Curious kinetic behavior in silica polymorphs solves seifertite puzzle in shocked meteorite

Tomoaki Kubo, Takumi Kato, Yuji Higo, Ken-ichi Funakoshi

Science Advances 08 May 2015:
Vol. 1 no. 4 e1500075
DOI: 10.1126/sciadv.1500075

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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.