Fractionation of rare earth elements in the weathering processes of granodiorite and basalt
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 for judging the weathering intensity of the relevant weathering profile.
weathering profileweathering stagerare earth elements fractionationacid-soluble fraction
万方数据
维普
