Fe–FeO and Fe–Fe3C melting relations at Earth's core–mantle boundary conditions: Implications for a volatile-rich or oxygen-rich core

G.Morard a,∗, D.Andrault b, D.Antonangeli a, Y.Nakajima c,d, A.L.Auzende a,e, E.Boulard f, S.Cervera a, A.Clark a, O.T.Lord g, J.Siebert h, V.Svitlyk i, G.Garbarino i, M.Mezouar i
aInstitut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités – UPMC, UMR CNRS, 7590, Muséum National d’Histoire Naturelle, IRD UMR 206, F-75005 Paris, France
bLaboratoire Magmas et Volcans, CNRS-OPGC-IRD, Université Blaise Pascal, Clermont-Ferrand, France
cMaterials Dynamics Laboratory, RIKEN SPring-8 Center, RIKEN, Hyogo 679-5148, Japan
dDepartment of Physics, Kumamoto University, Kumamoto 860-8555, Japan
eUniv. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, ISTerre, F-38000 Grenoble, France
fSynchrotron Soleil, L’Orme des Merisiers, Saint Aubin, France
gSchool of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, UK
hInstitut de Physique du Globe de Paris, Université Paris 7, F-75005 Paris, France
iEuropean Synchrotron Radiation Facility, Grenoble, France

Eutectic melting temperatures in the Fe–FeO and Fe–Fe₃C systems have been determined up to 150 GPa. Melting criteria include observation of a diffuse scattering signal by in situ X-Ray diffraction, and textural characterisation of recovered samples. In addition, compositions of eutectic liquids have been established by combining in situ Rietveld analyses with ex situ chemical analyses. Gathering these new results together with previous reports on Fe–S and Fe–Si systems allow us to discuss the specific effect of each light element (Si, S, O, C) on the melting properties of the outer core. Crystallization temperatures of Si-rich core compositional models are too high to be compatible with the absence of extensive mantle melting at the core–mantle boundary (CMB) and significant amounts of volatile elements such as S and/or C (>5 at%, corresponding to >2 wt%), or a large amount of O (>15 at% corresponding to ∼5 wt%) are required to reduce the crystallisation temperature of the core material below that of a peridotitic lower mantle.

http://www.sciencedirect.com/science/article/pii/S0012821X1730290X