老挝南部Antoun地区花岗闪长岩风化壳中常量和稀土元素分布  

DISTRIBUTION OF MAJOR ELEMENTS AND REE IN WEATHERING CRUST OF GRANODIORITE IN ATTAPEU PROVINCE,PDR OF LAO

作　　者：杨社锋[1,2,3] 方维萱[1,2] 胡瑞忠[1] 王思德[2] 魏宁[2] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室,贵阳550002 [2]有色金属矿产地质调查中心,北京100012 [3]中国科学院研究生院,北京100049

出　　处：《土壤学报》2009年第2期201-209,共9页Acta Pedologica Sinica

基　　金：中国科学院地球化学研究所矿床地球化学国家重点实验室开放基金(200303);财政部中央财政补助项目“老挝中南部铜多金属矿产前期概查与选区”(财建2004[227]号)资助

摘　　要：应用岩石薄片鉴定、X射线粉晶衍射、X射线荧光光谱和ICP-MS等分析方法,研究了热带季风型气候条件下老挝Attapeu省Antoun地区二叠纪花岗闪长岩上发育的砖红土型风化壳矿物组成、常量元素和稀土元素地球化学特征。结果表明,风化产物呈酸性,风化壳表土上形成薄层硅质壳层,表土中石英含量最高、铁氧化物含量低和高岭石含量低,符合典型的灰化土特征。随着风化作用加强,Fe2O3、TiO2和Al2O3出现富集,K2O、Na2O、CaO和MgO出现淋失。石英出现富集原因可能是雨季降水冲刷和酸性水淋溶掉高岭石等黏土矿物,而旱季SiO2含量上升至地表富集形成硅质薄壳缘故。剖面稀土元素分布型式为轻稀土富集型,∑REE在风化壳中部达到最高值318 mg kg-1,剖面上Ce和Eu均呈正异常-负异常-正异常变化趋势,∑REE最高值出现在Ce和Eu负异常和(Fe2+/Fe3+)较高层位,∑REE与Fe2O3显著正相关。REE富集与铁铝氧化物和黏土矿物吸附有关,也与相对还原的酸性环境有关。The composition and distribution of mineral, major elements and rare earth elements （REE） in the granodiorite weathering crust in Antoun area in Attapeu Province of PDR of Lao was determined by means of rock thin section, XRD, XRF and ICP-MS etc. Results show all the samples, except for granodiorite, are acid. There is a thin siliceous crust on the top soil of the weathering profile. Quartz content reaches the highest in top soil where kaolinite and iron oxide contents are lower than layer under it. These are some typical characteristics of Spodosols. With intensifying weathering reaction, Fe2O3, TiO2 and Al2O3 are enriched, and Na2O, CaO and MgO, K2O are leached in weathering material. It is assumed that some clay minerals in the top soil are washed away by rainfall and leached by acid solution in wet season, and that SiO2 moves up to the top soil from the lower layers in dry season. The Chondrite normalized REE pattern shows typical enrichment of LREE, with ∑ REE peaking up to 318 mg kg^-1 in central layer of the profile. Both Ce and Eu have a similar trend of variation in the profile, i.e. positive anomaly-negative anomaly-positive anomaly from bottom to top. The highest ∑ REE value occurs where negative Ce and Eu anomaly and relatively higher Fe^2＋/Fe^3＋ values also occur. Furthermore, there is a relatively significant correlation between ∑ REE and Fe2O3 throughout the whole profile, reflecting that REE enrichment is related to adsorption of iron-aluminum oxides and relatively reductive-acid environment.

关 键 词：老挝 砖红土型风化壳 常量元素 稀土元素 

分 类 号：P611.2[天文地球—矿床学] O614.3[天文地球—地质学]