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Article Dans Une Revue Geochemical Perspectives Letters Année : 2016

Nitrogen isotope fractionation during terrestrial core-mantle separation

Résumé

The origin and evolution of the terrestrial nitrogen remains largely unresolved. In order to understand the potential influence of core-mantle separation on terrestrial nitrogen evolution , experiments were performed at 1.5 to 7.0 GPa and 1600 to 1800 °C to study nitrogen isotope fractionation between coexisting liquid Fe-rich metal and silicate melt. The results show that the metal/silicate partition coefficient of nitrogen D N metal/silicate ranges from 1 to 150 and the nitrogen isotope fractionation δ^15N metal–silicate is −3.5 ± 1.7 ‰. Calculations show that the bulk Earth is more depleted in δ^15N than the present-day mantle, and that the present-day mantle δ^15N of −5 ‰ could be derived from an enstatite chondrite composition via terrestrial core-mantle separation, with or without the addition of carbonaceous chondrites. These results strongly support the notion that enstatite chondrites may be a main component from which the Earth formed and a main source of the terrestrial nitrogen. Moreover, in the deep reduced mantle, the Fe-rich metal phase may store most of the nitrogen, and partial melting of the coexisting silicates may generate oceanic island basalts (OIBs) with slightly positive δ^15N values.

Domaines

Géochimie
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Dates et versions

hal-01346007 , version 1 (20-07-2016)

Identifiants

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Yan-Fu Li, B Marty, S Shcheka, L Zimmermann, H Keppler. Nitrogen isotope fractionation during terrestrial core-mantle separation. Geochemical Perspectives Letters, 2016, 2, pp.138-147. ⟨10.7185/geochemlet.1614⟩. ⟨hal-01346007⟩
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