Petrological characteristic and metamorphism of garnet-muscovite schist in central Qiangtang, northern Tibet, China

The central Qiangtang high pressure metamorphic belt, consisting of eclogite, glaucophane schist and garnet-muscovite schist, is located in Longmucuo-Shuanghu-Lancang river plate suture zone. Its forming process has great significance for discussing on tectonic evolution of the plate suture zone. In this paper, the garnet-muscovite schist is taken as the research object. According to the study on its petrography and electron microprobe analysis, it is proved that the garnet in garnet-muscovite schist, showing multi-stages metamorphism, saw multi-stages metamorphic crystallization. Data above, together with petrofabric characteristics, at least three metamorphic stages of garnet-muscovite schist have been distinguished. The first and second are greenschist facies. The rock has no directional structure, which indicats not reaching high pressure metamorphic condition. The schistosity and garnet-muscovite schist finally formed in the peak metamorphic stage of glaucophane schist facies(~218Ma). Moreover, accompanying with retro-metamorphism of eclogite to glaucophane schist facies, the regional glaucophane schist formed.