Effects of changing solution chemistry on Fe3+/Fe2+ isotope fractionation in aqueous Fe–Cl solutions

Iron isotope fractionation in subduction-related high-pressure metabasites (Ile de Groix, France)

“…Recent studies have shown that variations in the nature and mode of metasomatic processes result in variable effects on Fe isotope composition of mantle rocks (Weyer and Ionov 2007;Poitrasson et al 2013). Fe solubility, transport and isotope fractionation in subduction zone fluids strongly depends on its oxidation state and relative abundance, as well as on the fluid composition (Polyakov and Mineev 2000;Manning 2004;Hill et al 2010;Debret et al 2014Debret et al , 2016. Our results confirm that the subducted oceanic crust may be a source for mantle iron isotope heterogeneities at different depth levels:…”

“…in the ligand composition (chloride, sulfide), as well as in the speciation, relative abundances, coordination number of Fe 2+ and Fe 3+ , and in the ionic strength of the solution (Hill et al 2010). Changes in the chemistry of Fe-bearing solutions have major implications on the isotopic composition of Fe-precipitates: Fe redox isotope fractionation between Fe 2+ -and Fe 3+ -bearing species decreases with decreasing chlorinity, while it is more sensitive to changes in ferric speciation than in ferrous speciation (Hill et al 2010).…”

Fe isotope fractionation during phase separation in the NaCl–H2O system: An experimental study with implications for seafloor hydrothermal vents

“…Fe solubility and the relative distribution of aqueous Febearing species are undoubtedly sensitive to these compositional changes (Bischoff and Rosenbauer, 1987;Ding and Seyfried, 1992;Testemale et al, 2009). Although it is well known that Fe isotope fractionation is significantly affected by redox (Fe 2+ -Fe 3+ exchange in a hydrated aqueous species, Hill et al, 2010), this is unlikely at any stage in the present experiment, owing to the highly reducing conditions imposed by the presence of H 2 (aq) from decomposition of formic acid. In effect, redox was buffered throughout the experiment, such that valence change of iron to the ferric species was not possible.…”

“…Theoretical calculations (Hill and Schauble, 2008;Hill et al, 2009Hill et al, , 2010Schauble et al, 2001) have confirmed that differences in coordination chemistry between Fe chloro-and aquocomplexes can result in Fe isotope fractionation comparable in magnitude to reduction-oxidation processes, where the predicted fractionation between two Fe-bearing phases/species is described by the difference in reduced partition function ratios, β (i.e. isotope affinity), 10 3 ln α a/b = 10 3 (ln β a − ln β b ).…”

Isotope Fractionation Processes of Selected Elements

“…Changes in bond partners and/or coordination number also have an effect on isotope fractionation (Hill et al 2009(Hill et al , 2010, implying that Fe isotope compositions reflect both the redox state and the solution chemistry.…”