[S-MP23] Physics and Chemistry of Minerals

[SMP23-07] Amorphization mechanism and kinetics of high-pressure structures of SiO₂ in shocked meteorites

Miyuu Soejima¹, *Masayuki Nishi¹, Yuki Mori², Masakazu Ohno¹, Takumi Miura¹, Ryo Tsuruoka¹, Shogo Kawaguchi², Toru Shinmei³, Tatsuhiro Sakaiya¹, Tadashi Kondo¹ (1.Department of Earth and Space Science, Osaka University, 2.Japan Synchrotron Radiation Research Institute, 3.Geodynamics Research Center, Ehime University)

Keywords:Shocked meteorite, stishovite, seifertite, amorphization

High-pressure minerals found in shocked meteorites provide pressure–temperature–time information that can be used to constrain the impact histories of their parent bodies. On the other hand, the high remnant temperature after decompression (i.e., the post-shock temperature) often destroys high-pressure phases through back-transition or amorphization under a metastable state at ambient pressure. We recently investigated the amorphization mechanisms and kinetics of polycrystalline bridgmanite, concluding that the survival bridgmanite requires a residual temperature of 700 K.
In this study, the amorphization mechanisms and kinetics of stishovite and seifertite were investigated via time-resolved synchrotron XRD measurement at beamline BL02B2, SPring-8, Japan. The temperature was controlled using an N₂ gas blower. Amorphization of stishovite at temperatures above 850 K induced a decrease in XRD peak intensities. We found that significant volume expansion due to amorphization induced static stress, which prevented further amorphization. based on our experimental results, if 50% of stishovite remains crystalline, the post-shock temperature conditions can be estimated to be 900 K, assuming annealing time of 10³ s.