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Geochemical evidence for mixing of magmatic fluids with seawater,Nisyros hydrothermal system,Greece
Authors:Email author" target="_blank">Tatjana?BrombachEmail author  Stefano?Caliro  Giovanni?Chiodini  Jens?Fiebig  Johannes?C?Hunziker  Brunella?Raco
Institution:(1) Osservatorio Vesuviano, Via Diocleziano 328, 80124 Napoli, Italy;(2) Institut de Minéralogie et Pétrographie, Université de Lausanne, BFSH2, Lausanne, Switzerland;(3) Istituto di Geocronologia e Geochimica Isotopica, Area della Ricerca CNR, Via Alfieri 1, Ghezzano, Pisa, Italy
Abstract:The chemical and isotopic compositions (δDH2O, δ18OH2O, δ18OCO2, δ13CCO2, δ34S, and He/N2 and He/Ar ratios) of fumarolic gases from Nisyros, Greece, indicate that both arc-type magmatic water and local seawater feed the hydrothermal system. Isotopic composition of the deep fluid is estimated to be +4.9±0.5‰ for δ18O and ?11±5‰ for δD corresponding to a magmatic water fraction of 0.7. Interpretation of the stable water isotopes was based on liquid–vapor separation conditions obtained through gas geothermometry. The H2–Ar, H2–N2, and H2–H2O geothermometers suggest reservoir temperatures of 345±15 °C, in agreement with temperatures measured in deep geothermal wells, whereas a vapor/liquid separation temperature of 260±30 °C is indicated by gas equilibria in the H2O–H2–CO2–CO–CH4 system. The largest magmatic inputs seem to occur below the Stephanos–Polybotes Micros crater, whereas the marginal fumarolic areas of Phlegeton–Polybotes Megalos craters receive a smaller contribution of magmatic gases.
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