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.