Understanding erosion rates in the Himalayan orogen: A case study from the Arun Valley
Understanding erosion rates in the Himalayan orogen: A case study from the Arun Valley
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DOI：
10.1002/2014jf003410
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发表时间：
2015-10
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通讯作者：
Stephanie Olen;B. Bookhagen;B. Hoffmann;D. Sachse;D. P. Adhikari;M. Strecker
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文献类型：
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作者：
Stephanie Olen;B. Bookhagen;B. Hoffmann;D. Sachse;D. P. Adhikari;M. Strecker
了解侵蚀的速度和模式是破译气候和构造对景观演变影响的关键方面。从陆地宇宙成因核素得出的剥蚀率通常用于量化侵蚀和连接构造(MyR)和气候(长达几千年)的时间尺度。然而，活动造山带的侵蚀过程如何最终反映在10Be TCN样品中仍然是一个讨论的话题。我们在尼泊尔东部的阿伦山谷用34个新的10Be导出的集水区平均剥蚀率来研究这个问题。阿伦山谷的特点是地形和气候的南北梯度陡峭。在局部上，剥蚀速率向北增加，支流样品的剥蚀率从0.2mmyr−1增加到~1.5mmyr−1，而主干样品似乎从西藏边界的~0.2mmyr−1向下游增加到前陆的0.91mmyr−1。剥蚀率与归一化河道陡度最相关(R2=0.67)，后者通常被解释为指示构造活动。主干Arun中下游10Be浓度的显著下降表明，上游沉积物颗粒正在细化，以至于在操作上将它们排除在处理样品之外。这导致10Be浓度和剥蚀率不能统一代表上游集水区。我们观察到局部非河流地貌过程对10Be浓度的强烈影响，如冰川作用和滑坡与降雨率峰值地区重合，表明主要受构造驱动的剥蚀速率的气候调制。
Understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution. Denudation rates derived from terrestrial cosmogenic nuclides (TCNs) are commonly used to quantify erosion and bridge tectonic (Myr) and climatic (up to several kiloyears) time scales. However, how the processes of erosion in active orogens are ultimately reflected in 10Be TCN samples remains a topic of discussion. We investigate this problem in the Arun Valley of eastern Nepal with 34 new 10Be‐derived catchment‐mean denudation rates. The Arun Valley is characterized by steep north‐south gradients in topography and climate. Locally, denudation rates increase northward, from <0.2 mm yr−1 to ~1.5 mm yr−1 in tributary samples, while main stem samples appear to increase downstream from ~0.2 mm yr−1 at the border with Tibet to 0.91 mm yr−1 in the foreland. Denudation rates most strongly correlate with normalized channel steepness (R2 = 0.67), which has been commonly interpreted to indicate tectonic activity. Significant downstream decrease of 10Be concentration in the main stem Arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample. This results in 10Be concentrations and denudation rates that do not uniformly represent the upstream catchment area. We observe strong impacts on 10Be concentrations from local, nonfluvial geomorphic processes, such as glaciation and landsliding coinciding with areas of peak rainfall rates, pointing toward climatic modulation of predominantly tectonically driven denudation rates.