Heat capacity and viscosity of basaltic melts with H2O±F±CO2 (original) (raw)

Thermochemistry and melting properties of basalt

Contributions to Mineralogy and Petrology, 2007

The heat capacities of the liquid, glassy and crystalline phases of an alkali basalt have been determined from relative enthalpies measured between 400 and 1,800 K. Values given by available models of calculation generally agree to within 2% of these results. As derived from the new data and the enthalpy of vitrification measured at 973 K by oxide-melt drop solution calorimetry for the same sample, the enthalpy of fusion of this basalt increases from 15.4 kJ/mol at 1,000 K to 33.6 kJ/mol at 1,800 K. Comparisons be-tween the enthalpies of fusion of basalt and model compositions confirm the small magnitude of the enthalpy of mixing between the molten mineral components of the liquids. Minor variations in the chemical composition have only a small effect in the heat capacity and the enthalpy of melting of basalt. The enthalpies of formation at 298 K from the oxides of the crystallized and glass phases of this alkali basalt are -112.2 and -98.5 kJ/mol, respectively, for a gram formula weight based on one mole of oxide components. Communicated by J. Hoefs. M. A. Bouhifd Á P. Richet Physique des Miné raux et des Magmas, IPGP,

The effect of H2O on the olivine liquidus of basaltic melts: experiments and thermodynamic models

Contributions to Mineralogy and Petrology, 2007

We designed and carried out experiments to investigate the effect of H 2 O on the liquidus temperature of olivine-saturated primitive melts. The effect of H 2 O was isolated from other influences by experimentally determining the liquidus temperatures of the same melt composition with various amounts of H 2 O added. Experimental data indicate that the effect of H 2 O does not depend on pressure or melt composition in the basaltic compositional range. The influence of H 2 O on melting point lowering can be described as a polynomial function C melt H 2 O in wt% : DT C ð Þ ¼ 40:4 C melt H 2 O À 2:97 C melt H 2 O 2 þ 0:0761 C melt H 2 O 3 : This expression can be used to account for the effect of H 2 O on olivine-melt thermometers, and can be incorporated into fractionation models for primitive basalts. The non-linear effect of H 2 O indicates that incorporation of H 2 O in silicate melts is non-ideal, and involves interaction between H 2 O and other melt components. The simple speciation approach that seems to account for the influence of H 2 O in simple systems (albite-H 2 O, diopside-H 2 O) fails to describe the mixing behavior of H 2 O in multi-component silicate melts. However, a non-ideal solution model that treats the effect of H 2 O addition as a positive excess free energy can be fitted to describe the effect of melting point lowering.

Heat capacity of hydrous basaltic glasses and liquids

Journal of Non-Crystalline Solids, 2014

We determined the heat capacities of four series of glasses and liquids of basaltic and basaltic andesite compositions from remelted volcanic rock samples and Fe-free synthetic analogues. The samples are low-alkali, Ca-and Mg-rich aluminosilicates with non-bridging oxygen to tetrahedrally-coordinated cation ratios (NBO/T) ranging between 0.33 and 0.67. Differential scanning calorimetry measurements were performed at atmospheric pressure between room temperature and~100 K above the glass transition for hydrous samples and up to~1800 K for dry samples. The water contents investigated range up to 5.34 wt.% (16.4 mol%). Water does not measurably affect the heat capacity of glasses. We derived a new value of the partial molar heat capacity of water in silicate glasses of C glass P;H2O ¼ 82:804 þ 10 −3 T−48:274 Â 10 −5 T −2 (J/mol K) using our new data in combination with literature data on more and less polymerized compositions. The increase in heat capacity at the glass transition is of the order of~30-40% and generally increases with increasing water content. The onset of the glass transition in hydrous samples occurs below the Dulong-Petit limit of 3R/g atom. The configurational heat capacity, i.e., the magnitude of the change in heat capacity observed at the glass transition, generally increases as polymerization decreases and as water content increases. We obtained a partial molar heat capacity of water in silicate liquids of basaltic composition of~86 J/mol K. This value is comparable to the partial molar values for the major oxides which range from~79 to 230 J/mol K. The partial molar heat capacity of water in silicate liquids appears to be compositionally-dependent, increasing as melt polymerization decreases. Such a dependence is certainly linked to the speciation and structural roles of water in complex silicate melts, however, a single value of~93 J/mol K could reproduce the heat capacity of hydrous liquids of a wide range of NBO/T (0-1.51) at temperatures up tõ 100 K above the glass transition and water contents of 0-3.76 wt.% with a root-mean square deviation of only 3.23 J/mol K.