Decaying shock studies of phase transitions in MgO-SiO2 systems: Implications for the super-Earths’ interiors

R. M. Bolis^1,2, G. Morard³, T. Vinci^1,2, A. Ravasio^1,2, E. Bambrink^1,2, M. Guarguaglini^1,2, M. Koenig^1,2,4, R. Musella⁵, F. Remus⁶, J. Bouchet⁶, N. Ozaki^7,8, K. Miyanishi⁸, T. Sekine⁹, Y. Sakawa¹⁰, T. Sano¹⁰, R. Kodama^4,7,8, F. Guyot³, and A. Benuzzi-Mounaix^1,2  Decaying shock studies of phase transitions in MgOSiO₂ systems: implications for the Super-Earths interiors. Geophys. Res. Lett., 43, 1–9.

1LULI - CNRS, Ecole Polytechnique, CEA, Université Paris-Saclay, F-91128 Palaiseau cedex, France,

2Sorbonne Universités,UPMC Univ Paris 06, CNRS, Laboratoire d’utilisation des lasers intenses (LULI), place Jussieu, 75252 Paris cedex 05, France,

3Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR CNRS 7590, Sorbonne Universités-Université Pierre et Marie Curie, CNRS, Muséum National d’Histoire Naturelle, IRD, Paris, France,

4Institute for Academic Initiatives,Osaka University, Suita, Japan,

5LUTH, Observatoire de Paris, CNRS, Université Paris Diderot, Meudon, France,

6CEA, DAM,DIF, Arpajon, France,

7Graduate School of Engineering, Osaka University, Suita, Japan,

8Photon Pioneers Center, OsakaUniversity, Suita, Japan,

9Department of Earth and Planetary Systems Science, Hiroshima University, Higashihiroshima,Japan,

10Institute of Laser Engineering, Osaka University, Suita, Japan

Abstract

We report an experimental study of the phase diagrams of MgO, MgSiO3, and Mg2SiO4 at high pressures. We measured the shock compression response, including pressure-temperature Hugoniot curves of MgO, MgSiO3, and Mg2SiO4 between 0.2–1.2 TPa, 0.12–0.5 TPa, and 0.2–0.85 TPa, respectively, using laser-driven decaying shocks. A melting signature has been observed in MgO at 0.47 ± 0.04 TPa and 9860 ± 810 K, while no such phase changes were observed either in MgSiO3 or in Mg2SiO4. Increases of reflectivity of MgO, MgSiO3, and Mg2SiO4 liquids have been detected above 0.55 TPa (12760 K), 0.15 TPa (7540 K), 0.2 TPa (5800 K), respectively. In contrast to SiO2, melting and metallization of these compounds do not coincide, implying the presence of poorly electrically conducting liquids close to the melting lines. This has important implications for the generation of dynamos in super-Earth’s mantles.

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070466/abstract