Abstract
AbstractWe 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 to laser‐driven shock compression. Shock compression induces a disordering of the crystalline structure evidenced by the appearance of a diffuse X‐ray diffraction signal at nanosecond timescales 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.
Highlights
The abundance of (Mg,Fe)SiO3 compounds in planetary mantles and the geochemical similarities between the Earth, enstatite‐rich chondrites (Boyet et al, 2018; Dauphas, 2017), and/or carbonaceous chondrites (Drake & Righter, 2002) requires an understanding of how space‐related processes affect these meteorites before falling on Earth
We 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 to laser‐driven shock compression
In order to understand transformation kinetics in shocked enstatite and to overcome the limitations inherent to the pressure‐density diagram, we investigate possible temperature differences between MgSiO3 enstatite shocked state formed in gas gun and in laser experiments
Summary
The abundance of (Mg,Fe)SiO3 compounds in planetary mantles and the geochemical similarities between the Earth, enstatite‐rich chondrites (Boyet et al, 2018; Dauphas, 2017), and/or carbonaceous chondrites (Drake & Righter, 2002) requires an understanding of how space‐related processes affect these meteorites before falling on Earth. In addition to space weathering and/or hydrous alteration, most meteorites have undergone multiple collisions and present evidence of shock metamorphism. These minerals can possess specific textures (e.g., mosaicism), amorphous material The acquisition of in situ structural data is required to identify the relevant microscopic mechanisms occurring during the different stages of the shock and their kinetics. This approach has long been prevented by technical limitations due to the short timescales involved in laser (nanosecond) and gas gun (microsecond) experiments
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