[S-IT21] 核-マントルの相互作用と共進化

[SIT21-25] Low hydrogen contents in the cores of terrestrial planets

★Invited Papers

*Vincent Clesi¹、Mohamed Ali Bouhifd²、Nathalie Bolfan-Casanova²、Geeth Manthilake²、Federica Schiavi²、Caroline Raepsaet³、Hélène Bureau⁴、Hicham Khodja³、Denis Andrault² (1.Laboratoire de Geologie de Lyon - Terre, Planètes, Environnement, Université Claude Bernard Lyon 1, CNRS, ENS-Lyon, 69622 Villeurbanne, France.、2.Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS UMR 6524, OPGC–IRD, Campus Universitaire des Cézeaux, 6 Avenue Blaise Pascal, 63178 Aubière Cedex, France.、3.Laboratoire d’Etude des Eléments Légers, NIMBE, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif sur Yvette Cedex, France.、4.Institut de Minéralogie et de Physique de la Matière et de Cosmochimie, Sorbonne Universités, UMR CNRS-UPMC 7590, 4 place Jussieu, 75252 Paris, France.)

キーワード：Hydrogen, Core formation, Primitive Earth, Experimental Petrology

The accretion of planets from primordial materials and their subsequent differentiation to form a core and a mantle are fundamental questions in terrestrial and solar system. Many of the questions about the processes are still open and much debated. For example, could the presenceof water during the metallic phase segregation affect the planet-accretion models? The existing studies on the elemental metal-silicate partitioning under hydrous conditions were extended recently to a range of P, T, f_O2 and water content (5 - 20 GPa, 2000 - 2500 K, from 1 to 5 log units below the iron-wüstite buffer, and for Χ_H2O varying from 500 ppm to 1.5 wt%) [1]. These experimental results show that except for Fe, there is no effect of water on the partitioning of moderately siderophile elements. It allowed us to build consistent models of planetary accretion from reducing to oxidized conditions. Furthermore, for the range of water concentrations studied, there is no evidence of important hydrogen incorporation into planetary cores, thus making unlikely for hydrogen to be a major light element of the core as previsously assumed [2]. We report H metal-silicate partition coefficients of about 0.2, up to two orders of magnitude lower than reported previously, and indicative of lithophile behavior. Our results imply H content of ~60 ppm in the Earth and Martian cores [3].

[1] Clesi et al. (2016) Geochim. Cosmochim. Acta 192, 97-121.

[2] Okuchi, T. (1997) Science 278, 1781-1784.

[3] Clesi et al. (2018) Science Advances 4: e1701876