鄂西黄陵地区“孔兹岩”的Ce、Nd同位素特征  

Ce,Nd ISOTOPIC CHARACTERISTICS OF THE "KHONGALITE" FROM HUANGLING AREA,WESTERN HUBEI

作　　者：李志昌[1] 肖志发[1] 刘文贵[1] 

机构地区：[1]宜昌地质矿产研究所,宜昌443003

出　　处：《华南地质与矿产》2001年第2期8-12,共5页Geology and Mineral Resources of South China

基　　金：原地质矿产部地质行业科技发展基金 (95 96 11)资助。

摘　　要：测定了黄陵背斜核部被称作“孔兹岩系”的 5个全岩样品Ce、Nd同位素组成 ,5个样品分别代表该岩系不同层位与岩性。其中两个含有石墨的黑云斜长片麻岩和一个含榴黑云石英片岩样品的εCe(t)都是负值 (分别为 - 2 5、- 2 1和 - 1 7) ,εNd(t)值相对高 (分别为 - 0 5、- 1 3和- 1 6) ,揭示了岩石中含有较多幔源组分 ,原岩沉积环境不稳定 ;一个石榴石矽线石石英片岩的εCe(t)值为 +1 6,εNd(t)值是 - 2 4 ,指示原岩的沉积环境符合形成孔兹岩的地质条件 ;黑云变粒岩的所有特征与基底片麻岩相似 ,εCe(t)和εNd(t)值分别为 +2 2和 - 7 7,Nd模式年龄为 (3169± 19)Ma ,表明它可能不属于古元古代。总之 ,黄陵地区古元古代的沉积构造环境并不全是稳定的 ,在岩系沉积开始阶段和中间某个时期有明显的海底幔源组分活动 ,因此 ,符合孔兹岩形成条件的沉积 -构造环境只在其中一段时间里存在 ,另外有一些地层可能属于太古宙。The Ce and Nd isotopic components of five whole rock samples of khongalite from the Huangling area of western Hubei province are reported. Two samples of graphite bearing biotite plagioclase gneiss and one sample of garnet bearing biotite quartz schist have negative ε ce ( t ) values ( -2.5 , -2.1, -1.7) and low negative ε Nd ( t ) values (-0.5, -1.3, -1.6), showing much mantle derive components included in these rocks; A sample of garnet sillimanite quartz schist has a positive ε ce ( t ) value (+1.6) and higher negative ε Nd ( t ) value(-2.4), suggesting a relative stable sedimentary setting of its primary rocks; A sample of biotite granulite has similar Ce and Nd isotopic components to those of the basement gneiss in this area with ε ce ( t )=+2.2, ε Nd ( t )=-7.7 and Nd model age of (3169±19) Ma. So, the so called 'khongalite' in this area might include proto proterozoic Al rich metasedimentary rocks and Archean basement gneiss.

关 键 词：钕同位素 沉积环境 片麻岩 铈同位素 变质沉积岩 孔兹岩 

分 类 号：P588.2[天文地球—岩石学]