Heavy δ57Fe in ocean island basalts: A non-unique signature of processes and source lithologies in the mantle

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dc.contributor.author Soderman, Caroline R.
dc.contributor.author Matthews, Simon
dc.contributor.author Shorttle, Oliver
dc.contributor.author Jackson, Matthew G.
dc.contributor.author Ruttor, Saskia
dc.contributor.author Nebel, Oliver
dc.contributor.author Turner, Simon
dc.contributor.author Beier, Christoph
dc.contributor.author Millet, Marc-Alban
dc.contributor.author Widom, Elisabeth
dc.contributor.author Humayun, Munir
dc.contributor.author Williams, Helen M.
dc.date.accessioned 2021-10-22T22:21:36Z
dc.date.available 2021-12-18T03:45:37Z
dc.date.issued 2021
dc.identifier.citation Soderman , C R , Matthews , S , Shorttle , O , Jackson , M G , Ruttor , S , Nebel , O , Turner , S , Beier , C , Millet , M-A , Widom , E , Humayun , M & Williams , H M 2021 , ' Heavy δ57Fe in ocean island basalts: A non-unique signature of processes and source lithologies in the mantle ' , Geochimica et Cosmochimica Acta , vol. 292 , pp. 309-332 . https://doi.org/10.1016/j.gca.2020.09.033
dc.identifier.other PURE: 149846726
dc.identifier.other PURE UUID: 79330248-87e6-4622-84bd-2964b0140c8e
dc.identifier.other RIS: urn:0F8B72976175C895B19F66C8D7C97521
dc.identifier.other WOS: 000590778600003
dc.identifier.other ORCID: /0000-0001-7014-7049/work/85118930
dc.identifier.uri http://hdl.handle.net/10138/335614
dc.description.abstract Lithological heterogeneity is a widely accepted feature of the Earth’s mantle, with recycled crustal material accounting for a significant part of heterogeneity in ocean island basalt (OIB) geochemistry. Fe isotopes have been used to link geochemical heterogeneity in OIB sources to distinct mantle lithologies due to their mineral-specific equilibrium fractionation effects, or their composition, such as incorporation of kinetically-fractionated core liquids entrained from the core-mantle boundary. Here we present Fe isotope data for Samoan shield, and Azores volcanoes, together with a combined phase-equilibria and equilibrium mineral-melt isotope fractionation model. These OIB lavas allow us to study the roles of core-derived and recycled mantle components in generating heavy δ57Fe melts. Heavy δ57Fe correlates with radiogenic isotope signatures of enrichment by a crustal component and not with Fe/Mn or any indicator of core involvement. However, single-stage melting of a MORB-like eclogitic pyroxenite cannot generate the heavy δ57Fe seen in Pitcairn, Azores, and rejuvenated Samoa lavas. Melts of a reaction-zone pyroxenite (commonly suggested to form part of the OIB source), derived from eclogite melts hybridised with peridotite, also fail to generate the heaviest Fe isotopic compositions seen in OIB. Instead, the generation of heavy δ57Fe melts in OIB requires: (1) processes that make subducted eclogite isotopically heavier than its pristine precursor MORB (e.g., hydrothermal alteration, metamorphism, sediment input); (2) lithospheric processing, such as remobilisation of previously frozen small-degree melts, or a contribution from lithospheric material metasomatised by silicate melts; and/or (3) melting conditions that limit the dilution of melts with heavy δ57Fe by ambient lower δ57Fe materials. No single process we consider can generate the heavy δ57Fe seen in the Azores, Pitcairn, and rejuvenated Samoan lavas. Therefore, it cannot be assumed that a pyroxenite lithology derived from recycled crustal material is the sole producer of heavy δ57Fe melts in OIB, nor can these signatures be related to contributions from the Earth’s core. Instead, the observation of heavy δ57Fe OIB melts cannot be ascribed to a unique source or process. This ambiguity reflects the multitude of processes operating from the generation of recycled lithologies through to their mantle melting: from MORB generation, its low temperature alteration, through mantle heterogeneity development and lithospheric processing, to eruption at ocean islands. en
dc.format.extent 24
dc.language.iso eng
dc.relation.ispartof Geochimica et Cosmochimica Acta
dc.rights cc_by_nc_nd
dc.rights.uri info:eu-repo/semantics/openAccess
dc.subject Iron isotopes
dc.subject Mantle heterogeneity
dc.subject Pyroxenite
dc.subject Mantle geochemistry
dc.subject Ocean island basalt
dc.subject 1171 Geosciences
dc.title Heavy δ57Fe in ocean island basalts: A non-unique signature of processes and source lithologies in the mantle en
dc.type Article
dc.contributor.organization Petrology and Geochemistry
dc.contributor.organization Department of Geosciences and Geography
dc.description.reviewstatus Peer reviewed
dc.relation.doi https://doi.org/10.1016/j.gca.2020.09.033
dc.relation.issn 0016-7037
dc.rights.accesslevel openAccess
dc.type.version acceptedVersion
dc.identifier.url http://www.sciencedirect.com/science/article/pii/S0016703720306050

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