阿尔金山东段河道陡峭指数对区域隆升差异的响应

THE RESPONSE OF THE CHANNEL STEEPNESS INDEX TO THE DIFFERENCE OF UPLIFT RATE IN THE EASTERN SECTION OF ALTYN MOUNTAINS

阿尔金山东段是青藏高原北部边界带的重要组成部分，其构造活动特征及隆升信息是研究青藏高原隆升机制的重要内容。随着地貌学的深入研究，河道陡峭指数作为一种地貌参数可以对区域构造隆升有较好反映。本文提取了阿尔金山东段地区自西向东5个亚区域（A、13、C、D和E）的16条河道陡峭指数剖面，并利用数理统计学方法对其进行统计分析，揭示该区域的构造活动特征。研究表明，这5个亚区域区内的河道陡峭指数均值分别为70．93、139．03、108．85、134．44和165．39，整体表现出河道陡峭指数从西到东逐渐增大趋势；通过对区内地层、降雨量及河道负载程度、基岩隆升等因素的分析，认为区内河道陡峭指数主要受到基岩隆升影响，而上述其他因素影响有限。各亚区域间河道陡峭指数的变化反映了区域内隆升活动性的差异性：阿尔金山东段隆升活动性整体为北高南低、东高西低特征，山脉北部主要承接来自青藏高原内部挤压应力，而东西方向上存在阿尔金构造带与祁连构造带衔接部位，断层性质由近东西向水平走滑逐渐转换为北东向的挤压逆冲，存在明显应力调整与转换。

The eastern section of Altyn Mountains is an important part of the Ahyn orogenic belt in the Qinghai-Tibet Plateau. The study on the uplift rate and the distribution feature in this region provides important clues for understanding the uplift mechanism of Qinghai-Tibet Plateau. As an important geomorphic unit in the land, fluvial system records there levant between tectonics and climate. In recent years, the study for the Channel steepness index （ksn） conducted by many researchers using the geomorphology model of equilibrium channel longitudinal profiles, combines bedrock uplift and river incision, making it possible to extract rock uplift history from river profiles. The results of the study： regional rock uplift rate is the main factor in affecting the Channel steepness index. Other factors, such as climate, lithostratigraphy, rainfall and so on, make little difference. And there is a response relationship between the Channel steepness index and the uplift rate. This relationship can be used to evaluate the regional activity and the intensity of tectonic uplift.In this paper, the ASTER GDEM, spatial resolution of 30m, was utilized as basic data, and combined the ArcGIS and MATLABL software to extract the channel steepness index from equilibrium channel longitudinal profiles model. At the same time, we used statistical methods to analyze the channel steepness index. Our results show that the Channel steepness index of the eastern section of Ahyn Mountains from west to east A, B, C, D and E five segments are respectively 70.93, 139.03,108.85, 134.44 and 165.39 in average. We find that the change of the Channel steepness index reflects the distribution pattern of structure uplift rate in different region. At first, the Channel steepness index gradually increases from west to east, and it also reflects the regional uplift rate information. The uplift rate of the western section is slowest and is mainly characterized by strike slip motion, while the eastern part is the fastest and its motion is dominated by thrust, showing a strong activity. Secondly, the results appear north section high south low, east high west low phenomenon. This is mainly caused by the north boundary zone of the Altyn orogenic belt endured compressive stress from the inside of Qinghai-Tibet Plateau, and the eastern is the stress transition zone. It is worth mentioned that our results consistent with previous studies on the active characteristics of the eastern section of the Altyn Tagh Fault.