Kinetic vs. thermodynamic control of degassing of H2O-S ± Cl-bearing andesitic melts

The addition of >500 ppm Cl to the system slightly increased the S(fluid)/S(melt) under near-equilibrium conditions by a factor of ∼2 at QFM+1.8. Furthermore, Cl(fluid)/Cl(melt) (wt% Cl in fluid/wt% Cl in melt) showed a positive correlation with initial Cl content of the melt and ranged from 1 to 13, largely independent of r and tA. The interaction between S and Cl as well as the dependence of Cl(fluid)/Cl(melt) on Cl content in the melt may have a significant influence on S/Cl ratios in volcanic gasses.