Fluid geochemistry of Montserrat Island,West Indies |
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| Authors: | G Chiodini R Cioni A Frullani M Guidi L Marini F Prati B Raco |
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| Institution: | (1) Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, I-06100 Perugia, Italy, IT;(2) Ist. Geocronologia e Geochimica Isotopica, CNR, Via C. Maffi 36, I-56127 Pisa, Italy Fax: +39 50 900270, IT;(3) Geotermica Italiana srl, Lung'Arno Mediceo 16, I-56127, Pisa, Italy, IT;(4) Dipartimento de Scienze della Terra, Università di Genova, Corso Europa 26, I-16132 Genova, Italy, IT;(5) Dipartimento Scienze della Terra, Università di Pisa, Via Santa Maria 53, I-56126 Pisa, Italy, IT |
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| Abstract: | Two geochemical surveys carried out in March 1991 and September 1992 revealed the existence of a hydrothermal system in the
southern portion of Montserrat Island, below Soufrière Hills Volcano. This conclusion is supported by the presence of: (a)
the thermal springs of Plymouth which are fed by deep Na–Cl waters (Cl concentration ∼25 000 mg/kg, temperature ca. 250 °C)
mixed with shallow steam-heated waters; (b) the four fumarolic fields of Galway's Soufrière, Gages Upper Soufrière, Gages
Lower Soufrière, and Tar River Soufrière, where acid to neutral, steam-heated waters are present together with several fumarolic
vents, discharging vapors formed through boiling of hydrothermal aqueous solutions. Involvement of magmatic fluids in the
recharge of the hydrothermal aquifers is suggested by: (a) the high 3He/4He ratios of fumarolic fluids, i.e., 8.2 RA at Galway's Soufrière and 5.9 RA at Gages Lower Soufrière; (b) the δD and δ18O values of Na–Cl thermal springs and steam condensates, indicating the involvement of arc-type magmatic water in the formation
of deep geothermal liquids; and (c) the CH4/CO2 ratios of fumarolic fluids, which are lower than expected for equilibrium with the FeO–FeO1.5 hydrothermal rock buffer, but being shifted towards the SO2–H2S magmatic gas buffer.
Received: 26 March 1996 / Accepted: 19 July 1996 |
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| Keywords: | Montserrat Island Soufrière Hills Volcano Fluid geochemistry Hydrothermal fluids Magmatic fluids |
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