High Temperature Thermochemistry Laboratory고온열화학연구실

Using experimental results at 1·0 GPa for the systems CaO–SiO₂, MgO–SiO₂, CaMgSi₂O₆–SiO₂ and CaMgSi₂O₆–Mg₂SiO₄, and all the currently available phase equilibria and thermodynamic data at 1 bar, we have optimized the thermodynamic properties of the liquid phase at 1·0 GPa. The new optimized thermodynamic parameters indicate that pressure has little effect on the topology of the CaO–SiO₂, CaMgSi₂O₆–SiO₂, and CaMgSi₂O₆–Mg₂SiO₄ systems but a pronounced one on the MgO–SiO₂ binary. The most striking change concerns passage of the MgSiO₃ phase from peritectic melting at 1 bar to eutectic melting at 1·0 GPa. This transition is estimated to occur at 0·41 GPa. For the CaMgSi₂O₆–SiO₂ and CaMgSi₂O₆–Mg₂SiO₄ pseudo-binaries, the size of the field clinopyroxene + liquid increases with increasing pressure. This change is related to the shift of the piercing points clinopyroxene + silica + liquid (from 0·375 mol fraction SiO₂ at 1 bar to 0·414 at 1·0 GPa) and clinopyroxene + olivine + liquid (from 0·191 mol fraction SiO₂ at 1 bar to 0·331 at 1·0 GPa) that bound the clinopyroxene + liquid field in the CaMgSi₂O₆·SiO₂ and CaMgSi₂O₆·Mg₂SiO₄ pseudo-binaries, respectively.