秭归地区闪长岩岩体风化壳微量元素地球化学特征

通过对秭归地区闪长岩岩体风化壳中微量元素的分布规律研究，将该风化剖面中的微量元素划分为3类。第一类包括Sc、V、Cr、Co、Ni、Cu、Zn、Zr、Hf、Nb、Ta、U、Th、Mo、W，基本属于非活动性元素，在风化过程中得以有效保留，其中U、Cr、Cu等受氧化还原条件的影响，有时呈局部富集现象，规律性不明显。第二类以Ca、Rb、Cs、Sr、Ba、Pb、Ga、Gd、Tl为代表，随着风化作用的进行而逐步从风化壳中淋失，属活动性元素。第三类以稀土元素为代表，在风化壳内部发生局部的再分配，从剖面上层随风化溶液向下淋滤亏损，到剖面中下部沉淀富集，其中重稀土元素的淋失程度大于轻稀土元素。由于母岩中斜长石的风化淋滤，Eu在氧化环境下逐渐从正异常变为负异常。Ce在地表氧化条件下很容易生成四价氧化物（方铈石），并在表层明显富集，剖面介质中氧化还原条件的变化导致Ce的波动变化。

GEOCHEMICAL CHARACTERISTICS OF TRACE ELEMENTS IN THE DIORITE WEATHERED CRUST OF ZIGUI AREA

Based on studying the distribution of trace elements in the dioritic weathered crust of Zigui area,the authors have divided the trace elements into three types.The first type consists of inactive elements which include Sc,V,Cr,Co,Ni,Cu,Zn,Zr,Hf,Nb and Ta,U,Th,Mo,W.During the weathering process,they can be effectively preserved.Due to the influence of redox condition variation,U,Cr and Cu sometimes show local enrichment,without obvious regularity.The second type is composed of active elements such as Ca,Rb,Cs,Sr,Ba,Pb,Ga,Gd,and Tl,which are gradually leached from profiles along with the weathering.The third type is represented by REE,which are leached from the upper section downward,and enrichment is observed in the mid-lower section,with the leaching degree of HREE higher than that of LREE.Eu gradually changes from positive anomalies in parent rocks into negative anomalies on the surface due to the weathering leaching of plagioclase in parent rocks under the oxidation environment.Under the surface oxidation condition,Ce easily produces tetravalence oxides(cerianite) and shows obvious surface enrichment,and the variation of the redox conditions leads to the undulate variation of Ce.