柴达木盆地北缘超高压变质岩的围岩长英质片麻岩锆石LA-ICP-MS定年  

LA-ICP-MS zircon U-Pb dating of quartzo-feldspathic gneisses-the country rocks of ultrahigh-pressure metamorphic rocks on the northern margin of the Qaidam basin, Northwest China.

作　　者：马旭东[1] 陈丹玲[1] 

机构地区：[1]西北大学大陆动力学教育部重点实验室西北大学地质学系,陕西西安710069

出　　处：《地质通报》2006年第1期99-103,共5页Geological Bulletin of China

基　　金：国家自然科学基金项目(编号40472043);国家重点基础研究发展规划项目(编号G1999075508);西北大学国家基础学科人才培养基地地质学创新基金(编号XDCX03-06)联合资助。

摘　　要：柴达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800MPa以上。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206Pb/238U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。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.

关 键 词：柴达木盆地北缘 长英质片麻岩 LA—ICP—MS U—Pb定年 锆石 

分 类 号：P588.345[天文地球—岩石学] P597.3[天文地球—地质学]