title: Curious kinetic behavior in silica polymorphs solves seifertite puzzle in shocked meteorite.
abstract: The presence of seifertite, one of the high-pressure polymorphs of silica, in achondritic shocked meteorites has been problematic because this phase is thermodynamically stable at more than ~100 GPa, unrealistically high-pressure conditions for the shock events in the early solar system. We conducted in situ x-ray diffraction measurements at high pressure and temperatures, and found that it metastably appears down to ~11 GPa owing to the clear difference in kinetics between the metastable seifertite and stable stishovite formations. The temperature-insensitive but time-sensitive kinetics for the formation of seifertite uniquely constrains that the critical shock duration and size of the impactor on differentiated parental bodies are at least ~0.01 s and ~50 to 100 m, respectively, from the presence of seifertite.
authors.affiliation: Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Kubo
authors.affiliation: Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kato
authors.affiliation: Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Higo
authors.affiliation: Japan Synchrotron Radiation Research Institute, Hyogo 679-5198, Japan.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Funakoshi
keywords: high pressure; kinetics; metastable phase; seifertite; shocked meteorite; silica polymorphs