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gas vents suddenly and violently opened from the seafloor at the depth of 10-15 m, with an unusually high gas
flux and superimposing on the already existing submarine fumarolic field. Starting from the 12th November
2002 a discontinuous geochemical monitoring program was carried out. The emissions consisted in an emulsion
whose liquid phase derived from condensation of an uprising vapor phase occurring close to the fluid outlets
without significant contamination by seawater. The whole composition of the fluids was basically H2O- and
CO2-dominated, with minor amounts of typical «hydrothermal» components (such as H2S, H2, CO and light hydrocarbons),
atmospheric-related compounds, and characterized by the occurrence of a significant magmatic gas
fraction (mostly represented by SO2, HCl and HF). According to the observed temporal variability of the fluid
compositions, between November and December 2002 the hydrothermal feeding system was controlled by oxidizing
conditions due to the input of magmatic gases. The magmatic degassing phenomena showed a transient
nature, as testified by the almost complete disappearance of the magmatic markers in a couple of months and
by the restoration, since January 2003, of the chemical features of the existing hydrothermal system. The most
striking feature of the evolution of the «Panarea degassing event» was the relatively rapid restoration of the typical
reducing conditions of a stationary hydrothermal system, in which the FeO/Fe1.5O redox pair of the rock
mineral phases has turned to be the dominating redox controlling system.
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