贵州碳酸盐岩风化壳主元素、微量元素及稀土元素的地球化学特征

摘要

Guizhou Plateau is located in the east of Yunnan-Guizhou Plateau, where variable karst landscapes are widely distributed. The major, trace and rare earth elements of a typicalin-situ weathering profile of carbonate rock on karst terrain of Guizhou Plateau have been researched to provide evidence of elements’ geochemical behaviours in the weathering crust. The results indicate thatthesamples are characterized by enrichment in Pb and Co and depletion in Sr, Na, Ba, K, Rb and Cr in the profile according toupper continental crust (UCC)normalized spiderdiagram of samples. The total amount of REEsranges between167.4~1814.2μg/g. REEsdecrease gradually fromlowerto upper regolith of the profile and LREEs show more leaching than HREEs in the middle and upper part of the profile. The element Ce has been separated from the other REEs, chondrite-normalized REEs distribution patterns show significant Ce-anomalies and slight negative Eu-anonalies. Ce shows negative anomalies in the lower partof theregolithin weathering front,but positive anomaliesin the upper part. In addition, the concentration of elements in rock-soil interface grows by an average of 21 timesmorethan that in the rock powder, whichshows a clear mutation of alkaline barrier near the rock-soil interface. Our research shows that the variations of major and trace elements are well correlated in the weathering profile, indicatingthatthey have the same geochemical behaviors during the weathering process.Ferruginous nodular horizon contains the lowest REEs,which issimilarin the case of upper continental crust (UCC),and we believe that this can be referred toin researching the relation between UCC and ferruginous nodular horizon of carbonate rocks.%选取贵州高原喀斯特地区的典型碳酸盐岩原生风化剖面为研究对象,研究主元素、微量元素及稀土元素在风化壳的迁移转化及其分布规律特征,为解释碳酸盐岩风化壳元素的地球化学变化提供依据。结果显示,从上陆壳标准化蛛网图可知, Pb、Co在剖面富集,而Na、K、Cr、Rb、Sr和Ba则亏损。风化壳∑REE的变化范围为167.4~1814.2μg/g,稀土元素从剖面下部往上逐渐减少,剖面中上部LREE比HREE淋滤程度大。稀土元素球粒陨石标准化后Ce正负异常, Eu轻微负异常。以风化前缘为分界,在风化前缘以下的土层, Ce负异常,风化前缘以上的土层, Ce正异常。此外,在风化壳岩土界面附近存在一个明显且突变的碱性障,岩土界面土样的元素含量较岩粉平均增加了21倍。我们的研究显示,风化剖面主元素和微量元素的变化波动特征较为一致,说明主元素和微量元素在风化过程中的地球化学行为较为一致。铁壳层中稀土元素的含量最低,与上陆壳稀土元素十分相近,为研究上陆壳与碳酸盐岩铁壳层之间的相互联系起到了一定的借鉴作用。