Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8915671 | Physics of the Earth and Planetary Interiors | 2018 | 34 Pages |
Abstract
Enthalpies of high-pressure phase transitons in ZrSiO4 were measured by high-temperature drop-solution calorimetry. The enthalpies for the zircon-reidite transition in ZrSiO4 and for dissociation of reidite to cotunnite-type ZrO2â¯+â¯SiO2 stishovite were obtained to be 27.5â¯Â±â¯3.3 and 50.3â¯Â±â¯3.0â¯kJ/mol, respetively, at 298â¯K. By thermal relaxation method, low-temperature isobaric heat capacities of ZrSiO4 reidite and cotunnite-type ZrO2 were measured, giving standard entropies at 298â¯K of 77.29â¯Â±â¯0.04 and 49.10â¯Â±â¯0.04â¯J/mol·K, respectively. Combining the measured enthalpies and entropies with other available thermophysical data, the transition boundaries in ZrSiO4 were calculated. The calculated zircon-reidite transiton boundary is consistent with that by in situ high-pressure expreiments by Ono et al. (2004a) within the errors. The calculated dissociation boundary of reidite has a smaller slope than that by high-pressure quench expreiments by Tange and Takahashi (2004). The equilibrium zircon-reidite transition pressure is calculated to be 8â¯GPa at 298â¯K, which is by 12-15â¯GPa lower than the transition pressures observed by room-temperature static compression experiments. Our results suggest that zircon transforms to reidite and dissociates into the two phases at 330 and 610â¯km depths, respectively, along the normal mantle geotherm. Combining the calculated phase relations with kinetics estimated from the first principles calculation may provide some insights to P, T conditions which reidites found in impact ejecta layers and craters experienced.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Geophysics
Authors
Masaki Akaogi, Saki Hashimoto, Hiroshi Kojitani,