Abstract Numerical model simulations and experiments have suggested that when migration of the main drainage divide occurs in a mountain belt, it can lead to the rearrangement of river catchments, rejuvenation of topography, and changes in erosion rates and sediment flux. We assess the progressive mobility of the drainage divide in three lithologically and structurally distinct groups of bedrock in the High Atlas (NW Africa). The geological age of bedrock and its associated tectonic architecture in the mountain belt increases from east to west in the study area, allowing us to track both variations in rock strength and structural configuration which influence drainage mobility during erosion through an exhuming mountain belt. Collection of field derived measurements of rock strength using a Schmidt hammer and computer based extraction of river channel steepness permit estimations of contrasts in fluvial erodibilities of rock types. The resulting difference in fluvial erodibility between the weakest and the strongest lithological unit is up to two orders of magnitude. Published evidence of geomorphic mobility of the drainage divide indicates that such a range in erodibilities in horizontal stratigraphy of the sedimentary cover may lead to changes in erosion rates as rivers erode through strata, leading to drainage divide migration. In contrast, we show that the faulted and folded metamorphic sedimentary rocks in the centre of the mountain belt coincide with a stable drainage divide. Finally, where the strong igneous rocks of the crystalline basement are exposed after erosion of the covering meta-sediments, there is a decrease in fluvial erodibility of up to a factor of three, where the drainage divide is mobile towards the centre of the exposed crystalline basement. The mobility of the drainage divide in response to erosion through rock-types and their structural configuration in a mountain belt has implications for the perception of autogenic dynamism of drainage networks and fluvial erosion in mountain belts, and the interpretation of the geomorphology and downstream stratigraphy.

中文翻译：

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河流可蚀性的岩石强度和结构控制：对碰撞山带中排水分水岭流动性的影响

摘要 数值模型模拟和实验表明，当主要流域在山区发生迁移时，会导致河流集水区的重新排列、地形的恢复以及侵蚀速率和泥沙通量的变化。我们评估了高阿特拉斯（非洲西北部）三个岩性和结构不同的基岩组中排水分水岭的渐进流动性。在研究区，山带中基岩的地质年龄及其相关构造结构从东到西增加，这使我们能够跟踪岩石强度和结构配置的变化，这些变化影响了开挖山带侵蚀过程中的排水流动性。使用施密特锤和基于计算机的河道陡度提取收集岩石强度的现场衍生测量值，可以估计岩石类型的河流侵蚀性的对比。由此产生的最弱和最强岩性单元之间的河流可蚀性差异高达两个数量级。已发表的排水分水岭地貌移动性证据表明，沉积盖层水平地层的侵蚀性范围可能会随着河流侵蚀地层而导致侵蚀率发生变化，从而导致排水分水岭迁移。相比之下，我们表明山带中心的断层和褶皱变质沉积岩与稳定的排水分水岭重合。最后，在覆盖的变质沉积物侵蚀后，结晶基底的坚固火成岩暴露出来，河流可蚀性降低多达三倍，其中排水分水岭向暴露的结晶基底中心移动。流域分水岭响应山带中岩石类型及其结构配置的侵蚀的流动性对山带中流域网络和河流侵蚀的自生动力的感知以及地貌和下游地层的解释具有重要意义。