XANES calibration for determining the oxidation state of iron in mantle garnet

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dc.contributor.authorBerry, AJen_AU
dc.contributor.authorYaxley, GMen_AU
dc.contributor.authorWoodland, ABen_AU
dc.contributor.authorForan, GJen_AU
dc.date.accessioned2010-11-28T23:28:16Zen_AU
dc.date.available2010-11-28T23:28:16Zen_AU
dc.date.issued2010-11-01en_AU
dc.date.statistics2010-11-01en_AU
dc.description.abstractIron K-edge X-ray absorption near edge structure (XANES) spectra were recorded for synthetic garnets of the almandine–skiagite (Fe3Al2Si3O12–Fe3Fe2Si3O12), andradite–skiagite (Ca3Fe2Si3O12–Fe3Fe2Si3O12), Fe–knorringite–skiagite (Fe3Cr2Si3O12–Fe3Fe2Si3O12), and andradite–grossular (Ca3Fe2Si3O12–Ca3Al2Si3O12) solid solutions. Fe3+/ΣFe varied systematically in these samples from 0 to 1. The variation in the energy and intensity of spectral features as a function of Fe3+/ΣFe was investigated to identify correlations that could be used to determine Fe3+/ΣFe of unknowns. The pre-edge energy, which is commonly used for quantification, was found to be relatively insensitive for garnet, particularly at low values of Fe3+/ΣFe. The best correlation was for the absorption edge energy, which may provide an accurate and precise method for determining Fe3+/ΣFe of garnets in metapelitic rocks. The resulting calibration curve, however, significantly and non-systematically overestimates the Fe3+/ΣFe value of mantle garnets (from xenoliths and megacrysts) for which Fe3+/ΣFe had been determined previously by Mössbauer spectroscopy. This is probably a result of differences in composition between the synthetic and natural garnets. For the mantle garnets, Fe3+/ΣFe is strongly correlated with the intensity ratio of post-edge features at 7138.4 and 7161.7 eV. The deviation of the Mössbauer results from a linear fit is less than 0.01 (1 σ). This suggests a new method for determining Fe3+/ΣFe from XANES spectra that does not require precise energy calibration or spectral fitting. The accuracy and precision for mantle garnets (within the compositional range studied: 0.75 ≤ Mg/(Mg + Fe) ≤ 0.86, 3.7–6.3 wt.% CaO, and 0.3–7.4 wt.% Cr2O3) is comparable to those of Mössbauer spectrosopy, however, XANES spectra can be acquired in ~ 15 min, allowing large numbers of samples to be analysed or the distribution of Fe3+/ΣFe to be mapped with micron spatial resolution. © 2010, Elsevier Ltd.en_AU
dc.identifier.citationBerry, A. J., Yaxley, G. M., Woodland, A. B., & Foran, G. J. (2010). XANES calibration for determining the oxidation state of iron in mantle garnet. Chemical Geology, 278(1-2), 31-37. doi:10.1016/j.chemgeo.2010.08.019en_AU
dc.identifier.govdoc3086en_AU
dc.identifier.issn0009-2541en_AU
dc.identifier.issue1-2en_AU
dc.identifier.journaltitleChemical Geologyen_AU
dc.identifier.pagination31-37en_AU
dc.identifier.urihttp://dx.doi.org/10.1016/j.chemgeo.2010.08.019en_AU
dc.identifier.urihttp://apo.ansto.gov.au/dspace/handle/10238/2884en_AU
dc.identifier.volume278en_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectGarnetsen_AU
dc.subjectIronen_AU
dc.subjectValenceen_AU
dc.subjectOxygenen_AU
dc.subjectAbsorptionen_AU
dc.subjectX-ray spectraen_AU
dc.titleXANES calibration for determining the oxidation state of iron in mantle garneten_AU
dc.typeJournal Articleen_AU
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