Multiple sulfur isotope composition of the hydrothermal vent precipitates in western Pacific

Abstract

Seafloor hydrothermal vent sites are the most suitable places to investigate the interactions between the ocean and lithosphere because of their fast, active, and visible characteristics in addition to having rich repositories of natural resources such as metallic minerals. Recent development in the analytical technique of multiple sulfur isotopes has led to a growing interest in sulfur tracing in geochemical processes as well as an expanded understanding of sulfur systematics. By process-specific characteristics of the multiple sulfur isotope system, current seafloor hydrothermal vent sulfides from mid-oceanic ridges have shown isotope fractionation following the mixing of basaltic sulfide and seawater sulfate in the multiple sulfur isotope system. We report results for sulfur isotopes (32S, 33S, 34S) of hydrothermal vent precipitates from the Eastern Manus Basin, the North Fiji Basin, the Northeastern Lau basin, and Tonga arc in the southwestern Pacific boundary. We analyzed δ34S and δ33S values using a continuous flow - isotope ratio mass spectrometer. The δ34S values are similar to those from previous studies in western pacific areas while the Δ33S values show wide ranges which may depend on the degree of disequilibrium. Most pyrite samples are higher in Δ33S values than those of coexisting chalcopyrite due to fluid evolution during hydrothermal circulation. Our result also conforms to the trend of seafloor hydrothermal vent sulfides from the mid-oceanic ridge. However, Susu Knolls had anomalously high Δ33S values above 33θ = 0.515, which might indicate different processes of evolution in the multiple sulfur isotope system.