Search

Hydrothermal systems located at intra-oceanic volcanic arcs and in back-arc basins reveal a complex sulfur cycling. Here we present multiple sulfur isotope data for dissolved sulfide and sulfate in hydrothermal fluids from vent sites at the southern Kermadec and the northern Tonga island arcs and the NE Lau Basin. δ34S values for H 2 S range from −7.4 to +4.6‰ for hydrothermal fluids from arc volcanoes and from +0.2 to +4.5‰ for those located in the NE Lau Basin. Ranges for Δ33S values are −0.010 to +0.033‰ and −0.016 to +0.011‰, respectively. SO 4 2− in fluids from hydrothermal vents at Macauley caldera, the Brothers volcanic cones, and Niua North show ranges in δ34S and Δ33S from +16.7 to +24.7‰ and +0.013 to +0.049‰. The multiple sulfur isotope data suggest a contribution to the hydrothermal sulfur budget from the disproportionation of magmatic SO 2 for most hydrothermal vent sites from the Kermadec arc, whereas H 2 S at the NE Lau Basin vent sites is thought to result mainly from two-component mixing between host rock-derived sulfur and seawater sulfate with an additional local contribution from SO 2 disproportionation. Data from Brothers NW Caldera suggest isotope exchange between H 2 S and SO 4 2−, whereas lowering of fluid acidity by dissolution of mineral phases occurs at the Brothers Lower Cone. δ34S values between −8.5 and +3.1‰ and Δ33S values between +0.009 and +0.036‰ for elemental sulfur indicate changing redox conditions and/or a decrease of magmatic SO 2 in the hydrothermal fluids at Macauley, Haungaroa, Brothers Lower Cone, Niua North and Niuatahi. We conclude that acid sulfate venting in particular shows the highest variability in sulfur isotopic composition of hydrothermal sulfur, irrespective of whether located at an intra-oceanic arc or in a back-arc basin. Sulfur isotope heterogeneity is due to variable contributions from SO 2 disproportionation and host rock compositions. [ABSTRACT FROM AUTHOR]