Sulfur diffusion in basaltic melts

Abstract

We measured the diffusion coefficients of sulfur in two different basaltic melts at reduced conditions (i.e., in the sulfide stability field), temperatures from 1225°C to 1450°C, pressures of 0.5 and 1 GPa, and water concentrations of 0 and 3.5 wt%. Although each melt is characterized by slightly different sulfur diffusion coefficients, the results can be combined to create a general equation for sulfur diffusion in anhydrous basalts: D = 2.19 × 10 − 4 exp ⁡ ( − 226.3 ± 58.3 R T ) where D is the diffusion coefficient in m 2s -1, the activation energy is in kJ mol -1, R is the gas constant, and T is the temperature in K. Sulfur diffusion in basalts with 3.5 wt% water is a factor of three to seven higher than in anhydrous melts and can be described by: D = 5.91 × 10 − 7 exp ⁡ ( − 130.8 ± 82.6 R T ) At the conditions of this study the pressure does not measurably affect sulfur diffusion. Sulfur diffusion in dry basaltic melts is one order of magnitude higher than sulfur diffusion in dry andesitic and dacitic melts, whereas sulfur diffusion in hydrous basaltic and andesitic melts is within the same order of magnitude. When compared to the diffusivity of other volatile species in nominally dry basaltic melts, sulfur diffusion appears to be two times lower than CO 2 diffusion and two orders of magnitude lower than H 2O diffusion.