摘要
为了解风化壳中离子交换相稀土元素的特征,对广西某地花岗岩风化壳剖面样品进行了X射线衍射及主量、稀土元素地球化学特征的研究.剖面自上而下可划分为腐殖土层(A1)、亚粘土层(A2)、网纹状风化层(B1)和全风化层(B2);自A1至B2,粘土矿物的含量和化学风化蚀变指数快速降低;与母岩相比A1、A2、B1中全相Ce、Nd和HREE相对富集,B2中全相稀土与母岩特征相似,所有样品的离子交换相HREE亏损,Y相对富集;离子交换相轻、重稀土一起富集在B2中.据此推测,花岗岩中褐帘石、榍石等易风化的稀土矿物为离子交换相稀土提供了主要的物源,锆石、磷钇矿等难风化的稀土矿物的残留及表生稀土矿物的形成使全相HREE相对富集;离子交换相轻、重稀土元素的分馏程度随风化程度的增加而变化.
X-ray diffraction（XRD）,major and rare earth elements（REEs）geochemical characteristics of samples in a weathering profile from Guangxi were studied in order to reveal the geochemical behaviors of REEs during weathering.The profile can be divided into four layers from surface downwards：the humic layer（A1）,the sub-clay layer（A2）,the net-veined weathered layer（B1）,and the completely weathered layer（B2）.Clay minerals and chemical indexes of alteration（CIA）rapidly decrease from top to bottom.Samples from A1,A2 and B1 are enriched in Ce,Nd and heavy REE relative to their parent rocks.All samples are depleted in ion-exchangeable heavy REE and are relatively enriched in Y.Ion-exchangeable light and heavy REEs are enriched in the completely weathered layer.The ion-exchangeable REEs in the weathered granite are sourced mainly from labile REE-bearing minerals,such as allanite and titanate.The enrichment of heavy REE in samples from A1,A2 and B1 may have been caused by the residual zircon and xenotime,or the formation of supergene mineral,such as churchite-Y.The degree of weathering of granite leads to the change of the fractional degree of ion-exchangeable light and heavy REE.
作者
赵芝
王登红
潘华
屈文俊
Zhao Zhi Wang Denghong Pan Hua Qu Wenjun(Key Laboratory of Metallogeny and Mineral Resource Assessment of Ministry of Land and Resources （MLR）, Institute of Mineral Resources Chinese Academy of Geological Sciences, Beijing 100037, China Guangxi Geological Survey, Nanning 530023, China National Research Center for Geoanalysis, Beijing 100037,China)
出处
《地球科学（中国地质大学学报）》
EI
CSCD
北大核心
2017年第10期1697-1706,共10页
Earth Science-Journal of China University of Geosciences
基金
中央级公益性科研院所基本科研业务费专项资金(No.K1506)
中国地质调查局地质大调查项目(No.DD20160056)
关键词
风化壳剖面
稀土元素
离子交换相稀土
风化程度
花岗岩
地球化学
weathering profile
rare earth element
ion-exchangeable REE
weathering degree
granite
geochemistry.
