Experimental constraints on Fe isotope fractionation during magnetite and Fe carbonate formation coupled to dissimilatory hydrous ferric oxide reduction

Johnson, Clark M.; Roden, Eric E.; Welch, Susan A.; Beard, Brian L.

doi:10.1016/j.gca.2004.06.043

Cited by 218 publications

(202 citation statements)

References 92 publications

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“…Very similar values have been reported for the Kuruman BIF in the Transvaal Basin, South Africa , and the Biwabik BIF (Frost et al, 2007) which have been interpreted as resulting from a coupled diagenetic formation process of siderite and magnetite due to DIR. Experimental work by Johnson et al (2005) has revealed an equilibrium fractionation factor ∆ siderite-magnetite of -1.3‰ for DIR, whereas Johnson et al (2008) prefer a fractionation factor of -1.8‰ (see Table 5). An ankeritic component would increase the fractionation factor (Polyakov and Mineev, 2000;Johnson et al, 2005, see Table 5).…”

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Steinhoefel

Horn

Blanckenburg

2009

Geochimica et Cosmochimica Acta

136

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We have detected micrometer-scale differences in Fe and Si stable isotope ratios between coexisting minerals and between layers of banded iron formation (BIF) using an UV femtosecond laser ablation system connected to a MC-ICP-MS. In the magnetite-carbonate-chert BIF from the Archean Old Wanderer Formation in the Shurugwi Greenstone Belt (Zimbabwe), magnetite shows neither intra-nor inter-layer trends giving overall uniform  56 Fe values of ~0.9‰, but exhibits intra-crystal zonation. Bulk iron carbonates are also relatively uniform at near-zero values, however their individual  56 Fe value is highly composition-dependent: both siderite and ankerite and mixtures between both are present, and  56 Fe end member values are 0.4‰ for siderite and -0.7‰ for ankerite. The data suggest either an early diagenetic origin of magnetite and iron carbonates by the reaction of organic matter with ferric oxyhydroxides catalysed by Fe(III)-reducing bacteria; or more likely an abiotic reaction of organic carbon and Fe(III) during low-grade metamorphism. Si isotope composition of the Old Wanderer BIF also shows significant variations with  30 Si values that range between -1.0 and -2.6‰ for bulk layers. These isotope compositions suggest rapid precipitation of the silicate phases from hydrothermal-rich waters. Interestingly, Fe and Si isotope compositions of bulk layers are covariant and are interpreted as largely primary signatures. Moreover, the changes of Fe and Si isotope signatures between bulk layers directly reflect the upwelling dynamics of hydrothermal-rich water which govern the rates of Fe and Si precipitation and therefore also the development of layering. During periods of low hydrothermal activity, precipitation of only small amounts of ferric oxyhydroxide was followed by complete reduction with organic carbon during diagenesis resulting in carbonate-chert layers. During periods of intensive hydrothermal activity, precipitation rates of ferric oxyhydroxide were high, and subsequent diagenesis triggered only partial reduction, forming magnetite-carbonate-chert layers. We are confident that our micro-analytical technique is able to detect both the solute flux history into the sedimentary BIF precursor, and the BIF's diagenetic history from the comparison between coexisting minerals and their predicted fractionation factors.

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Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Steinhoefel

Horn

Blanckenburg

2009

Geochimica et Cosmochimica Acta

136

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“…Previous spectroscopic studies indicate that co-precipitation of Fe(III) and Si from a mixed solution tends to form an intimately bonded Fe(III)-Si phase, rather than separate Fe(III) and Si phases (Doelsch et al, 2000(Doelsch et al, , 2001(Doelsch et al, , 2003. Identifying the specific primary Fe(III) precipitate in IFs is important, because when exposed to dissolved Fe(II), Fe(III)-Si gels are resistant to phase transformations that may occur in dissolved Fe(II)-ferrihydrite experiments (e.g., Johnson et al, 2005), and uptake of Fe(II) into the solid is inhibited under abiological conditions (Fig. 7).…”

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confidence: 99%

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

Konhauser

Planavsky

Hardisty

et al. 2017

Earth-Science Reviews

382

257

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“…It can be inferred from these diverse signatures that iron isotopes will bring new constraints on DFe sources to the ocean. In addition, several processes involved in the iron cycling within the water column (e.g., biological uptake, remineralization, scavenging, adsorption, desorption, dissolution, precipitation, organic complexation, and redox processes) may fractionate iron isotopes (14,(18)(19)(20)(21)(22). Hence, such isotopic fractionations may also bring additional constraints on the iron cycle within the water column.…”

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confidence: 99%

Iron isotopes reveal distinct dissolved iron sources and pathways in the intermediate versus deep Southern Ocean

Abadie

Lacan

Radic

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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As an essential micronutrient, iron plays a key role in oceanic biogeochemistry. It is therefore linked to the global carbon cycle and climate. Here, we report a dissolved iron (DFe) isotope section in the South Atlantic and Southern Ocean. Throughout the section, a striking DFe isotope minimum (light iron) is observed at intermediate depths (200–1,300 m), contrasting with heavier isotopic composition in deep waters. This unambiguously demonstrates distinct DFe sources and processes dominating the iron cycle in the intermediate and deep layers, a feature impossible to see with only iron concentration data largely used thus far in chemical oceanography. At intermediate depths, the data suggest that the dominant DFe sources are linked to organic matter remineralization, either in the water column or at continental margins. In deeper layers, however, abiotic non-reductive release of Fe (desorption, dissolution) from particulate iron—notably lithogenic—likely dominates. These results go against the common but oversimplified view that remineralization of organic matter is the major pathway releasing DFe throughout the water column in the open ocean. They suggest that the oceanic iron cycle, and therefore oceanic primary production and climate, could be more sensitive than previously thought to continental erosion (providing lithogenic particles to the ocean), particle transport within the ocean, dissolved/particle interactions, and deep water upwelling. These processes could also impact the cycles of other elements, including nutrients.

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Experimental constraints on Fe isotope fractionation during magnetite and Fe carbonate formation coupled to dissimilatory hydrous ferric oxide reduction

Cited by 218 publications

References 92 publications

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

Iron isotopes reveal distinct dissolved iron sources and pathways in the intermediate versus deep Southern Ocean

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