Experimental investigation and optimization of thermodynamic properties and phase diagrams in the systems CaO-SiO2, MgO-SiO2, CaMgSi2O6-SiO2 and CaMgSi2O6-Mg2SiO4 to 1•0 GPa

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.