09:00 〜 10:30
[SIT17-P01] Al2O3 and H2O incorporation in MgSiO3 Akimotoite
キーワード：water, transition zone, lower mantle, Al content
Water plays important roles in the Earth, such as enhancing diffusion and lowering melting temperature of the mantle minerals, affecting the dynamics and evolution of the Earth’s interior. A previous study showing that ringwoodite in diamond inclusion can contain 1.5 wt% water suggesting that parts of the mantle transition zone have significant amounts of water, while below the transition zone bridgmanite and ferropericlase have very limited hydrogen storage. On the other hand, the depth of 660km seismic discontinuity increases near the subducted slab. At lower temperature, thus, water in the upper lower mantle may be stored in the phases of subducted slabs. Pyrolite or harzbergite forming the cold subducted slab probably contain considerable amounts of akimotoite together with ringwoodite and garnet. Knowledge of the stability field of hydrous akimotoite is useful to understand topography of the 660 km seismic discontinuity. Since akimotoite can incorporate certain amount of Al in its crystal structure. There is evidence showed that the Al2O3 incorporation affects on the water solubility of the hydrous phases and expand the stability field of hydrous phases.
In this study, we conducted high pressure and temperature experiments on MgSiO3-Al2O3 system under water saturated condition. The experiments have been performed at around 23GPa and 1200C-1600C using a Kawai type multianvil apparatus with standard 10-4 cell assembly, representing the pressure-temperature conditions of upper lower mantle.
At water saturated condition, we found that akimotoite is the main phase at 1400C and 1600C. There is no akimotoite found in 1200C run and phase D is the dominant phase. The results indicate that both alumina and water contents in these phases increase with increasing temperature under hydrous conditions possibly due to the strong Al3+-H+ charge coupling substitution. We will also report the effects of Al and water on the phase boundaries of akimotoite and bridgmanite.
In this study, we conducted high pressure and temperature experiments on MgSiO3-Al2O3 system under water saturated condition. The experiments have been performed at around 23GPa and 1200C-1600C using a Kawai type multianvil apparatus with standard 10-4 cell assembly, representing the pressure-temperature conditions of upper lower mantle.
At water saturated condition, we found that akimotoite is the main phase at 1400C and 1600C. There is no akimotoite found in 1200C run and phase D is the dominant phase. The results indicate that both alumina and water contents in these phases increase with increasing temperature under hydrous conditions possibly due to the strong Al3+-H+ charge coupling substitution. We will also report the effects of Al and water on the phase boundaries of akimotoite and bridgmanite.