1 GSA DATA REPOSITORY 2014260 “Effects of temperature, sulfur, and oxygen fugacity on the composition of sphalerite from submarine hydrothermal vents” Manuel Keith, Karsten M. Haase, Ulrich Schwarz-Schampera, Reiner Klemd, Sven Petersen, and Wolfgang Bach Methods A total of 12 polished sections and thin sections were petrographically examined prior to the geochemical analysis in order to identify the different mineral phases and to avoid effects of mineral inclusions. For this purpose the back-scattered electron mode of the electron probe microanalyzer has also been used. A total amount of 200 representative analyses were carried out by the electron microprobe analysis (Table DR2). The major and minor element composition of sphalerite was determined by electron microprobe analysis using a JEOL JXA-8200 Superprobe at the GeoZentrum Nordbayern. The quantitative analysis was carried out in an evacuated chamber (<4.3 x 10 -6 mbar) with a focused beam, an acceleration voltage of 20 kV, and a beam current of 20 nA. The detected elements in sphalerite are Cu, Fe, S, and Zn calibrated using the following standards: CuFeS 2 (Cu), FeS 2 (Fe, S), and ZnS (Zn). We used previously published fluid data for H 2 S and H 2 of the examined vent sites (Table 1) to calculate f S 2 and f O 2 of emanating fluids (Table DR3) in order to compare these results with the chemical composition of sphalerite. Our calculations are based on fluid temperatures and H 2 (aq) and H 2 S(aq) concentrations, as shown by the following reactions: (1) H 2 S(aq) = H 2 (aq) + 0.5S 2 (g) (2) H 2 (aq) + 0.5 O 2 (g) = H 2 O The equilibrium constants for these reactions were computed using SUPCRT92 (Johnson et al., 1992) for the specific temperatures of the individual vents and a constant pressure of 50MPa.