Journal
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
Volume 23, Issue 4, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2021GC010259
Keywords
Niuatahi volcano; S and Pb isotopes; LA-ICP-MS; in situ trace elements; pyrite; chalcopyrite; sphalerite; fluid boiling; magmatic volatiles; black smokers
Categories
Funding
- German Bundesministerium fur Bildung und Forschung (BMBF) [03G0263]
- Deutsche Forschungsgemeinschaft (DFG) [KE2395/21]
- Projekt DEAL
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Submarine caldera volcanoes may have multiple hydrothermal systems, and their mineralogical and chemical composition is influenced by processes such as fluid boiling and magmatic volatile influx.
Submarine caldera volcanoes may host several hydrothermal systems along the caldera wall and related to volcanic cones. Fluid boiling and magmatic volatile influx are common processes in shallow (<2,000 mbsl) subduction zone-related environments causing variations in the mineralogical and chemical composition of seafloor hydrothermal mineralizations that remain poorly constrained. The submarine caldera of Niuatahi volcano, Tonga rear-arc, hosts four active vent sites discharging high temperature fluids (<334 degrees C) with variable salinities (369-583 mM Cl) that are indicative of fluid boiling, recorded by distinct Te/As and Te/Au in pyrite, sphalerite, and chalcopyrite. High sulfidation mineral assemblages (e.g., enargite), stable S isotope data and similar trace element signatures in sulfides and native S condensates suggest a minor and/or infrequent contribution of magmatic SO2 to the hydrothermal systems located proximal to the caldera center causing a volatile element (e.g., Se, Bi, Te) enrichment. The hydrothermal system at the northern caldera wall is decoupled from the magmatic SO2 source, as revealed by radiogenic Pb isotopes. Instead, S isotope and trace element constraints propose a host rock-dominated hydrothermal system, lacking a magmatic volatile influx. The observed hydrothermal fractionation processes (fluid boiling) and the distinct metal (loid) sources (magmatic volatiles vs. host rock) represent a continuum from magmatic volatile- to host rock-dominated hydrothermal systems within the Niuatahi caldera. This leads to seafloor mineralizations with spatially selective trace element enrichments, like Te, Se, and Bi (+/- Au, Ag) in the caldera center compared to Au, Ag, Zn, Cd, and Pb at the northern caldera wall.
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