Folded fluvial terraces in a young, actively deforming intramontane basin between the Yumu Shan and the Qilian Shan mountains, NE Tibet
Folded fluvial terraces in a young, actively deforming intramontane basin between the Yumu Shan and the Qilian Shan mountains, NE Tibet
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西藏东北部玉木山和祁连山之间年轻、变形活跃的山内盆地中的褶皱河流阶地
DOI：
10.1130/l614.1
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发表时间：
2017
期刊：
影响因子：
2.4
通讯作者：
Geng Haopeng
中科院分区：
文献类型：
--
作者：
Hu Xiaofei;Pan Baotian;Fan Yuxin;Wang Jun;Hu Zhenbo;Cao Bo;Li Qingyang;Geng Haopeng
活跃变形区的山内盆地包含造山带演化的重要信息。我们利用大河沿岸河流阶地的变形来约束整个盆地第四纪变形的速率和模式。河流地貌包括广泛分布的中更新世冲积-河流扇面和五个阶地。我们通过对风成黄土和河流沉积物的光激发发光（OSL）分析，确定了与这些地貌相关的沉积物的年代。我们的结果得出142.8±11.3 ka (Fs), 103-125 ka (T5), 96-115 ka (T4), 87-104 ka （T3）和13-15 ka （T2）的年龄，我们认为这反映了河流阶地表面的放弃。高程测量表明，阶地表面沿大河背斜褶皱，沿盆地向北缓慢倾斜。阶地变形分析表明，大河背斜以翼缘旋转方式发育，并以0.14 +0.14/ -0.03 mm/a的速率适应上地壳缩短。根据背斜南翼的旋转速率，我们确定变形发生在0.3 ~ 0.9 Ma之间。这一年龄明显小于祁连山逆冲断层（约10 Ma）和玉木山逆冲断层（约3.7 Ma）的起裂年龄。阶地变形特征表明，大河背斜是由南倾滑脱发育而成的，这也引起了整个盆地的地表倾斜。晚第四纪大河背斜褶皱的活化和拆离滑动表明，山内盆地的变形发生时间远晚于周围山脉，并通过盆地变窄容纳了部分地壳缩短。
Intramontane basins in actively deforming regions contain significant information about the evolution of orogenic belts. We explored the tectonic characteristics and evolution of an intramontane basin between the Qilian Shan and Yumu Shan mountains on the NE Tibetan Plateau. We utilized the deformation of fluvial terraces along the Dahe River to constrain the rate and pattern of Quaternary deformation across the basin. Fluvial landforms include a widespread Mid-Pleistocene alluvial-fluvial fan surface and five terrace levels inset below this surface. We dated deposits associated with these landforms by optically stimulated luminescence (OSL) analyses on eolian loess and fluvial sediments. Our results yield ages of 142.8 ± 11.3 ka (Fs), 103–125 ka (T5), 96–115 ka (T4), 87–104 ka (T3), and 13–15 ka (T2), which we interpret to reflect the abandonment of fluvial terrace surfaces. Elevation surveys indicate that the terrace surfaces are folded along the Dahe anticline and are gently tilted northward across the basin. Analysis of terrace deformation suggests that the Dahe anticline grew by limb rotation and accommodated upper-crustal shortening at a rate of 0.14 +0.14/–0.03 mm/a. We determined the onset of deformation to have occurred between 0.3 and 0.9 Ma, based on the rotation rate of the southern limb of the anticline. This age is significantly younger than the onset ages of the thrust faults along the Qilian Shan (ca. 10 Ma) and the Yumu Shan (ca. 3.7 Ma). The character of the terrace deformation suggests that the Dahe anticline was growing from a south-dipping decollement, which also induced surface tilting across the entire basin. The Late Quaternary activation of the Dahe anticline folding and the detachment slipping provide evidence that the deformation of the intramontane basin occurred much later than that of the surrounding mountain ranges and accommodated part of the crustal shortening through basin narrowing.