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Redox control on nitrogen isotope fractionation during planetary core formation
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Number of Authors: 82019 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 116, no 29, p. 14485-14494Article in journal (Refereed) Published
Abstract [en]

The present-day nitrogen isotopic compositions of Earth's surficial (N-15-enriched) and deep reservoirs (N-15-depleted) differ significantly. This distribution can neither be explained by modern mantle degassing nor recycling via subduction zones. As the effect of planetary differentiation on the behavior of N isotopes is poorly understood, we experimentally determined N-isotopic fractionations during metal-silicate partitioning (analogous to planetary core formation) over a large range of oxygen fugacities (Delta IW -3.1 < logfO(2) <Delta IW -0.5, where Delta IW is the logarithmic difference between experimental oxygen fugacity [fO(2)] conditions and that imposed by the coexistence of iron and wustite) at 1 GPa and 1,400 degrees C. We developed an in situ analytical method to measure the N-elemental and -isotopic compositions of experimental run products composed of Fe-C-N metal alloys and basaltic melts. Our results show substantial N-isotopic fractionations between metal alloys and silicate glasses, i.e., from -257 +/- 22% to -49 +/- 1% over 3 log units of fO(2). These large fractionations under reduced conditions can be explained by the large difference between N bonding in metal alloys (Fe-N) and in silicate glasses (as molecular N-2 and NH complexes). We show that the delta N-15 value of the silicate mantle could have increased by similar to 20 parts per thousand during core formation due to N segregation into the core.

Place, publisher, year, edition, pages
2019. Vol. 116, no 29, p. 14485-14494
Keywords [en]
nitrogen isotopes, fractionation, core formation, speciation, ion probe
National Category
Geochemistry Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:su:diva-171729DOI: 10.1073/pnas.1820719116ISI: 000475610000019PubMedID: 31262822OAI: oai:DiVA.org:su-171729DiVA, id: diva2:1350037
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-12-03Bibliographically approved

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Dalou, CeliaDeligny, CécilePiani, LauretteEdén, Mattias
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Department of Materials and Environmental Chemistry (MMK)
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Proceedings of the National Academy of Sciences of the United States of America
GeochemistryMetallurgy and Metallic Materials

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