Structure and Properties of Albite Melt at High Pressures

Abstract

We have used first-principles molecular dynamics simulation to examine the high-pressure behavior of an aluminosilicate melt with albite stoichiometry (NaAlSi3O8). We have explored the equation of state and transport properties up to a pressure of 25 GPa and over a range of temperatures (2500–4000 K). Our results show that upon compression of up to 5 GPa, the initial densification in an albite melt occurs by the reduction of the T–O–T bond angle; however, the Si–O coordination remains virtually unchanged. Upon compression beyond 5 GPa, the densification occurs via changes in the T–O coordination. We also find that at lower isotherms, i.e., 2500–3000 K, the viscosity decreases upon compression and there is a concomitant enhancement of the diffusivity of the network-forming tetrahedral cations (silicon/aluminum) and oxygen anions. However, there is a reversal in the trend of viscosity and diffusivity upon further compression. For all of the temperatures explored in this study, at higher pressures, i.e., >10...