GEOMORPHIC EVIDENCE FOR THE LATE CENOZOIC STRIKE-SLIPPING AND THRUSTING IN LONGMEN MOUNTAIN AT THE EASTERN MARGIN OF THE TIBETAN PLATEAU
GEOMORPHIC EVIDENCE FOR THE LATE CENOZOIC STRIKE-SLIPPING AND THRUSTING IN LONGMEN MOUNTAIN AT THE EASTERN MARGIN OF THE TIBETAN PLATEAU
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发表时间：
2006
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通讯作者：
Eth Zentrum
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作者：
Eth Zentrum
本文研究了青藏高原东缘龙门山活动构造的地貌证据，在汶川-茂汶断裂、北川断裂、彭关断裂、大邑断裂等断裂带上，发现了阶地错断、陡坎、断层控制的马鞍、右向百叶脊、右向河道错断、地堑、破碎带、本文利用沉积物表层下粉砂的电子自旋共振（ESR）和热释光（TL）年龄数据，计算了推覆和走滑的速率，结果表明，青藏高原边缘新生代构造缩短较小，逆冲速率小于1.1mm/a，走滑速率小于1.46mm/a，龙门山为北北东向右旋剪切带，具有广泛的走滑断裂和次级逆冲作用，滑倾比为6（1.从北西向南东，逆冲分量变小，走滑分量变大，但这并不能解释在没有大幅度缩短的情况下，边缘地形陡崖的存在，因此我们推测某些陡崖起伏是由于侵蚀卸荷和走滑的影响。通过对沉积证据、构造证据、结合地貌证据和古地磁资料，认为走滑断裂活动方向已由中生代的SSW向左旋走滑逆转为新生代的NNE向右旋走滑。
Geomorphic evidence for active tectonics in the Longmen Mountain at the eastern margin of the Tibetan Plateau has been studied in this paper.We have surveyed some typical geomorphic markers in Wenchuan-Maowen Fault,Beichuan Fault,Pengguan Fault,and Dayi Fault,including terrace offsets,scarps,fault-controlled saddles,dextral shutter ridges,dextral channel offsets,grabens,shatter belts, and pull-apart basins.Electron spin resonance(ESR) ages and thermoluminescence(TL) ages using silty sand taken from below the surface of sediments have been obtained.According to these data,we calculated the rate of thrusting and strike-slipping,and the results indicate that the Cenozoic tectonic shortening at the margin of the Tibetan Plateau is minor with the rate of thrusting smaller than 1.1mm/a and the rate of strike-slipping smaller than 1.46mm/a,and the Longmen Mountain is a zone of NNE-directed dextral shear with extensive strike-slip faulting and secondary thrusting with slip-dip ratio of 6(∶)1～1.3(∶)1.From NW to SE,the thrust component becomes smaller,but strike-slip component becomes bigger.However,this does not explain the presence of the abrupt topographic escarpment at the margin in the absence of major shortening.We thus infer that some escarpment reliefs are due to the effects of erosional unloading and strike-slipping.Based on comparison of sedimentary evidence,tectonic evidence,geomorphic evidence and paleomagnetism between the Cenozoic and Mesozoic,we believe that the direction of strike-slip faulting has been rewersed from SSW-directed sinistral strike-slip in Mesozoic to NNE-directed dextral strike-slip in the Cenozoic.