关键词: 阿尔金断裂系, 河流水系, 河流长度坡度指数, 河流陡峭指数, 面积-高程曲线, 运动学特征

Abstract: The North Altyn fault, located between the Tibetan Plateau and the Tarim Basin, is an important boundary for the northward expansion of the Tibetan Plateau. At present, there is still of great controversy about its kinematics during the Cenozoic. In this paper, DEM data are used to extract the geomorphic information of 18 rivers and related catchment basins passing through the North Altyn fault. Geomorphic index parameters, such as river geometries in both map and section views, standardized river length slope index (SLK), standardized river steepness index (Ksn), area-elevation curves and their integrals (HIs) of catchment basins, are analyzed to study the tectonic activity of the North Altyn fault during the Late Quaternary. The results show that the longitudinal elevation profiles of the rivers and the area-elevation curves of the corresponding catchment basins along the western part of the North Altyn fault are both concave downward, with many small knickpoints on in the river profile, and relatively low SLK, Ksn, and HI values. On the contrary, most of the river profiles in the eastern part of the fault are of convex or linear shapes, with the development of large knickpoints on the hanging wall of the North Altyn fault, which coincide with high SLK and KSN values. The associated area-elevation curves are mainly S-shaped and convex, and the HI values are relatively large. The above geomorphological indicators show that the geomorphic activity of the eastern part of the North Altyn fault is stronger than that of the western part. We infer that this along-strike variation results from intense lateral contraction from the large Akato restraining double bend of the active South Altyn Tagh fault to the south of the eastern part of the North Altyn fault. No systematic sinistral dislocation has been detected on the studied rivers when they pass through the North Altyn fault. A newly discovered frontal fault folding the late Quaternary alluvial fan to the north of the North Altyn fault shows typical thrust characteristics. We thus speculate that the North Altyn fault is dominated by reverse dip-slip in the late Quaternary. Together with published results, our findings imply that the North Altyn fault likely changed from a strike-slip-dominated fault to a reverse-dominated fault, and closely interacts with the South Altyn Tagh fault in the late Cenozoic.

Key words: Altyn Tagh fault system, River system, River length slope index, River steepness index, Area-elevation curve, Kinematic characteristics