Decaying shock studies of phase transitions in MgO‐SiO 2 systems: Implications for the super‐Earths' interiors

• Published in: Geophysical research letters 2016-09, Vol.43 (18), p.9475-9483
• Main Authors: Bolis, R. M., Morard, G., Vinci, T., Ravasio, A., Bambrink, E., Guarguaglini, M., Koenig, M., Musella, R., Remus, F., Bouchet, J., Ozaki, N., Miyanishi, K., Sekine, T., Sakawa, Y., Sano, T., Kodama, R., Guyot, F., Benuzzi‐Mounaix, A.
• Format: Article
• Language: English
• Subjects: Astrophysics; Physics; Sciences of the Universe
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL070466

We report an experimental study of the phase diagrams of MgO, MgSiO 3 , and Mg 2 SiO 4 at high pressures. We measured the shock compression response, including pressure‐temperature Hugoniot curves of MgO, MgSiO 3 , and Mg 2 SiO 4 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 MgSiO 3 or in Mg 2 SiO 4 . Increases of reflectivity of MgO, MgSiO 3 , and Mg 2 SiO 4 liquids have been detected above 0.55 TPa (12760 K), 0.15 TPa (7540 K), 0.2 TPa (5800 K), respectively. In contrast to SiO 2 , 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. Magnesium oxides phase diagrams investigated along the Hugoniots between 0.2 and 1.2 TPa with decaying shocks and optical diagnostics New MgO experimental melting point proposed at 0.47 ± 0.04 TPa and 9860 ± 810 K No evidences of phase transition have been found for MgSiO 3 and Mg 2 SiO 4 between 0.12–0.5 TPa and 0.2–0.85 TPa, respectively