[Abstract]

Advances in calorimetric measurements for magmatic liquids in the recent two decades are reviewed. This paper summarized previously reported values of heat capacities of silicate glasses and liquids and heats of fusion of minerals. Some of the values for heats of fusion are recalculated using the recently reported heats of vitrification and more reliable heat capacities of solids compared with those previously used. Heats of mixing of silicate liquids are also re-examined using excess enthalpies of glasses, heat capacities of end-members, excess heat capacities of liquids and recalculated values of heats of fusion. Excess enthalpies of pseudobinary silicate liquids are generally within +-30 kJ/mol and mostly +5~-10 kJ/mol. Although the excess enthalpies reach only 3-10 % of enthalpies of fusion, those cannot be ignored, because liquidus temperatures and compositions of minerals are greatly affected by small excess enthalpies. Based on the compilation of the excess enthalpies by direct and indirect measurements, we found that interactions among network-forming oxides (SiO2, NaAlO2, KAlO2), network-modifying oxides (CaO, MgO) and intermediate oxide (CaAl2O4) control the excess enthalpy of silicate liquid. As a preliminary test for generalized prediction of enthalpy of magmatic liquids, regular solution parameters for K2O-Na2O-CaO-MgO-Al2O3-SiO2 liquids are determined using compiled calorimetric enthalpies using a least square method. Finally, Adam-Gibbs theory for viscosity and configurational entropy of silicate liquid are reviewed. In order to express Gibbs free energy of magmatic liquids, the following studies will be required in future: (1) measurements of excess heat capacity by drop calorimetry for liquids including interactions between NaAlO2, KAlO2 and CaO, MgO, (2) measurements of excess enthalpy by solution calorimetry and relative enthalpy by drop calorimetry for Fe-bearing multicomponent glasses and liquids, and (3) determinations of entropy of mixing and configurational entropy by systematic viscosity measurements for multicomponent silicate liquids.

Key words:

magma, calorimetry, thermodynamics, silicate melt, enthalpy, entropy