[P-CG22] Shock responses of planetary materials elucidated from meteorites and dynamic compression experiments

[PCG22-04] Linking occurrence and texture of dense silicate minerals in shocked meteorites with laser-shock experimental results of Mg₂SiO₄ analyzed by XFEL probe

*Takuo Okuchi¹, Narangoo Purevjav¹, Norimasa Ozaki², Takeshi Matsuoka², Yusuke Seto³, Yoshinori Tange⁴, Toshinori Yabuuchi⁵, Naotaka Tomioka⁶, Toshimori Sekine⁷, Ryosuke Kodama² (1.Institute for Planetary Materials, Okayama University, 2.Graduate School of Engineering, Osaka University, 3.Graduate School of Science, Kobe University, 4.Japan Synchrotron Radiation Research Institute, 5.RIKEN Harima Branch, 6.Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, 7.Center for High Pressure Science and Technology Advanced Research)

Keywords:dense silicate minerals, laser shock experiments, shock metamorphism, Mg2SiO4

Primitive meteorites often show features of shock metamorphism, including occurrences of dense polymorphs of major mineral phases. By previous transmission electron microscopy studies it was demonstrated that olivine (alpha-Mg₂SiO₄) often had transformed into its denser polymorphs such as ringwoodite (gamma-Mg₂SiO₄), and as a recently-discovered new structure (epsilon-Mg₂SiO₄: Tomioka and Okuchi, Sci. Rep. 2017). The impact events that produced these polymorphs played essential roles in the history of early solar system evolution. Here we tried to reproduce such a dynamic transformation process starting from forsterite olivine single crystals by using very strong laser beam and x-ray free electron laser (XFEL) beam in combination at SACLA, SPring-8, Japan. A transformation process has been successfully observed with sub-nanosecond resolution by x-ray diffraction using femtosecond XFEL pulses. We discovered an ultrafast transformation process completing only within few nanoseconds, which was not expected to occur during shock metamorphism of meteorites. It can be a shear-induced fast lattice slipping proceeding without any atomic diffusion process. We conclude that formation processes and environments of some of dense Mg₂SiO₄ polymorphs in heavily shocked meteorites are needed to be reconsidered to involve this fast process.