长江三峡复杂斜坡成因问题

On the evolution of complex slopes in the Three Gorges of Changjiang River

三峡库区涉及移民工程规划建设的滑坡研究与防治已有近20年的历史,但三峡主库区尤其是巴东、巫山和奉节等地的滑坡地质成因问题仍没有解决。作者基于多年的地质考察与研究,采用"复合堆积体"概念描述三峡库区的复杂斜坡,它是基岩、古垮塌体、古崩滑体、现代崩滑体和第四纪沉积体等几种或全部的组合体。通过研究"复合堆积体"分布的区域地质构造位置、滑坡空间分布、滑坡活动的时间分期和古崩滑体与古长江的关系,认为古川江和古峡江在奉节瞿塘峡约于45×104a～60×104a间实现两江东西贯通。形成统一的长江是一个重大自然地质事件,两江贯通导致分水岭顶部切蚀、溯源侵蚀和地下暗河或岩溶洞穴垮塌等三种地质作用异常强烈,是三峡江段大型复杂斜坡成生的主因,出现了一个复杂斜坡剧烈塑造期———形成"复合堆积体"。三峡工程建设与运行是一个新的重大人为地质事件,将使三峡水库岸坡进入一个剧烈再造期,"复合堆积体"的工程地质性质应引起工程界和学术界密切关注。最后,介绍了长江三峡河谷演化研究状况和长江形成的区域地球动力学背景。

It has been nearly twenty years that landslides were researched and controlled which related to migration engineering in the Three Gorges Reservoir of Changjiang River, but it is still not clear in the geologic causation of the complex slopes at Badong, Wushan and Fengjie counties et al. A new concept 'compound accumulation bodies' is put forward to describe the above slopes based on the author's geological exploration and study of more than ten years. The 'compound accumulation bodies' are made of bedrocks, ancient collapses and breakdowns, old and modern landslides and sediments in the Quaternary period. It is a great natural event that ancient Chuan River was connected with Xia River at Qutang Gorge between Fengjie and Wushan counties to form an unified the Yangtze River in 0.45～0.60 Ma B.P., which is obtained from the study on the regional tectonic framework, spatial distribution of landslides, division of landslide active period and position relation between ancient landslide and old river bed. The unified Changjiang River is principal factor to sculpture complex slopes, forming 'compound accumulation bodies', because it resulted in three strong geological actions, i.e. undercutting of watershed top, headwaters erosion and collapse of underground river or karst cave. The Three Gorges project construction is a new tremendous man-made event which will lead to strong changes of natural state of the 'compound accumulation bodies' for a long time. So, engineers and scientists have to pay great attention to the deformation trend of the 'compound accumulation bodies' when water level changing from 145m to 175m in the Three Gorges Reservoir. Finally, a brief study history is introduced about the Three Gorges valley development and the regional geodynamics.