PRELIMINARY ANALYSIS ON THE DEVELOPMENT CHARACTERISTICS OF RIVER TERRACES AND THEIR RELATIONSHIP WITH ANCIENT LANDSLIDES IN THE UPPER REACHES OF MINJIANG RIVER
河流阶地形成演化及其对滑坡的控制是近年来古滑坡研究的热点问题。笔者在对岷江上游河流阶地和古滑坡实地调查测试的基础上,对岷江上游河流阶地的级序、拔河高度、成因类型等进行了分析,绘制了阶地高程位相图和年龄位相图,并结合阶地和古滑坡年代,讨论了阶地与古滑坡的发育关系等。主要取得了以下认识:1)岷江上游的河流阶地具有分段性,成因主要为气候多期次波动与构造活动共同作用,古滑坡及堰塞湖是影响高山峡谷区河流阶地发育的重要因素;2)叠溪-茂县段在20~30 kaB.P.发生了多处大型古滑坡,其中20kaB.P.的古滑坡可能主要是气候波动引发,30 ka B.P.发生的古滑坡可能主要受控于构造活动(地震);3)岷江上游大量分布的古滑坡堆积体与阶地发育的叠置关系有待进一步理清,开展该地区的河流阶地级序研究要充分考虑古滑坡和堰塞湖的影响。
英文摘要:
The upper reaches of the Minjiang River, which is located in Sichuan Province, is characterized by the development of the topographic steep zone of the Longmen Mountains, where the river terraces are developed, earthquakes occur frequently, and the landslides are numerous, widely distributed and seriously harmful, therefore, which caused widespread concern. The evolution and formation of river terraces and their control of landslides are hot issues in the field of ancient landslides study in recent years. On the basis of field investigation and comprehensive study of the river terraces and ancient landslides in the area, the sequences of the river terraces,the height of a terrace over river bed,and the genetic type of terraces in the upper reaches of the Minjiang River are analyzed by authors, the elevation and the chronological phases diagram are built, and the developmental relationship between terraces and ancient landslides was discussed. Then have achieved the following conclusions: (1) The distribution characteristics of river terraces in the upper reaches of the Minjiang River are segmental,and the genesis is mainly the multiphase climatic change fluctuations and tectonic activities. The ancient landslides and their dammed lakes are important factors for the development of river terraces in the mountain-canyon region. (2)There are many large-scale ancient landslides occurred at the 20~30ka B.P. in the Diexi-Maoxian section. Of them, the ancient landslide occurred at 20 ka B.P. may be mainly induced by climatic change fluctuations and the ancient landslides occurred at 30 ka B.P. may be mainly controlled by tectonic activities (earthquakes). (3) The overlapping relationship between the ancient landslides and the river terraces in the upper reaches of the Minjiang River needs to be further clarified, and the river terrace sequences in the region should fully consider the influence of ancient landslides mass.