17:15 〜 18:30
[SMP26-P05] Structural study on the Ca2MgAl2Si4O14 composition melt under pressure
キーワード：マグマ、アルミノケイ酸塩、X線回折、分子動力学シミュレーション
Natural magmas are predominantly aluminosilicate in composition, and therefore the studies on structural properties of aluminosilicate under pressure is important for understanding the physical properties of magma at depth. The structure of the Di50An50 composition (Ca2MgAl2Si4O14) melt was studied by X-ray diffraction analysis and molecular dynamics simulations up to 7 GPa and 2200 K. The high pressure and temperature X-ray diffraction experiments were performed by MAX80 installed at AR-NE5C of PF, KEK. X-ray diffraction profiles were measured by energy dispersive X-ray diffractions method. The MD simulations were conducted with the MXDORTO code. The simulation system was composed of 2400 atoms.
Assuming the coordination number of Si is fixed to be four, we evaluated the coordination number of Al from the experimentally determined radial distribution function. It is increases to about five by 7 GPa. Increasing trend of the coordination number of Al with pressure is consistent with the results from the MD simulations. The FSDP of the structure factor shifts toward higher-Q side with increasing pressure, indicating shrinkage of intermediate range order by compression. The pressure dependence of the position of the FSDP changes around 4 GPa, showing intermediate range order does not change much above 4 GPa. Shrinkage of intermediate range order is thought to be correlated to the reorganization of TO4 networks. These structural changes in the Ca2MgAl2Si4O14 melt were considered to correspond to the physical properties, such as viscosity, of the basaltic magma under pressure.
Assuming the coordination number of Si is fixed to be four, we evaluated the coordination number of Al from the experimentally determined radial distribution function. It is increases to about five by 7 GPa. Increasing trend of the coordination number of Al with pressure is consistent with the results from the MD simulations. The FSDP of the structure factor shifts toward higher-Q side with increasing pressure, indicating shrinkage of intermediate range order by compression. The pressure dependence of the position of the FSDP changes around 4 GPa, showing intermediate range order does not change much above 4 GPa. Shrinkage of intermediate range order is thought to be correlated to the reorganization of TO4 networks. These structural changes in the Ca2MgAl2Si4O14 melt were considered to correspond to the physical properties, such as viscosity, of the basaltic magma under pressure.