The theory of associated solutions provides a simple but rigorous framework for the use of speciation reactions to model nonideal mixing behavior of silicate melt components. Application of the theory to the system Ab-Qz-H2O requires only P-T solidus data in the anhydrous and HrO-saturated systems Ab-H2O and Ab-Qz-H2O to calibrate equilibrium constants of proposed modeling reactions. Because compositional data are not used in the calibration, agreement between predicted eutectic compositions and experimental data is a critical means of testing proposed model reactions. Investigation of the systems Ab-H2O and Ab-Qz-H2O indicates that if a modeling reaction producing a sodium silicate species is considered, neither interaction between albite and silica melt to produce new complexes nor nonideal mixing of species is required and agreement between predicted and experimental eutectic compositions can be obtained by considering only disproportionation in albite melts. The thermodynamic consequence of these assumptions is that the Ab and Qz melt components mix ideally, in agreement with available calorimetric data and in contrast with the results of Burnham and Nekvasil (1986). Use of alternate reactions (e.g., a jadeite-producing reaction) results in more complex mixing relations and discordant predicted compositions.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.