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Absolute accumulation and isotope fractionation of Si and Fe during dolomite weathering and terra rossa formation
Feng, JL (Feng, Jin-Liang)1; Pei, LL (Pei, Le-Le)1,2; Zhu, XK (Zhu, Xiangkun)3; Ju, JT (Ju, Jian-Ting)1; Gao, SP (Gao, Shao-Peng)1
Source PublicationCHEMICAL GEOLOGY
2018-09-30
Volume496Issue:0Pages:43-56
DOI10.1016/j.chemgeo.2018.08.018
Abstract

The behavior of silicon (Si) and iron (Fe) and their isotope fractionation during carbonate weathering and terra rossa formation are unclear. Here, we focus on a 4.05-m-thick terra rossa profile developed on dolomite in the Yunnan-Guizhou Plateau, China. We measured the mineral and geochemical composition, magnetic susceptibility and Si and Fe isotopic composition of the terra rossa, ferromanganese concretions (FMCS), and the dolomite and its insoluble residues. The results indicate that there is absolute accumulation of Si and Fe during dolomite weathering and terra rossa formation, due to the extraneous input of dissolved Si and Fe. This means that the insoluble residues of dolomite are not the only source for terra rossa formation. In addition, we suggest that the high frequency-dependent magnetic susceptibility (chi(fd), %) and rubification of the terra rossa are the result of the oxidation of extraneous dissolved Fe and the neoformation of finely dispersed Fe oxides. Overall, the terra rossa is characterized by the enrichment of light Si and Fe isotopes, compared with insoluble dolomite residues and bulk dolomite. The extraneous input of dissolved Fe is characterized by a light isotopic signature, whereas the Si isotopic signature of the extraneous source is unclear due to modification by late desilicification. Si isotope fractionation in the terra rossa is mainly controlled by chemical weathering and associated mobilization and redistribution of Si. The delta Si-30 values of terra rossa decrease with increasing weathering intensity, while the re-precipitation of mobilized Si leads to the significant enrichment of isotopically heavy Si in the basal terra rossa. The delta Si-30 values of terra rossa are not significantly affected by the adsorption of the Fe and Al (oxyhydr)oxides. By contrast, the major process that fractionates Fe isotopes in the dolomite-terra rossa weathering system is unclear. In the terra rossa profile, the delta Fe-56 values of the FMCS are significantly lower than those of the surrounding terra rossa matrix. These low delta Fe-56 signatures of the FMCS reflect the preferential translocation of the light Fe isotope, while the FMCS may be able to record the low-delta Fe-56 characteristics of pore water.

Subject Area地理学
WOS IDWOS:000444923600005
Language英语
Indexed BySCIE
KeywordYunnan-guizhou Plateau Iron-oxide Mineralogy Rare-earth-elements Silicon Isotopes Soil Chronosequence Geochemical Cycle Dissolved Silicon Genesis Basalt China
WOS Research AreaGeochemistry & Geophysics
WOS SubjectGeochemistry & Geophysics
Cooperation Status国内
ISSN0009-2541
Department环境变化与地表过程重点实验室
PublisherELSEVIER SCIENCE BV
Citation statistics
Cited Times:1[WOS]   [WOS Record]     [Related Records in WOS]
Document Type期刊论文
Identifierhttp://ir.itpcas.ac.cn/handle/131C11/8541
Collection图书馆
Corresponding AuthorFeng, JL (Feng, Jin-Liang)
Affiliation1.Chinese Acad Sci, Inst Tibetan Plateau Res, Key Lab Tibetan Environm Changes & Land Surface P, Beijing 100101, Peoples R China;
2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China;
3.Chinese Acad Geol Sci, Inst Geol, MNR Key Lab Isotope Geol, Beijing 100037, Peoples R China.
Recommended Citation
GB/T 7714
Feng, JL ,Pei, LL ,Zhu, XK ,et al. Absolute accumulation and isotope fractionation of Si and Fe during dolomite weathering and terra rossa formation[J]. CHEMICAL GEOLOGY,2018,496(0):43-56.
APA Feng, JL ,Pei, LL ,Zhu, XK ,Ju, JT ,&Gao, SP .(2018).Absolute accumulation and isotope fractionation of Si and Fe during dolomite weathering and terra rossa formation.CHEMICAL GEOLOGY,496(0),43-56.
MLA Feng, JL ,et al."Absolute accumulation and isotope fractionation of Si and Fe during dolomite weathering and terra rossa formation".CHEMICAL GEOLOGY 496.0(2018):43-56.
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