五台山区变质岩系的稀土元素分布特征

稀土元素(钇及镧系)做为一组地质指示剂,国外已广泛用于矿物学及岩石学的研究。随着测试技术及分析精度的提高,国内有关报道也日渐增多。近三年来,笔者在五台山区从事前震旦纪变质沉积铁矿研究,曾按不同地层、不同岩石类型采集了一批样品,进行稀土元素含量测试。本文就是对其结果的初步研究。主要目的试图探索五台山区变质岩系不同构造层、不同岩石类型中稀土元素丰度及分配型式的变化,以便为本区变质地层的划分、变质岩的原岩恢复提供某些信息。

DISTRIBUTIONAL CHARACTERISTICS OF THE RARE EARTH ELEMENTS IN METAMORPHIC ROCKS FROM WUTAI MOUNTAIN REGION, SHANXI

According to the recent studies the formerly defined Wutai Group is subdivided into two parts: the lower part is named as Shizui Group and the upper part as Wutai Group. The authors of this paper try to demonstrate the distributional characteristics of REE in meta-morphic rocks from Shizui Group and Wutai Group.The differences of the distributional characteristics of REE between Shizui Group and Wutai Group are as follows.The total abundance of REE in Shizui Group is 66.1-416.4 ppm, LREE/HREE = 2.4-18.1. While in Wutai Group the total abundance of REE is 57.9-189.9 ppm, LREE/HREE= 1.8-6.3. But the average content of HREE of both is similar. So that the difference of total abundance is attributed to the enrichment of the light rare earth elements.The total REE contents in the individual specimen of chlorite-schists in Wutai Group are from 57.9 ppm to 108.0 ppm, and resemblance to those of the tholeiite and greenstone from the Mid-Atlantic Ridge and Hawaii.The chondrite-normalized REE distributional pattern displays a curve dipping towards HREE at steeper angle in Shizui Group, but the curve of Wutai Group rock is relatively gentle. The chondrites-normalized REE pattern of Wutai Group shows a negative anomaly at Ce and a positive anomaly at Eu. But the pattern of Shizui Group does not show any anomaly of Eu and the negative anomaly of Ce is not so obvious. The pattern of chlorite-schists from Wutai Group is similar to some tholeiites.The differences of REE distribution between the Shizui Group and Wutai Group suggest that both group possibly belong to a result of different geological history implying that there is an unconformity, e.i. the unconformity of Taihuai.