雷州半岛玄武岩母质土壤剖面稀土元素分布及其与常量元素、粒度的关系

RARE EARTH ELEMENTS DISTRIBUTION AND ITS CORRELATION WITH MACRO ELEMENTS AND PARTICLE-SIZE OF BASALT-DERIVED SOILS IN LEIZHOU PENINSULA

对雷州半岛玄武岩母质土壤剖面稀土元素地球化学特征进行了研究,结果表明:土壤剖面中稀土元素的分布既受母岩的控制,又叠加了风化成壤作用的影响,∑REE和δEu对母岩有明显的继承性,风化成壤作用则导致REE在剖面上部富集以及土壤中Ce的显著正异常,并造成轻、重稀土之间发生一定的分馏(以轻稀土富集为主要特征),但轻稀土或重稀土内部未出现明显的分异;∑REE与Fe2O3含量呈极显著负相关,可能与风化成土过程中铁氧化物结晶程度提高,富含REE的无定形铁含量降低有关;∑REE与P2O5、MnO则呈极显著正相关,应当是由于剖面中含有较多的赋存REE的磷酸盐矿物和锰氧化物矿物所致;∑REE与黏粒组分(尤其是<1μm的组分)呈极显著正相关,表明风化成壤过程中黏土矿物含量增加所导致的对REE的吸附效应是造成该区REE富集的重要原因,其中黏粒对轻稀土元素的吸附更为明显。

Geochemical characteristics of rare earth elements （REEs） in basalt-derived soil profiles in Leizhou Peninsula were studied. Results show that REE distribution in the soil profiles is not only controlled by their parent basahs, but also affected by weathering and soil forming processes. ∑REE and δEu demonstrate clear inheritance of basahs, while the weathering and soil forming processes result in REEs enrichment in the upper horizons of the profiles and obvious Ce positive anomaly and slight fractionation between light rate earth elements （LREEs） and heary rare earth elements （HREEs）, but no remarkable fractionation is observed in LREEs or in HREEs during the soil forming process. ∑REE shows an extremely significant negative correlation with Fe203 content, which may be attributed to enhanced Fe-oxides crystallization and decrease in content of REE-rich amorphous iron, while an extremely significant positive one with the contents of P2O5 and MnO, which should be caused by the existence of REEs-containing phosphate and Mn-oxides miner- als, and with the content of clay （especially the fraction 〈 1 μm） as well, demonstrating that the adsorption of REEs by clay minerals that are increasing during the weathering and soil forming processes is an important factor for the enrichment of REEs. Furthermore, the adsorption of LREEs by clay minerals is more obvious.