Causes for variable hydrothermal vent fluid compositions in intraoceanic arcs : insights from fluid compositions and mineral precipitates of the South Kermadec Arc

This work presents investigations of high-T hydrothermal vent fluids, associated mineral precipitates and volcanic rocks from three submarine volcanos in the South Kermadec intraoceanic arc (Brothers Caldera, Haungaroa Volcano, Macauley Caldera). Mineralogical investigations, vent fluid compositions and fluid inclusion studies are discussed. Reaction path models simulate the influence of host rock compositions and the integrated fluid flux on the formation of massive sulfides. Further models demonstrate how addition of magmatic SO2 to hydrothermal systems generates arc typical magmatic-hydrothermal fluids and influences their REE composition. Vent fluid compositions, as well as salinities and formation temperatures in mineral precipitates from seawater-dominated hydrothermal fluids, point to boiling processes of rising solutions. The investigations demonstrate how magma degassing and boiling are key processes responsible for the chemical diversity of arc hydrothermal fluids.