黄河中游晋陕峡谷的DEM流域特征分析及其新构造意义

DEM DRAINAGE ANALYSIS OF THE SHANXI-SHAANXI GORGE IN THE MIDDLE REACHES OF THE HUANGHE RIVER AND ITS NEOTECTONIC IMPLICATIONS

晋陕峡谷以南北走向穿越鄂尔多斯高原东缘,形成黄土高原上独特的峡谷地貌。本文基于数字高程模型,结合野外调查,提取了峡谷区的一系列相关流域地貌特征参数,详细分析了晋陕峡谷内流域特征。研究结果表明峡谷流域内水系和亚盆地表现出显著的东西分异特征,峡谷西侧水系和亚盆地的发育相对于其东侧较为成熟。其成因分析反映晚新生代以来,鄂尔多斯高原东缘可能存在多期强烈构造差异隆升事件,吕梁山相对于鄂尔多斯高原发生多期快速隆升,三门古湖消亡,导致峡谷内黄河强烈的不均匀下切,水系和亚盆地发育发生东西分异。晋陕峡谷的形成主要是晚新生代以来青藏高原发生多期向东快速构造挤出,导致鄂尔多斯高原东缘发生差异构造隆升的结果。

The S-N oriented Shanxi-Shaanxi Gorge crosses the east margin of the Ordos Plateau where the river systems and sub-basins are characterized by an asymmetric E-W -oriented form. Based on Digital Elevation Model（DEM）, combing with field observation, this paper analyzed some typical parameters of the drainage development, such as the area,the shape index, the maximum channel length, the maximum channel drop, the network density, and the channel ramification ratio of the Shanxi-Shaanxi Gorge. The result shows that river systems and sub-basins developed in the Shanxi-Shaanxi Gorge is marked by an asymmetric E-W - oriented form. For example,the sub- basins（ area 〉 5000km^2 ）are all developed in the west the west flank is 1314.55km^2 ,far bigger than in the flank of the gorge, and the average area size of sub-basins in east. Similarly, compared with that in the west flank, shape index of sub-basins in the west flank is usually much greater. In addition, maximum channel length in the west flank is 200km,much longer than in the east. Likewise,network density of sub-basins in the west flank is at least 10. Contrarily,maximum channel drop in the east flank is 100m at least,markedly bigger than in the west. In the same way, channel ramification ratio of sub-basins in the west flank is much bigger than in the east. The differences of river system developed in the Shanxi-shaanxi Gorge may imply that river systems and sub-basins in the west of the Ordos Plateau might have more developed than those in the east which is likely caused by neotectonic differences. Causing analysis indicates that because of the existence of several episodes of different uplifts in the flanks of the Ordos Plateau during the Late Cenozoic, Ltiliang Mountains uplift more rapidly than the Ordos Plateau and the Sanmen Lake disappeared, resulting in the strong incising of rivers here and the asymmetrical E-W - oriented development of sub-basins. The formation of the Shanxi-Shaanxi Gorge might have been related mainly to episodic fast eastward tectonic extrusion of the Qinghai-Tibetan Plateau and to the differential vertical uplift in the east margin of the Ordos Plateau during the Late Cenozoic. Features of tectonic morphology of the Shanxi-Shaanxi Gorge can be used to reveal the development history of the Huanghe Rvier. They can also provide quantified geological information for the study of uplift of the east margin of the Ordos Plateau since Late Cenozoic.