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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, Nd isotopic composition of five whole-rock samples called “khondalites” in the core of the Huangling anticline was determined. Five samples represent the different layers and lithologies of the rock series, respectively. ΕCe (t) of two dark-plagioclase gneisses containing graphite and one garnet-bearing quartzite schist samples are negative (-2.5, -2.1 and -1.7, respectively), εNd (t ) Values are relatively high (-0.5, -1,3, and -1,6, respectively), revealing that the rock contains more mantle-derived components and that the original rock depositional environment is not stable. The εCe of a garnet sillimanite schist The value of εNd (t) is -2.4, indicating that the sedimentary environment of the original rock accords with the geological conditions for forming khondalites. All features of the black cloud granulite are similar to those of the gneiss, εCe ( t) and εNd (t) values are +2 2 and -7 7, respectively. The Nd model age is 3169 ± 19 Ma, indicating that it may not belong to the Paleoproterozoic. In conclusion, the Paleoproterozoic sedimentary tectonic setting in the Huangling area is not all stable. There are obvious activities of the seafloor mantle source components at the beginning and intermediate stages of the sedimentation of the rock series. Therefore, the sedimentary- The tectonic environment exists only for some time, and some strata may belong to the Archean.