Active tectonics of the Beichuan and Pengguan faults at the eastern margin of the Tibetan Plateau
Active tectonics of the Beichuan and Pengguan faults at the eastern margin of the Tibetan Plateau
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DOI：
10.1029/2006tc001987
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发表时间：
2007-07-17
期刊：
影响因子：
4.2
通讯作者：
Richardson, Nicholas
中科院分区：
文献类型：
--
作者：
Densmore, Alexander L.;Ellis, Michael A.;Richardson, Nicholas
青藏高原东缘陡倾、地形起伏大，新生代经历了快速的冷却和剥蚀，但没有证据表明前陆盆地发生了大幅度缩短或可容纳空间。我们解决这个矛盾，通过使用各种地貌观测的几个大的断层，平行高原边缘的运动学和滑动率的限制。北川断裂和彭官断裂是一条活动的、以右行走滑为主的断裂，沿高原边缘可连续追踪长达沿着200 km。这两个断层抵消河流充填阶地，产生遗传校正，宇宙成因10 Be暴露年龄< 15 kyr，表明最新的更新世活动。彭官断裂在全新世时似乎有两个沿着走向的活动点。两个断层的最新第四纪视落差率沿走向沿着变化，但通常小于1 mm/年（-1）。走滑位移的速率可能要高出几倍，可能与1-10毫米/年（-1）相似，但仍然受到很差的约束。晚第四纪褶皱和右行走滑也发生在沿着四川盆地西缘，特别是与现在的山前。这些观测结果支持不涉及上地壳缩短的东部高原边缘的形成和维持模型。他们还认为，西藏东部边缘平行断层的活动可能对人口稠密的四川盆地构成重大的地震危险。
The steep, high-relief eastern margin of the Tibetan Plateau has undergone rapid Cenozoic cooling and denudation yet shows little evidence for large- magnitude shortening or accommodation generation in the foreland basin. We address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin. The Beichuan and Pengguan faults are active, dominantly dextral- slip structures that can be traced continuously for up to 200 km along the plateau margin. Both faults offset fluvial fill terraces that yield inheritance- corrected, cosmogenic 10 Be exposure ages of < 15 kyr, indicating latest Pleistocene activity. The Pengguan fault appears to have been active in the Holocene at two sites along strike. Latest Quaternary apparent throw rates on both faults are variable along strike but are typically < 1 mm yr(-1). Rates of strike- slip displacement are likely to be several times higher, probably similar to 1-10 mm yr(-1) but remain poorly constrained. Late Quaternary folding and dextral strike- slip has also occurred along the western margin of the Sichuan Basin, particularly associated with the present- day mountain front. These observations support models for the formation and maintenance of the eastern plateau margin that do not involve major upper crustal shortening. They also suggest that activity on the margin- parallel faults in eastern Tibet may represent a significant seismic hazard to the densely populated Sichuan Basin.