17:15 〜 18:45
[SIT15-P08] Effect of Al2O3 and H2O incorporation on the MgSiO3 Akimotoite-Bridgmanite Phase Boundary
キーワード：water, akimotoite, bridgmanite, lower mantle, phase boundary
Water plays important roles in the Earth, such as enhancing diffusion and lowering the melting temperature of the mantle minerals, affecting the dynamics and evolution of the Earth's interior. A previous study showed 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 temperatures, thus, water in the upper lower mantle may be stored in the phases of subducted slabs. Pyrolite or harzburgite
forming the cold subducted slab probably contains considerable amounts of
akimotoite together with ringwoodite and garnet. Knowledge of the stability field
of hydrous akimotoite is useful for understanding the topography of the 660 km seismic
discontinuity. Since akimotoite can incorporate a certain amount of Al in its crystal
structure. There is evidence showing that the Al2O3 incorporation affects the water solubility of the hydrous phases and expands the stability field of hydrous phases.
In this study, we conducted high-pressure and temperature experiments on the MgSiO3-Al2O3 system under both dry conditions and water-saturated conditions. The experiments have been performed at around 21-24GPa and 1200C -1600C using a Kawai type multi anvil apparatus with standard 10/4 cell assembly, representing the pressure temperature conditions of the upper lower mantle.
At water-saturated conditions, we found that there is no akimotoite found in the 1200C run, and phase D is the dominant phase. Akimotoite is the main phase when pressure is around 23GPa. The results also 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. At both dry and water-saturated conditions, we found alumina content can expand the stability field of akimotoite. The compared results also showed that water content can expand the stability field of akimotoite.
forming the cold subducted slab probably contains considerable amounts of
akimotoite together with ringwoodite and garnet. Knowledge of the stability field
of hydrous akimotoite is useful for understanding the topography of the 660 km seismic
discontinuity. Since akimotoite can incorporate a certain amount of Al in its crystal
structure. There is evidence showing that the Al2O3 incorporation affects the water solubility of the hydrous phases and expands the stability field of hydrous phases.
In this study, we conducted high-pressure and temperature experiments on the MgSiO3-Al2O3 system under both dry conditions and water-saturated conditions. The experiments have been performed at around 21-24GPa and 1200C -1600C using a Kawai type multi anvil apparatus with standard 10/4 cell assembly, representing the pressure temperature conditions of the upper lower mantle.
At water-saturated conditions, we found that there is no akimotoite found in the 1200C run, and phase D is the dominant phase. Akimotoite is the main phase when pressure is around 23GPa. The results also 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. At both dry and water-saturated conditions, we found alumina content can expand the stability field of akimotoite. The compared results also showed that water content can expand the stability field of akimotoite.