15:45 〜 16:00
[U04-08] Time-resolved synchrotron X-ray observations of mineral transformations under static pressures: applications to non-equilibrium behaviors in shocked meteorites
★Invited Papers
High-pressure transformations occur on timescales of ~0.01 to a few seconds in shocked meteorites. Reactions in such short timescales often remain incomplete and/or metastable state, which is usually problematic for the interpretation, but can be good information for shock durations if the kinetics is experimentally known. Here we present some experimental results on curious kinetic behaviors in seifertite and lingunite, those presences in shocked meteorites have been difficult to explain based on phase equilibrium. A conventional method combining multi-anvil high-pressure apparatus with synchrotron white X-ray was routinely used to observe non-equilibrium behaviors and their kinetics in minerals at pressures up to ~30 GPa by collecting time-resolved X-ray diffraction data every 10 sec with energy dispersive method. By using this system, we found that seifertite and lingunite are metastably formed at high pressures from silica and plagioclase, respectively. The problematic presence of these phases in shocked meteorites can be reasonably explained as metastable phases. Extrapolations of kinetic data obtained to shorter timescales at higher temperatures of shock events uniquely constrain the critical shock durations and the size of the impactor. Similar strategy has also been applied to the back-transformation recorded in shocked meteorites. Time-resolved X-ray observations have revealed that some high-pressure phases such as bridgmanite and lingunite do not directly transform to their low-pressure phases, but through the amorphous state. This may explain the presence of amorphous phases with enstatite and plagioclase compositions in shocked meteorites. Our studies demonstrate that the conventional 10-second time-resolved synchrotron X-ray observations under static pressures capture the critical processes of solid-state reactions during shock events. On the other hand, crystallization of high-pressure phases from shock-induced melt is another important process to be solved. Improvement of the system with better time resolution and grain observations by 2D detector are required to detect the rapid melt crystallization processes.