Nitrogen isotope fractionation during terrestrial core-mantle separation

Y. Li, B. Marty, S. Shcheka, L. Zimmermann, H. Keppler
2016 Geochemical Perspectives Letters  
doi: 10.7185/geochemlet.1614 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
more » ... the nitrogen isotope fractionation d 15 N metal-silicate is −3.5 ± 1.7 ‰. Calculations show that the bulk Earth is more depleted in d 15 N than the present-day mantle, and that the presentday mantle d 15 N 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 d 15 N values.
doi:10.7185/geochemlet.1614 fatcat:nbr7vgwxdvgpjk4h3yjhex36rq