四川省区域地质概况及特征

四川的地层发育齐全,从上太古界到第四系均有。全省具双层结构特点的前震旦系基底。在晚震旦世一三叠纪,四川东、西部地区地质发展迥然不同,东部地区进入地台发展阶段。而西部仍处于地槽活动状态。变质岩主要分布在西部及东部的西边缘。东部仅有前震旦系变质,而西部三叠系以下地层均已变质。晋宁、印支、喜马拉雅运动是四川重要的构造运动。全省可分为四个一级大地构造单元:杨子准地台、松潘—甘孜褶皱系、三江褶皱系和秦岭褶皱系。杨子准地台自震旦纪开始进入地台发展阶段,松潘—甘孜褶皱系与三江褶皱系经历两次地槽发展阶段。

A GENERAL ACCOUNT OF THE REGIONAL GEOLOGY OFSICHUAN PROVINCE

A complete sequence of strata is developed in Sichuan, including those from the upper Archean to the Quaternary. The pre-Sinian System in the whole province is characterized by a two-layered structure. In the late Sinian to Triassic, the geological development was utterly different in the eastern and western parts of Sichuan. The eastern part entered the stage of platform development, while the western part was still in the stage of geosynclinal activity. The metamorphic rocks are mainly distribcted in the western part and on the western margin part. In the western part, the Triassic rocks and those below them have all been metamorphosed, while in the eastern part only the pre-Sinian rocks have been metamorphosed. Metamorp hism is dominated by regional tow-temperatcre dynamic metamorphism and migmatization took place in the terminal Zhongtiaoian and terminal variscan periods. The Jinning, Indosinian and Himalayan movements are important tectonic movements in Sichuan. In the whole province four firstorder tectonic units may be distinguished: the Yangtze paraplatform, Songpan-Garzefold system, Sanjiang fold systemand Qinling fold system. The Yangtze paraplatform started to enter the stage of platform development in the Sinian and the Songpan-Garze and Sanjiang fold systems had undergone two stages of geosynclinal development.