The helium isotopic ratio of crater, beach and submarine fumaroles, water wells, and soil gases at Vulcano Island has been, since 1987, repeatedly measured. The 3He/4He from crater fumaroles (F5 and FA) oscillates biennially between 4.9 and 6.0-6.2 R/Ra. The periodicity of the 3He/4He oscillation may be linked to pressure variations in a deep gas reservoir. Chemical and carbon isotope variations during the same period closely reflect trends shown by helium. These simultaneous variations, chemical and isotopic, suggest a close relationship between these species and reflect one dominant process, which belong to the routine activity of the volcano. The 40Ar/36Ar ratio up to 1200 is not consistent with the presence of an air-rich source and suggests the addition of radiogenic argon. Neon data (20Ne/22Ne and 21Ne/22Ne) indicates that a crustal component is present beneath the volcano. Heavy carbon, 0‰ ∼ -2‰, also supports the existence of a crustal component. The isotopic data here obtained do not indicate that the recorded variations (chemical and isotopic) indicate a "period of unrest" at Vulcano Island. The present phase of activity is explained with a two-state model of the feeding sources of the volcano: (a) a gas release from intermediate and surficial sources and (b) a magmatic pulse, 3He-rich, from a deep gas reservoir (not migration of magma) which continuously mixes with more surficial fluids. Additions of surficial (air saturated waters) or atmospheric fluids are minor and may occur during the ascent of the gas phase to the surface or, more likely, be added at the time of the gas collection. Copyright 1999 by the American Geophysical Union.

Intensive gas sampling of noble gases and carbon at Vulcano Island (southern Italy)

TEDESCO, Dario;
1999

Abstract

The helium isotopic ratio of crater, beach and submarine fumaroles, water wells, and soil gases at Vulcano Island has been, since 1987, repeatedly measured. The 3He/4He from crater fumaroles (F5 and FA) oscillates biennially between 4.9 and 6.0-6.2 R/Ra. The periodicity of the 3He/4He oscillation may be linked to pressure variations in a deep gas reservoir. Chemical and carbon isotope variations during the same period closely reflect trends shown by helium. These simultaneous variations, chemical and isotopic, suggest a close relationship between these species and reflect one dominant process, which belong to the routine activity of the volcano. The 40Ar/36Ar ratio up to 1200 is not consistent with the presence of an air-rich source and suggests the addition of radiogenic argon. Neon data (20Ne/22Ne and 21Ne/22Ne) indicates that a crustal component is present beneath the volcano. Heavy carbon, 0‰ ∼ -2‰, also supports the existence of a crustal component. The isotopic data here obtained do not indicate that the recorded variations (chemical and isotopic) indicate a "period of unrest" at Vulcano Island. The present phase of activity is explained with a two-state model of the feeding sources of the volcano: (a) a gas release from intermediate and surficial sources and (b) a magmatic pulse, 3He-rich, from a deep gas reservoir (not migration of magma) which continuously mixes with more surficial fluids. Additions of surficial (air saturated waters) or atmospheric fluids are minor and may occur during the ascent of the gas phase to the surface or, more likely, be added at the time of the gas collection. Copyright 1999 by the American Geophysical Union.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11591/199637
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