Distribution of active rock uplift along the eastern margin of the Tibetan Plateau: Inferences from bedrock channel longitudinal profiles
Distribution of active rock uplift along the eastern margin of the Tibetan Plateau: Inferences from bedrock channel longitudinal profiles
复制标题
DOI：
10.1029/2001jb000861
复制
发表时间：
2003-04
影响因子：
--
通讯作者：
E. Kirby;K. Whipple;W. Tang;Zhiliang Chen
中科院分区：
文献类型：
--
作者：
E. Kirby;K. Whipple;W. Tang;Zhiliang Chen
[1]现有的河流切入基岩的长期模型表明，局部岩石差异抬升速率应对河道纵断面的坡度起主要控制作用。然而，事实证明，将这种影响与基质腐蚀性、沉积物通量、降水和剖面形状的瞬时变化的影响区分开来已被证明是困难的。在此，我们研究了四川盆地附近基岩河道坡度空间分布的控制，试图评估青藏高原边缘活动变形的程度和性质。利用河道陡度指数(流域面积归一化的剖面坡度测量)对河流纵向剖面进行分析，发现高原边缘地形前缘附近有一条异常陡峭的河道带。在高原上的源头河段和高原边缘以东的下游，河道剖面总体上不那么陡峭。陡度指数与绘制的岩性变化对比表明，岩性对该区河道坡度的影响有限。我们没有观察到陡度指数与上游流域面积之间的系统关系；在高原边缘附近，各种大小的河道都比较陡峭。我们认为，这些系统性的变化并不容易解释为泥沙通量增加或地形降水的结果。结果表明，高原地形前缘陡峭的河道剖面反映了该地区与前陆之间活跃的差异岩石隆升。
[1] Current models of long-term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles. However, discrimination of this effect from the influence of variations in substrate erodibility, sediment flux, precipitation, and transient changes in profile shape has proved difficult in practice. Here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the Sichuan Basin in an effort to assess the degree and nature of active deformation along this margin of the Tibetan Plateau. Analysis of river longitudinal profiles utilizing a channel steepness index (a measure of profile gradient normalized for drainage area) reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin. Channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin. Comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area. We observe no systematic relationship between steepness indices and upstream drainage area; channels of all size are steeper near the plateau margin. We argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation. We are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland.