Climatic versus tectonic control on river incision at the margin of NE Tibet: 10Be exposure dating of river terraces at the mountain front of the Qilian Shan
Climatic versus tectonic control on river incision at the margin of NE Tibet: 10Be exposure dating of river terraces at the mountain front of the Qilian Shan
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DOI：
10.1029/2005jf000352
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发表时间：
2006-09
影响因子：
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通讯作者：
R. Hetzel;S. Niedermann;Mingxin Tao;P. Kubik;M. Strecker
中科院分区：
文献类型：
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作者：
R. Hetzel;S. Niedermann;Mingxin Tao;P. Kubik;M. Strecker
[1]我们的文件晚更新世-全新世加积和切割过程中的祁连山，一个活跃的陆内褶皱和冲断带，容纳了印度-亚洲会聚的重要部分的山前。石油河穿过北北东向的逆断层传播褶皱，核心为中新世红层，北方前缘为上新世-第四纪生长地层。在背斜以南，中新世地层倾向20 ° SSW，表明基底滑脱的方向相似。石油河沉积了150 m厚的晚更新世河谷充填物，形成了三个阶地。最高的阶地位于河上170米处，构成了填土的顶部。其他的梯田是填挖梯田：它们的台阶分别位于河上130 - 105米和37米处。阶地的10Be暴露测年表明，在10 - 15 kyr时，河流的切割速度从0.8 ± 0.2 mm yr − 1加速到100 mm yr − 1。我们解释快速全新世河流切割在很大程度上无关的构造强迫。晚更新世的下切速率为0.8 ± 0.2 mm/年，水平缩短速率的上限为2.2 ± 0.5 mm/年，假设下切仅由倾斜20 °的滑脱层上方的岩石抬升引起。然而，实际的缩短速率可能介于0.22mm/年和零之间，因为阶地和山谷填充的变形无法明确证明。我们的估计与新构造和GPS数据得出的西藏东北部几个断层的整体缩短率为10.5 - 10 mm/年一致，尽管在石油河的情况下，由于强烈的气候引起的河流切割，全新世变形几乎不可辨别。
[1] We document late Pleistocene–Holocene aggradation and incision processes at the mountain front of the Qilian Shan, an active intracontinental fold-and-thrust belt accommodating a significant portion of the India-Asia convergence. The Shiyou River cuts through a NNE vergent fault propagation fold with Miocene red beds in the core and Pliocene–Quaternary growth strata on the northern forelimb. South of the anticline, Miocene strata dip 20° SSW, suggesting a similar orientation for the basal decollement. After aggradation of an ∼150-m-thick, late Pleistocene valley fill, the Shiyou River formed three terraces. The highest terrace, located 170 m above the river, constitutes the top of the fill. The other terraces are fill cut terraces: their treads are located 130–105 m and 37 m above the river, respectively. The 10Be exposure dating of the terraces suggests that river incision accelerated from 0.8 ± 0.2 mm yr−1 to ∼10 mm yr−1 at 10–15 kyr. We interpret fast Holocene river incision as largely unrelated to tectonic forcing. The late Pleistocene incision rate of 0.8 ± 0.2 mm yr−1 places an upper limit of 2.2 ± 0.5 mm yr−1 on the horizontal shortening rate, assuming that incision is solely caused by rock uplift above a decollement dipping 20°. However, the actual shortening rate may lie between ∼2.2 mm yr−1 and zero because deformation of the terraces and the valley fill cannot be unequivocally demonstrated. Our estimate is consistent with the bulk shortening rate of ∼5–10 mm yr−1 across several faults in NE Tibet derived from neotectonic and GPS data, although in case of the Shiyou River, Holocene deformation is barely discernible owing to intense climate-induced river incision.