globalchange  > 气候变化与战略
DOI: 10.1016/j.epsl.2020.116083
论文题名:
Molybdenum isotope fractionation in glacial diamictites tracks the onset of oxidative weathering of the continental crust
作者: Greaney A.T.; Rudnick R.L.; Romaniello S.J.; Johnson A.C.; Gaschnig R.M.; Anbar A.D.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 534
语种: 英语
中文关键词: continental crust ; great oxidation event ; isotope fractionation ; molybdenum ; weathering
英文关键词: Binary alloys ; Glacial geology ; Groundwater ; Igneous rocks ; Iron alloys ; Iron oxides ; Isotopes ; Manganese alloys ; Molybdenum ; Oxidation ; Atmospheric oxygen ; Continental crusts ; Great Oxidation Event ; Isotope fractionation ; Molybdenum isotopes ; Oxidative conditions ; Oxidative weathering ; Upper continental crust ; Weathering ; Archean ; continental crust ; diamictite ; glacial deposit ; isotopic fractionation ; molybdenum ; oxidation ; sediment chemistry ; weathering
英文摘要: Molybdenum isotopes in twenty-four composites of glacial diamictites spanning depositional ages of 2900 to 300 Ma show a systematic shift to lighter compositions and a decrease in Mo concentration over time. The diamictites fall into three age groups relative to the Great Oxidation Event (GOE): pre-GOE (2.43 – 2.90 Ga), syn-GOE (2.20 – 2.39 Ga), and post-GOE (0.33 – 0.75 Ga). Pre-GOE composites have an average δ98MoNIST3134 of +0.03‰ (± 0.18‰), syn-GOE composites average −0.29‰ (± 0.60‰), and post-GOE composites average −0.45‰ (± 0.51‰). These groups are statistically different at p=0.05. We use the pre-GOE data to estimate the average Archean upper continental crust (UCC) δ98Mo signature as +0.03 ± 0.18‰ (2σ), which falls within the range of previous estimates of modern igneous rocks. As the diamictites represent a mixture of igneous and weathered crust, the shift to lighter Mo values over time likely reflects Mo isotope fractionation during oxidative weathering and increased retention of light Mo isotopes in weathered regolith and soils. We hypothesize that this fractionation is due to the mobilization of oxidized Mo following the GOE, and subsequent adsorption of light Mo onto Fe-Mn oxides and/or organic matter in weathered regolith. We conclude that Mo isotopes in continental weathering products record the rise of atmospheric oxygen and onset of oxidative weathering. As the regolith formed under oxidative conditions is isotopically lighter than average continental igneous rocks, mass balance dictates that Mo isotope fractionation during oxidative weathering should result in isotopically heavy groundwater and river water, which is observed in modern systems. © 2020 Elsevier B.V.
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资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/164995
Appears in Collections:气候变化与战略

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作者单位: Department of Earth Science and Earth Research Institute, University of California - Santa Barbara, Santa Barbara, CA 93106, United States; Department of Geology, University of Maryland - College Park, College Park, MD 20742, United States; School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, United States; Department of Earth and Planetary Sciences, University of Tennessee - Knoxville, Knoxville, TN 37996, United States; Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts - Lowell, Lowell, MA 01854, United States; School of Molecular Sciences, Arizona State University, Tempe, AZ 85281, United States

Recommended Citation:
Greaney A.T.,Rudnick R.L.,Romaniello S.J.,et al. Molybdenum isotope fractionation in glacial diamictites tracks the onset of oxidative weathering of the continental crust[J]. Earth and Planetary Science Letters,2020-01-01,534
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