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We determined the viscosity and heat capacity of a series of two basaltic liquids containing H2O, F, H2O + CO2, H2O + F, and H2O + CO2 + F. One was a natural calc-alkaline basalt from Fuego volcano, Guatemala, and the other was an Fe-free synthetic analog. The viscosity measurements were performed in the low-temperature, high-viscosity range (~ 109–1012 Pa s) just above the glass transition, where the kinetics of volatile exsolution are slow. Differential scanning calorimetry measurements were performed at atmospheric pressure from room temperature up to ~ 100 K above the glass transition. The water contents ranged from nominally anhydrous to 3 wt.% H2O, with F contents up to 2 wt.%, and CO2 contents up to 0.2 wt.%. Volatiles do not noticeably affect the heat capacity of glasses. The glass transition temperatures obtained from calorimetry and viscometry are in good agreement. Water has a strong viscosity-reducing effect on basaltic melts. F has a measurable viscosity-reducing effect in basaltic melts, but it is significantly smaller than that of water. The combined effects of H2O and F on viscosity appear to be additive on a wt.% basis. Both the effects of H2O and F on basaltic melts are smaller than those for more polymerized melts. Small quantities of CO2 do not measurably affect basaltic melt viscosity, at least in the presence of > 1 wt.% water. Future viscosity models incorporating fluorine need to account for the compositional dependence of its effects on dry and hydrous melts.
Robert G., Knipping J.L., Scherbarth S., Stechern A., Behrens H., 2015. Heat capacity and viscosity of basaltic melts with H2O ± F ± CO2. Chemical Geology 418, 51-65.
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