摘要
网纹红土是南方红土中最具标志性的地层之一。本文以中亚热带地区典型网纹红土样品为研究对象,针对网纹红土原样及其分离出的红基质和白网纹3类样品的全样、<2μm、2~4μm、4~10μm、10~32μm、32~63μm和>63μm等不同粒级组分样品的稀土元素(REE)进行分析,研究中国南方网纹红土中红基质、白网纹和分粒级组分的REE分馏特征。结果显示:①白网纹的ΣREE和各稀土元素含量均明显高于红基质,主要原因是白网纹中含有较多的锆石及高岭石等黏土矿物,也可能是稀土元素在两者之间的迁移导致了相对含量的变化。红基质Ce异常均大于白网纹的现象,指示了网纹的形成可能与氧化还原环境的差异有关;②网纹红土中REE含量存在明显的粒级效应,>2μm的粒级组分中,REE含量随着粒级增大而降低。网纹红土中<2μm组分的REE总量较低,可能与该粒级副矿物类型有关,相对酸性的环境对其影响有限;③不同样品间球粒陨石标准化稀土元素配分模式基本一致。在<32μm组分中,红基质和白网纹的LREE/HREE、Eu/Eu*等特征参数均十分接近,并与全样一致,而在>32μm组分中存在明显差异。>32μm组分中红基质和白网纹La/Nd、Eu/Sm等稳定元素比值十分接近,表明红基质和白网纹物源相同;④网纹红土各粒级组分地球化学特征更接近长江漫滩沉积物,揭示网纹红土的潜在物源主要为长江漫滩沉积。
Vermicular red earth is the most symbolic strata in the cumulic red earth in southern China.This study focused on seven typical vermicular red earth samples collected from different sections in subtropical China and all samples were classified in three groups,namely,original vermicular red earth,red matrix,and white mottles samples.Each group,including bulk samples,was then separated into seven subsamples based on its particle size as<2,2−4,4−10,10−32,32−63,and>63μm.The rare earth elements(REE)of these 147 subsamples were investigated to analyze the difference between red matrix and white mottles,and their variations along with particle size changes.Our preliminary findings showed that:(1)The concentrations of REE of white mottles were obviously higher than that of red matrix,which was ascribed to the concentrations of clay minerals,zircon enrichment,and element migrations;(2)The REE concentrations in vermicular red earth with>2μm showed an obvious decreasing trend with increase in the particle size.The lower REE in<2μm component of vermicular red earth may be attributed to the presence of accessory minerals,and relatively acidic environment has limited impact on it;(3)Highly similar chondrite-normalized REE patterns were observed among different vermicular red earth samples.LREE/HREE and Eu anomalies among red matrix,reticulated mottles,and the original vermicular red earth were similar in the finer sediment(<32μm)but clearly distinct in the coarser sediments(>32μm).The high similarity of stable REE ratios(La/Nd,Eu/Sm)between red matrix and white mottles indicated that they have similar provenance;(4)We analyzed the ratio of immobile elements between vermicular red earth and potential source area,suggesting that sediments of the Yangtze River are provenance of vermicular red earth.
作者
张忠萍
朱丽东
马桢桢
黄颖
于红梅
李凤全
张杭佳
王天阳
叶玮
ZHANG Zhongping;ZHU Lidong*;MA Zhenzhen;HUANG Ying;YU Hongmei;LI Fengquan;ZHANG Hangjia;WANG Tianyang;YE Wei(College of Geography and Environmental Sciences,Zhejiang Normal University,Jinhua 321004,Zhejiang,China)
出处
《地球化学》
CAS
CSCD
北大核心
2023年第5期582-594,共13页
Geochimica
基金
浙江师范大学流域地表过程与生态安全重点实验室开放基金课题(KF-2022-04)
国家自然科学基金项目(41572345、41971111)联合资助。
关键词
网纹红土
稀土元素
分粒级
红基质
白网纹
vermicular red earth
rare earth elements
particle size fraction
red matrix
white mottles
