花岗闪长岩和玄武岩风化过程中的稀土元素分异  

Fractionation of rare earth elements in the weathering processes of granodiorite and basalt

作　　者：陈庆华 苏妮[1] 杨承帆 杨守业[1] CHEN Qing-hua;SU Ni;YANG Cheng-fan;YANG Shou-ye(State Key Laboratory of Marine Geology,Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学海洋地质国家重点实验室,上海200092

出　　处：《矿物岩石地球化学通报》2024年第4期829-842,共14页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：国家自然科学基金资助项目(42173008);上海市自然科学基金资助项目(23ZR1466900)。

摘　　要：稀土元素(REE)在表生风化过程中表现出独特的分布规律与分异特征,对于示踪化学风化和成土过程意义重大。本研究对湖南攸县玄武岩风化剖面样品进行了酸淋滤处理(1 mol/L HCl淋滤),并分别测试了残渣态、酸溶态组分的元素地球化学组成。结合前人在福建仙游花岗闪长岩剖面的矿物学及元素地球化学数据,对比研究了花岗闪长岩和玄武岩风化过程中的稀土元素分异行为。结果表明,仙游剖面与攸县剖面全岩样轻、重稀土分异特征受原生矿物(如富稀土难溶副矿物、斜长石)影响明显,多代表成土母质信息;两剖面的酸溶态组分轻、重稀土分异特征与次生黏土矿物组成相关(高岭石影响明显,蒙脱石无影响),多反映环境信息;pH值变化以促进磷酸盐矿物溶解的方式深刻影响着中稀土元素行为,因此酸溶态组分的中稀土元素组成信息不具地质意义。研究揭示,通过对风化剖面酸溶态组分稀土含量参数(ΣREE)及轻、重稀土分异程度参数(La/Yb)P的联用,可有效消除岩性(成土母质)因素的影响,精确示踪风化成土过程的不同阶段,从而可以作为剖面风化程度的替代性指标。Rare earth elements(REE)have unique distribution regularities and fractionation characteristics in the epigenetic weathering process,and are of great significance for tracing chemical weathering and pedogenesis processes.In this study,the acid leaching treatment(leached by 1 mol/L HCl)has been applied to treat samples from a basalt weathering profile in Youxian County,Hunan Province,and elemental geochemical compositions of the residual and acid-soluble fractions of treated samples have been analyzed.Combining with the mineralogical and geochemical data of samples from a granodiorite weathering profile in Xianyou County,Fujian Province,we have carried out a comparitive study on the REE fractionation behaviors in the weathering processes of granodiorite and basalt.The results show that the fractionation characteristics of light and heavy REE in all weathered rock samples from the Xianyou and Youxian profiles are obviously influenced by their primary minerals(such as REE-enriched insoluble accessory minerals and plagioclase),which mostly represent the parent material information of weathering profile samples.The light and heavy REE fractionation characteristics of acid-soluble fractions of samples from the two profiles are related to the compositions of secondary clay minerals(with obvious influence by kaolinite,but no effect by montmorillonite),which mostly reflect the environmental information of weathering profile.The change of pH values greatly affects the fractionation behavior of middle REE by promoting the dissolution of phosphate minerals,so the compositional information of middle REE in the acid-soluble fractions of samples is not of geological significance.This study reveals that the combination of the REE content index(ΣREE)and REE fractionation index(La/Yb)P of acid-soluble fractions of samples can be applied to effectively eliminate the influence of lithological(parent material)factors,to precisely trace different stages of weathering and pedogenesis processes,and to be used as an alternative index fo

关 键 词：风化剖面 风化阶段 稀土元素分异 酸溶态组分 

分 类 号：P595[天文地球—地球化学] P512.1[天文地球—地质学]