controlled jointly by the listric Qinghai Nanshan thrust fault and the influences from the Elashan and Riyueshan dextral strike slip faults. In addition, the northeastern Tibetan Plateau exhibits an outside-in growth process, which might reflect the northeastward growth of the entire northeastern Tibetan Plateau.