Basement Metamorphic Rocks Deformed And Metamorphosed Characteristics. Possession Of Dongba Qingxian North

On the basis of 1:250,000 regional geological survey of the Cêgnêsheet, this paper mainly study the microfabric deformation character and the metamorphism of the basement metamorphic series exposed at north of Baqên County, eastern Tibet. Based on the field observations, we applied methods which combined microstructure with macroscopic structure, deformation with metamorphism, tectonothermal with isotope dating. The specific work includes measurements of foliations and lineations, microfabric deformation observations, strain measurement and electron microprobe analysis, etc. The conclusions we arrived at are as follows: ①the foliation and lineation of penetration developed in the basement metamorphic series of the study area. The foliations forms broad antiform and synform. Flattened the penetration foliations, the lineations is approximately NW-trending. ②According to microstructural and electron microprobe analyse, it has been determined that at least three metamorphic stages occurred in the basement metamorphic series in the region. ③The deformation mechanism of the basement metamorphic series is transversal tectono-transposition of extension regime. The result is the X-axis and Y-axis of the strain ellipsoid extended, while the Z-axis shortened. That is X>Y>1>Z. ④According to the mineral assemblage, the metamorphic facies belongs to greenschist facies —amphibolite facies. ⑤The metamorphic conditions of principal-stage: the temperature is about 400℃-600℃and its pressure is about 0.3-0.8Gp. ⑥The principal-stage deformation and metamorphism occurred at late of Indo-Chinese epoch, relating to the early stage break-up of Bangonghu-Nujiang.