Implications of Laser-Driven Shock Experiments for the Core-Mantle Boundary

New techniques using laser-driven shock waves reveal the pressure - temperature conditions at which mantle rocks (silicates and oxides) become metallic fluids, hence core-like constituents. Experiments reaching peak pressures and temperatures of about 700 GPa (7 Mbar) and 3 x 104 K (3 eV) allow interpolation with lower-pressure measurements to reveal the properties of MgO, MgSiO3 and SiO2 at conditions of deep planetary interiors. We document shock-induced melting of MgO (14,970 ± 300 K at 470 ± 10 GPa) and MgSiO3 (7740 ± 450 K at 275 ± 10 GPa), and confirm previous findings for SiO2 (melting at 5620 ± 450 K at 116 ± 10 GPa), by monitoring temperature as a function of time for each sample as it is compressed by a strong but decaying shock wave. The melts show evidence of reflectivity > 20% at visible wavelengths, implying metallization ('ionization') of these oxides through the combined effects of pressure and temperature. These results indicate a blurring of the distinction between silicate and metallic constituents at the core-mantle boundary, particularly at the high temperatures immediately following a late-stage giant (Moon-forming) impact.