期刊
CHEMICAL GEOLOGY
卷 211, 期 3-4, 页码 343-362出版社
ELSEVIER
DOI: 10.1016/j.chemgeo.2004.07.002
关键词
iron-isotopes; isotope fractionation; siderite; green rust
Iron isotope fractionation between aqueous iron and siderite has been measured using abiotic synthesis experiments at similar to20 degreesC. Applying a Rayleigh distillation model to three experiments in which siderite (FeCO3) was continuously precipitated from solutions over the course of tens of hours, the derived fractionation factor is 10(3)Inalpha(Fe(II)-Siderite)=+0.48 +/- 0.22parts per thousand (2sigma). This experimentally determined fractionation factor is significantly smaller (by similar to1.5parts per thousand) than that calculated from vibrational frequencies and Mossbauer shifts [Geochim. Cosmochim. Acta 64 (2000) 849-865; Geochim. Cosmochim. Acta 65 (2001) 2487-2497], and lies on the high end of that inferred from natural mineral assemblages, where the Fe(II)(aq)-Siderite fractionation factor was inferred to lie between -1.7parts per thousand and +0.3parts per thousand [Contrib. Mineral. Petrol. 144 (2003) 523-547]. The measured Fe(II)(aq)-siderite fractionation from this study suggests that siderite from Archean and Proterozoic rocks, which have moderately negative delta(56)Fe values (-1.5parts per thousand to -0.5parts per thousand), may reflect precipitation from Fe(II)(aq) whose origin was hydrothermal. In contrast, natural siderites that have higher delta(56)Fe values apparently require non-hydrothermal sources of Fe and/or different pathways of formation, or may reflect the effects of cation substitution on the Fe(II)(aq)-carbonate fractionation factor. (C) 2004 Elsevier B.V. All rights reserved.
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