The sulfur oxidation transition in silicate magmas and its role in explosive volcanic hazards

The nature of sulfur in magmatic systems, particularly silicate melts, is an important control its ultimate behaviour and role in volcanic processes, being related to ore formation or volcanic outgassing. Recent spectroscopic developments using XANES allow the study of the variations in S-species present in natural and synthetic glasses. We will determine S oxidation states in key samples to elucidate the variations of S-speciation in volcanic melt compositions with different fO2 and temperatures to constrain the fO2 conditions for the transition from sulfide (S2-) to sulfate (S6+) in silicate melts. In addition, selected natural samples representative of arc magmas from Southeast Asia will be studied to quantify the abundances of key sulfur species. Our XANES data will enable us to constrain volatiles dissolved in magma, both during magma storage and during magma evolution when traveling through the magma conduit pre-eruption, linking sulfur to eruptive behaviour and magma dynamics.