藏北羌塘中部高压变质带中石榴子石白云母片岩的岩石学和变质特征

羌塘中部的高压变质带位于龙木错-双湖-澜沧江板块缝合带之上，由榴辉岩、蓝片岩和石榴子石白云母片岩组成，其形成过程对探讨板块缝合带的构造演化具有重要意义。以其中的石榴子石白云母片岩为研究对象，通过岩相学研究并结合电子探针成分分析，认为石榴子石白云母片岩中的石榴子石具有多期次变质结晶的特征，保留了岩石多期次变质的信息。结合岩石组构特征，最终确定石榴子石白云母片岩至少经历了3期次的变质作用。第一、二期均为绿片岩相，当时岩石不具定向构造且未达到高压；第三期为低温高压蓝片岩相变质作用，与区域上蓝片岩的形成及榴辉岩的蓝片岩相退变质作用大体同时，该期变质变形作用形成了岩石的片理，最终成为石榴子石白云母片岩，变质作用时代为218Ma左右。

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.