Sulfur isotopes in magmatic hydrothermal systems, melts and magmas

Chapter 14, by Marini et al. (2011, this volume), reviews how the stable isotopes of sulfur serve as an important geochemical tool for the study of processes occurring in magma-related, hydrothermal systems, melts, and magmas. Sulfur has four stable isotopes with natural abundances of 95.02% (32S), 0.75% (33S), 4.21% (34S), and 0.02% (36S). Importantly, small variations in the ratios of these isotopes can be induced by kinetic and thermodynamic effects, and these variations or fractionations are exacerbated given the multiple oxidation states of sulfur. The fractionation of sulfur isotopes between co-existing phases is particularly large when the oxidation state of sulfur differs in both phases and when the phases have different aggregate physical states (i.e., gas phases vs. condensed phases). This chapter summarizes how sulfur isotopes have been measured in volcanic gases as well as in samples from magmatic rocks and or magmatic ore deposits. These data are compared with theoretical models of degassing and the crystallization and physical separation of sulfides and anhydrite from melt to gain insights into the processes occurring in magma chambers and during the ascent of the magma to the surface. In particular, this chapter addresses sulfur isotope characteristics for magmas and eruptive products of Mt. Vesuvius, Mt. Mazama, and Mt. Etna