Molecular Dynamics Simulations of the Anorthite-Water System Under Extreme Conditions

Incorporation of water plays an important role in modifying the physical and chemical properties of silicate melts. Water reacts with the melt constituents causing depolymerization and reduces the viscosity of the melt which directly impacts the eruptive power of magmas and the transfer of mass in magmatic processes. Anorthite is a Ca-bearing aluminosilicate having the chemical formula CaAl₂Si₂O₈. It is an end member of the feldspar series and an important constituent of the rocks comprising the Earth’s crust. We have made large simulation-cell molecular dynamics calculations in order to develop a detailed quantitative structural analysis of an hydrous anorthite melt system. ReaxFF reactive force fields are utilized to simulate the reaction between an anorthite melt and water at extreme temperatures. An analysis of bond lengths, pair correlations and bond angles within the hydrous melt is being made in order to determine how the structural properties of the system change under the extremes of pressure and temperature. The extent of depolymerization of the hydrous aluminosilicate melt, as determined from the transformation of Si – O – Si, Si – O – Al, and Al – O – Al bonds into terminating, non-bridging Si – OH and Al – OH bonds, will be discussed.