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dc.contributor.authorShorttle, Oliveren
dc.contributor.authorMoussallam, Yvesen
dc.contributor.authorHartley, Margareten
dc.contributor.authorMaclennan, Johnen
dc.contributor.authorEdmonds, Marieen
dc.contributor.authorMurton, Bramleyen
dc.date.accessioned2015-07-14T14:17:09Z
dc.date.available2015-07-14T14:17:09Z
dc.date.issued2015-07-25en
dc.identifier.citationEarth and Planetary Science Letters 2015, 427: 272–285. doi: 10.1016/j.epsl.2015.07.017
dc.identifier.issn0012-821X
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/248945
dc.description.abstractThe cycling of material from Earth's surface environment into its interior can couple mantle oxidation state to the evolution of the oceans and atmosphere. A major uncertainty in this exchange is whether altered oceanic crust entering subduction zones can carry the oxidised signal it inherits during alteration at the ridge into the deep mantle for long-term storage. Recycled oceanic crust may be entrained into mantle upwellings and melt under ocean islands, creating the potential for basalt chemistry to constrain solid Earth–hydrosphere redox coupling. Numerous independent observations suggest that Iceland contains a significant recycled oceanic crustal component, making it an ideal locality to investigate links between redox proxies and geochemical indices of enrichment. We have interrogated the elemental, isotope and redox geochemistry of basalts from the Reykjanes Ridge, which forms a 700 km transect of the Iceland plume. Over this distance, geophysical and geochemical tracers of plume influence vary dramatically, with the basalts recording both long- and short-wavelength heterogeneity in the Iceland plume. We present new high-precision Fe-XANES measurements of Fe³⁺/∑Fe on a suite of 64 basalt glasses from the Reykjanes Ridge. These basalts exhibit positive correlations between Fe³⁺/∑Fe and trace element and isotopic signals of enrichment, and become progressively oxidised towards Iceland: fractionation-corrected Fe³⁺/∑Fe increases by ∼0.015 and ΔQFM by ∼0.2 log units. We rule out a role for sulfur degassing in creating this trend, and by considering various redox melting processes and metasomatic source enrichment mechanisms, conclude that an intrinsically oxidised component within the Icelandic mantle is required. Given the previous evidence for entrained oceanic crustal material within the Iceland plume, we consider this the most plausible carrier of the oxidised signal. To determine the ferric iron content of the recycled component ([Fe₂O₃]) we project observed liquid compositions to an estimate of Fe₂O₃ in the pure enriched endmember melt, and then apply simple fractional melting models, considering lherzolitic and pyroxenitic source mineralogies, to estimate [Fe₂O₃] content. Propagating uncertainty through these steps, we obtain a range of [Fe₂O₃] for the enriched melts (0.9–1.4 wt%) that is significantly greater than the ferric iron content of typical upper mantle lherzolites. This range of ferric iron contents is consistent with a hybridised lherzolite–basalt (pyroxenite) mantle component. The oxidised signal in enriched Icelandic basalts is therefore potential evidence for seafloor–hydrosphere interaction having oxidised ancient mid-ocean ridge crust, generating a return flux of oxygen into the deep mantle.
dc.description.sponsorshipOS was supported by a Title A Fellowship from Trinity College, JM through NERC grant NE/J021539/1 and MH acknowledges a Junior Research Fellowship from Murray Edwards College, Cambridge. We acknowledge Diamond Light Source for time on beamline I18 under proposals SP9446, SP9456 and SP12130 and the support during our analytical sessions from beamline scientist Konstantin Ignatyev and principal beamline scientist Fred Mosselmans. The Smithsonian Institution National Museum of Natural History is thanked for their loan of NMNH 117393.
dc.languageEnglishen
dc.language.isoenen
dc.publisherElsevier
dc.rightsCreative Commons Attribution 4.0*
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/*
dc.subjectMantle fO₂en
dc.subjectXANESen
dc.subjectOxygenen
dc.subjectMantle heterogeneityen
dc.subjectpyroxeniteen
dc.titleFe-XANES analyses of Reykjanes Ridge basalts: Implications for oceanic crust's role in the solid Earth oxygen cycleen
dc.typeArticle
dc.description.versionThis is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.epsl.2015.07.017en
prism.endingPage285
prism.publicationDate2015en
prism.publicationNameEarth and Planetary Science Lettersen
prism.startingPage272
prism.volume427en
dc.rioxxterms.funderNERC
dc.rioxxterms.projectidNE/J021539/1
rioxxterms.versionofrecord10.1016/j.epsl.2015.07.017en
rioxxterms.licenseref.urihttp://www.rioxx.net/licenses/all-rights-reserveden
rioxxterms.licenseref.startdate2015-07-25en
dc.contributor.orcidShorttle, Oliver [0000-0002-8713-1446]
dc.contributor.orcidMoussallam, Yves [0000-0002-4707-8943]
dc.contributor.orcidMaclennan, John [0000-0001-6857-9600]
dc.contributor.orcidEdmonds, Marie [0000-0003-1243-137X]
dc.identifier.eissn1385-013X
rioxxterms.typeJournal Article/Reviewen
pubs.funder-project-idNERC (NE/J021539/1)


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Creative Commons Attribution 4.0
Except where otherwise noted, this item's licence is described as Creative Commons Attribution 4.0