华南风化壳中稀土元素的分异作用及其影响因素

Fractionation of Rare earth Elements and its Effecting Factors in Weathering Crusts in South China

对华南风化壳剖面中稀土元素分布的研究结果，稀土元素的总量在各剖面的垂向上多呈抛物线型分布．轻稀土与重稀土之间、Ｃｅ和Ｅｕ与其它稀土元素之间在剖面中出现明显的分异作用．重稀土自上往下迁移的能力较强，在剖面的中下部相对富集．轻稀土在风化壳中比重稀土更加富集或更加贫化．Ｃｅ异常（δＣｅ）在垂向上的变化规律与稀土总量相反，在风化壳表层出现明显的正异常，而在全风化层中亏损．Ｅｕ异常（δＥｕ）在风化壳中自下而上有逐渐增大的趋势．影响风化壳中稀土元素的活动性和分异作用的因素有原岩的稀土分布及风化壳的矿物组合、Ｐｈ值、氧化还原条件、雨水和地下水以及有机质和微生物等．

The concentration of rare earth elements (REE) in some weathering profiles in South China shows that REE is distributed vertically in a parabolic form. The fractionation between LREE and HREE and that between Ce, Eu and other rare earth elements are obvious in the profiles. The HREE has a stronger ability to move downward and therefore is more enriched in the middle to lower parts of the profiles,whereas the LREE tends to be more enriched or depleted in the profiles. The distribution of Ce anomaly in the profiles is contrary to that of REE. The positive Ce anomaly is apparent in the surface layers of the profiles and Ce is depleted in the completely weathering layers. Eu anomaly tends to increase from the lower to the upper parts of the weathering profiles. The main effecting factors on the mobility and fractionation of REE include the distribution of REE in the original rocks, mineralogical assemblages of the weathering crusts, Ph value, oxidization reduction conditions, rain and underground water and organisms in the profiles.