Enthalpy of silicate melts from 1520 to 2600 K under ambient pressure. [Liquid SiO/sub 2/, CaSiO/sub 3/, and CaMgSi/sub 2/O/sub 6/]

We measured the enthalpy increments, H/sub T/-H/sub 298/, for liquid SiO/sub 2/, CaSiO/sub 3/, and CaMgSi/sub 2/O/sub 6/ over the temperature range 1700-2600 K. Experimental enthalpies for CaSiO/sub 3/ and CaMgSi/sub 2/O/sub 6/ are higher than estimates based on simple additivity by 15-20% at 2000 K. Heat capacities were independent of temperature. We calculated partial molal heat capacities for CaO and MgO liquids from the enthalpy data. We also measured the enthalpies of five polycomponent melts obtained by fusing various rocks collected from the Department of Energy Nevada Test Site; these were measured over the range 1520-2600 K. Two of these compositions showed a temperature trend in their heat capacities, indicating that models that assume temperature-independent partial molal heat capacities may be inadequate for estimating thermal properties of complex liquid silicates.