长江三峡库首区地壳表层工程地质环境演化的探讨

文章对三峡库首区的工程地质环境演化进行了较全面的探讨,尤其是对某些有争议的问题进行了论证并据自己的工作得到一些新的结果。作者首先论证了库首区的地壳表层结构,强调仙女山、九湾溪、天阳坪三断裂构成的K字型断裂系的重要意义,并据断裂构造岩的成分结构及力学性质分析了仙女山断裂的多期活动及孕震物理。其次从白垩—老第三系的分布、温泉的排列、地形变的协调性、地应力的一致性论证了仙女山断裂活动自新构造期以来即已南北一体化,其北延过江的形式是反经验的,即以挤压应力拗折带的形式过江,而在地表无确定的断裂带存在。第三,由赤平投影解,水系优势方位统计等反演研究及现代地应力测量结果,证明库首区自燕山运动以来基本上以NW向应力场为主,属于NNW向构造体系。第四,由阶地、第四纪堆积物及物理地质作用的研究,发现新滩地带不存在阶地“超覆”,瑶子“砾岩”并无明显的构造变形迹象。库首区自新构造期始至今稳定抬升,升率约为0.1 mm/gt。在此背景下,发育了秭归—渔洋关孕震断裂带及黔江—兴山孕震断裂带的一部分。这两个带控制的地区、地壳内外动力地质作用活跃。特别是新滩地带近2000年的重力崩滑(外动力)与区域地震(内动力)在时空上具有明显的相谐性。此外,文中还结合三峡的新构造研究提出了新构造期次划分方案,它对于工程地质环境研究是有实际意义的。

A Discussion on the Engineering Geology Environment Evolution of Surface Crust of the Three Gorges Project Aera of Yangtze River

This paper has carried out a complete discussion on the engineering geology eaviroament evolution of the three Gorges project area, particularly is some controversy problems. Based on the author's research work, some new results have been obtained. First, the auther expounds the surface crust structure of the Project area, emphasizing the important signifcances of the three faults of Xiannushan Fault. Jiowanxi Fault, and Tianyangping Fault and analyzing the multiperiodic activity and earthquake-pregnant mechanism of Xiannushan Fault in term of the composition, the structure and the dynamic property of the fault tectonites. Second, it slso expounds that the activity of Xiannushan Fault has been mainly in the direction of Souty and North in term of the distrubution of Cretaceous system and old Tertiary system, the position of warm springs, the topography harmony and the ground stress consistency. Third, according to the mosern ground stress results and stereographic analysing results, etc, it proves that the ground stress in the Project area has been basically in the direction of North and East Since Yanshan Mountain Movements. Fourth, Based on the study on the physical action of geology and the accumulation of Quaternary system it has also been found that there does not exist the terrace overlap, in Xiantan Aera and that Yaozi conglomerates have no tectonic deformation evidences. Moreover, combined the new structure study of the three Gorges, this paper also puts forwards a dividing plan for new tectonic period, which has some practical significances to the study of engineering geology environments.