NEOTECTONIC SIGNIFICANCE REVEALED BY STREAM LENGTH – GRADIENT INDEX OF THE DAXI RIVER BASIN IN THE SOUTHERN MARGIN OF ORDOS, CHINA

Abstract. Since the late Cenozoic era, due to the impact of the Indo- Eurasian plate collision and the northeasterward compression of the Tibetan Plateau, a series of extensional sub-basins and tectonic belts have been formed at the periphery of the Ordos block. Watershed geomorphology plays an important role in studying the formation of rock uplift and river erosion, and are recording the surface evidence on landforms evolution. In this paper, twenty-eight sub-basins and tributaries around Daxihe River, locating at the southern margin of Ordos, were extracted from SRTM1 DEM data. Combined with Hack profile and related river parameters, the tectonic and geomorphic morphology were evaluated synthetically. The results show that (1) The mean SL of this area is 93.9, indicating that the tectonic activities are strong in Daxihe River Basin; (2) The SL values of the northern and southern are 58.9–152 and 66–137.4, respectively, showing that the uplift rate of eastern margin larger than the southern margin; (3) There are positive power functions between K and drainage area, also between landform relief and slope. This study plays an auxiliary role in regional geological background, structural activity analysis and disaster prediction.