Direct observation of shock-induced disordering of enstatite below the melting temperature

International audienceWe report in situ structural measurements of shock-compressed single crystal orthoenstatite up to 337±55 GPa on the Hugoniot, obtained by coupling ultrafast X-ray diffraction (XRD) to laser-driven shock-compression. Shock compression induces a disordering of the crystalline structure evidenced by the appearance of a diffuse XRD signal at nanosecond time scales at 80±13 GPa on the Hugoniot, well below the equilibrium melting pressure (> 170 GPa). The formation of bridgmanite and post-perovskite have been indirectly reported in microsecond-scale plate-impact experiments. Therefore, we interpret the high-pressure disordered state we observed at nanosecond-scale as an intermediate structure from which bridgmanite and post-perovskite crystallize at longer timescales. This evidence of a disordered structure of MgSiO3 on the Hugoniot indicates that the degree of polymerization of silicates is a key parameter to constrain the actual thermodynamics of shocks in natural environments