Sulfur and lead isotopes composition of hydrothermal chimney in the NE Lau Basin: Possible link between the contribution of magmatic volatiles to the hydrothermal system and the extent of subduction i

Abstract

Hydrothermal vent fluids and deposits found at convergent margin (mainly back-arc basin spreading centers and submarine arc volcanoes) usually show diverse chemistry when compared with those at mid-ocean ridges. The diversity of hydrothermal vents in the convergent margin can be attributed to several factors, including composition of substrate rock, the depth and structure of the substrate, and the contribution of magmatic volatiles to the hydrothermal system. In particular, the contribution of magmatic volatile to the hydrothermal system, characterized by its anomalously low sulfur isotope ratios of sulfides, is reported for several submarine hydrothermal systems at convergent margin but not at mid-ocean ridges. We present here sulfur and lead isotope composition of hydrothermal precipitates and trace elements composition of substrate rocks collected from three active hydrothermal venting sites in the NE Lau Basin: the Fonualei Rift and Spreading Center (FRSC), Northeast Lau Spreading Center (NELSC), and an off-axis caldera (MTJ-1). Sulfur isotope composition of various sulfur compounds (e.g. sulfide, sulfate, and native sulfur) indicates different extent of magmatic contribution for each hydrothermal site in the NE Lau Basin. In addition, chimney sulfides with low sulfur isotope ratios also show more radiogenic lead isotope composition that may reflect mixing of sedimentary lead during subduction. Comparisons of our data with other geochemical data sets published for other hydrothermal vents of the Lau Basin together with other back-arc basins suggest that the differences in contribution of magmatic volatile on hydrothermal system is possibly linked to the extent of subduction input in arc and back-arc basin settings.