李琼,
秦冰雪,
潘保田
兰州大学资源环境学院, 西部环境教育部重点实验室, 甘肃 兰州 730000

基金项目: 国家自然科学基金项目（批准号：41771002、41201004和41730637）和中央高校基本科研业务费专项项目（批准号：lzujbky-2016-160）共同资助


详细信息

作者简介: 李琼, 女, 40岁, 高级实验师, 河流地貌学研究, E-mail:qli@lzu.edu.cn

中图分类号: P931.2;P542

收稿日期:2019-05-11
修回日期:2019-08-30
刊出日期:2020-01-25

Bedrock channel width responses to tectonic uplift and lithologic resistance in the northern Qilian Mountains

Li Qiong,
Qin Bingxue,
Pan Baotian
Key Laboratory of Western China's Environment Systems(Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, Gansu



MSC: P931.2;P542

--> Received Date: 11 May 2019
Revised Date: 30 August 2019
Publish Date: 25 January 2020


摘要
摘要:活动造山带基岩河流地貌研究，目前已成为构造地貌学研究的前沿和热点。河道宽度形态的调整变化是基岩河流响应构造、岩性和气候等扰动的重要方式之一。通过研究祁连山北部地区6个重点流域基岩河道的宽度形态发现：河道宽度总体上呈现出东西向和南北向的变化特征，河道向下游增宽的速率，东段地区显著高于中段地区，低山带显著高于高山带；对比河道宽度的变化特征与构造抬升速率及岩性抗蚀性的变化，可以推断：在祁连山北部地区，基岩河道宽度响应构造抬升和岩性抗蚀性的变化进行了系统地调整，构造抬升控制了流域河道宽度变化的总体趋势，而岩性抗蚀性变化则导致了流域内部局部河段河道宽度的大幅波动。在祁连山北部地区开展的基岩河道宽度形态研究，为利用基岩河道形态研究造山带的构造变形奠定了基础，对于探索构造抬升背景下地貌的发育过程具有十分重要的意义。
关键词: 基岩河流/
河道宽度/
构造抬升/
岩性/
祁连山

Abstract:Increasing recognition that cross-section shape serves as an adjustable primary feature of both alluvial and bedrock rivers has refined traditional views that changes in channel slope dominate fluvial response to variable tectonic, climate, and lithologic conditions. Downstream adjustment of channel width is an important way that rivers response to external forcing such as varying rock uplift rates, bedrock erodibility and so on.
In this paper, we analyze downstream changes in channel width of six rivers draining the northern Qilian Mountains in an effort to explore how bedrock rivers adjust their channel width in response to lithologic resistance and tectonic uplift.
Our study area is located in the northern Qilian Mountains where topographic relief exhibits a pronounced stepwise distribution. From the south to the north it can be divided into three different topographic zones (tectonic uplift zones):the high mountain zone or high uplift rate zone (HMZ/HUZ, 3500~5000 m), the low mountain zone or low uplift rate zone (LMZ/LUZ, 2500~3200 m) and the corridor plain zone (CPZ, 1500 m). Our study area experiences intensive erosion and rock uplift during Quaternary, which are caused by the activities of the major thrust fault systems trending NWW. Moreover, bedrock resistance is different between the topographic zones due to the various underlying strata. Therefore, the northern Qilian Mountains is an ideal area for bedrock channel morphology study. Our study is conducted mainly around six large bedrock rivers including the Beida, Fengle, Liyuan, Xiying, Jinta and Zamu rivers from the west to the east, in which the west three belong to the Hei drainage and the east three to the Shiyang drainage. In this field survey, a total group of ca. 300 high-flow channel width and ca. 160 bedrock outcrops strength data are collected along the Beida, Fengle, Liyuan and Zamu rivers utilizing a laser rangefinder and a Schmidt hammer (N type), respectively. In addition, in previous field survey in the eastern Qilian Mountains, we had collected a total of ca. 640 high-flow channel width and ca. 170 bedrock outcrops strength data along the Xiying and Jinta rivers. All of the drainage characteristic parameters such as contribute area, gradient, longitudinal profile are extracted from digital topographic data (SRTM, 90 m) base on the ArcGIS 10.0 and Matlab 2016 a.
Our results suggest that the downstream adjustments of channel width in the northern Qilian Mountains exhibit a distinct regularity along the east-west and north-south directions. Firstly, the downstream increasing of channel width for the channels draining in the eastern section are more rapid than the channels draining in the middle section and the width-area index b' are 0.40 and 0.27, respectively; the LMZ channels are more rapid than the HMZ channels, and the values of b' are 0.43 and 0.35, respectively. In addition, downstream adjustments of channel width for the six survey rivers, three follow the classical hydraulic geometry relationship (Liyuan, Xiying and Jinta) and however, three contradict it in apparent (Beida, Fengle and Zamu).
Comparing spatial distribution patterns of lithologic strength and differential tectonic uplift rates (estimating by steepness index k_sn) with channel width adjustments along each of the individual rivers indicates that:(1) The systematic adjustments of channel width in the northern Qilian Mountains mainly response to the differential rock uplift controlled by the major NWW-trending thrust faults; (2) The influence of lithologic resistance on channel width is limited to the local reaches in the individual drainage instead dominating the whole area. In general, tectonic uplift and lithologic variation, to a different extent, have an important influence on bedrock channel width. Channel width adjustment is an important way that bedrock river response to external tectonic forcing and local lithologic resistance variation in the northern Qilian Mountains.
Key words:bedrock river/
channel width/
tectonic uplift/
lithologic resistance/
Qilian Mountains



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