Analysis of the undating metamorphics in West Yunnan and determination of its age

On the basis of the study on its association, metamorphism, deformation, composition of debris and isotope geochronology, it indicates that West Yunnan undating metamorphics belongs to tectonic rock sheets of quite different two periods,the Middle Proterozoic Chongshan Group and the Permian Jidonglong Formation ,respectively,both of which are the dominant components of the Himalayan mixtite belt.One regional dynamothermal metamorphism took place in Chongshan Group during Upper Proterozoic Subera （727-956Ma） , and another metamorphism superimposed it during Caleodonia period （397Ma）, compared with superimposed metamorphisms in Jidonglong Formation during Himalayan period （32Ma）.