中文摘要：

柴迭木盆地北缘大柴旦地区超高压变质岩的围岩——长英质片麻岩的主要矿物组合为石榴子石＋蓝晶石＋多硅白云母＋条纹长石＋石英＋斜长石，形成压力在800MPav；t上。在阴极发光图像内部结构研究的基础上，利用LA-ICP-MS对该长英质片麻岩中锆石的变质微区进行了详细的原位微区U—Pb定年，得到206^Pb/238^U加权平均年龄为427．2Ma±4．5Ma，对应的Th/U为0．01～0．06。该年龄与本区已有的榴辉岩的围岩超高压泥质片麻岩、石榴子石橄榄岩的变质年龄在误差范围内一致。

英文摘要：

The main mineral assemblage of quartzo-feldspathic gneisses--the country rocks of ultrahigh-pressure （UHP） metamorphic rocks in the Da Qaidam area on the northern margin of the Qaidam basin is garnet ＋ kyanite ＋ phengite ＋ perthite ＋quartz ＋ plagioclase, which suggests that this rock formed at least at 800 MPa. Based on a study of the internal structure of ce （CL） images, LA-ICP-MS U-Pb dating was carried out ＂on the zircons from the quartzo-feldspathic gneisses. Analyses of 22 spots in the metamorphic area in the zircons yield a 206^Pb/236^U weighted average age of 427.2±4.5 Ma with a corresponding Th/U ratio of 0.01 to 0.06. This age is within error consistent with the peak metamorphic ages of the country rocks of eclogite--UHP pelitic gneisses and garnet peridotite--in this area.