12:00 PM - 1:00 PM
Fluids exsolved from mafic melts are thought to be prevalently CO2-H2O ± S fluids. The concentration of H2O exsolved in these fluids controls the explosivity of volcanic eruptions and ore formation. Curiously, although CO2 and S have been reported and quantified in bubbles of mafic melt inclusions (MI) hosted in olivine, direct evidence of H2O exsolution into vapor bubbles has not been reported (although sometimes assumed). In this study, we reheated olivine-hosted MI from Mt. Somma-Vesuvius, and quenched the MI to a bubble-bearing glassy state. We report evidence that volatiles exsolved from melts in MI may consist predominantly of H2O. These results allow direct characterization of magmatic fluids exsolved from melts at depth beneath volcanoes, and corroborate solubility-model predictions that fluids exsolved from mafic melts may consist predominantly of H2O, with subordinate CO2.