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A re-assessment of the oxidation state of iron in MORB glasses

Berry, Andrew; Stewart, Glen A.; O'Neill, Hugh; Mallmann, Guil; Mosselmans, J. F. W.

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The oxidation state of Fe, Fe/3+ΣFe (where ΣFe=Fe2++Fe3+), in glass samples of mid-ocean ridge basalt (MORB), from a wide range of localities, was determined by XANES spectroscopy to be 0.10(2) (n=42). This value is lower than that reported previously by XANES, 0.16(1) (n=103), but consistent with the most recent value determined by redox titrations, 0.11(2) (n=104), all for similar sets of samples. We attribute the anomalously high XANES value of 0.16 to a calibration error resulting from the...[Show more]

dc.contributor.authorBerry, Andrew
dc.contributor.authorStewart, Glen A.
dc.contributor.authorO'Neill, Hugh
dc.contributor.authorMallmann, Guil
dc.contributor.authorMosselmans, J. F. W.
dc.date.accessioned2021-05-12T23:42:18Z
dc.identifier.issn0012-821X
dc.identifier.urihttp://hdl.handle.net/1885/232983
dc.description.abstractThe oxidation state of Fe, Fe/3+ΣFe (where ΣFe=Fe2++Fe3+), in glass samples of mid-ocean ridge basalt (MORB), from a wide range of localities, was determined by XANES spectroscopy to be 0.10(2) (n=42). This value is lower than that reported previously by XANES, 0.16(1) (n=103), but consistent with the most recent value determined by redox titrations, 0.11(2) (n=104), all for similar sets of samples. We attribute the anomalously high XANES value of 0.16 to a calibration error resulting from the interpretation of Mössbauer spectra and the resulting Fe/3+ΣFe values of the standards. Our alternative interpretation removes the problem of resolving Fe/3+ΣFe values <∼0.1 in basaltic glasses, produces isomer shift and quadrupole splitting values for Fe3+ that are independent of Fe3+/ΣFe (as is the case for Fe2+), and gives Fe/3+ΣFe values that are consistent with the thermodynamically expected dependence on oxygen fugacity (fO2). Fe/3+Fe2+ is related to fO2 for our synthetic MORB composition by the temperature independent expression ΔQFM=4log⁡(Fe3+/Fe2+)+4.23(5), where ΔQFM is the fO2 in log units relative to the quartz–fayalite–magnetite buffer. The average fO2 of natural MORB was estimated to be QFM+0.1.
dc.description.sponsorshipA.J.B thanks the Australian Research Council for the award of a Future Fellowship (FT120100766).
dc.format.mimetypeapplication/pdf
dc.language.isoen_AU
dc.publisherElsevier
dc.rights© 2017 Elsevier B.V.
dc.sourceEarth and Planetary Science Letters
dc.subjectMössbauer spectroscopy
dc.subjectXANES spectroscopy
dc.subjectMORB
dc.subjectoxygen fugacity
dc.subjectFe3+/Fe2+
dc.titleA re-assessment of the oxidation state of iron in MORB glasses
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume483
dcterms.dateAccepted2017-11-14
dc.date.issued2018-02-01
local.identifier.absfor040312 - Structural Geology
local.identifier.absfor040503 - Physical Oceanography
local.identifier.ariespublicationa383154xPUB9217
local.publisher.urlhttps://www.sciencedirect.com/
local.type.statusPublished Version
local.contributor.affiliationBerry, Andrew, College of Science, ANU
local.contributor.affiliationStewart, Glen A, University of New South Wales
local.contributor.affiliationO'Neill, Hugh, College of Science, ANU
local.contributor.affiliationMallmann, Guil, College of Science, ANU
local.contributor.affiliationMosselmans, J. F. W., Harwell Science and Innovation Campus
local.description.embargo2099-12-31
dc.relationhttp://purl.org/au-research/grants/arc/FT120100766
local.bibliographicCitation.startpage114
local.bibliographicCitation.lastpage123
local.identifier.doi10.1016/j.epsl.2017.11.032
dc.date.updated2020-11-23T11:30:49Z
local.identifier.scopusID2-s2.0-85038420468
CollectionsANU Research Publications

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