Contrasting hydrothermal activity at Sierra Negra and Alcedo volcanoes, Galapagos Archipelago, Ecuador |
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| Authors: | Fraser Goff Gary M McMurtry Dale Counce James A Simac Alfredo R Roldán-Manzo David R Hilton |
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| Institution: | (1) Los Alamos National Laboratory, Los Alamos, NM 87545, USA, US;(2) SOEST University of Hawaii, Honolulu, HI 96822, USA, US;(3) Unocal Corporation, Philippines, 14141 Southwest Freeway, Sugar Land, TX 77478, USA, US;(4) INDE, Guatemala City, Guatemala, GT;(5) Department of Earth Sciences, Vrije Universiteit, HV1081 Amsterdam, The Netherlands, NL |
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| Abstract: | 2 and approximately 85% SO2 of the total sulfur gas. Relative amounts of He, Ar, and N2 show a distinct hot-spot signature ( ). The δ13C–CO2 is approximately −3.6‰ and δ34ST is approximately +3.3‰. The δD/δ18O of fumarole H2O indicates steam separation from local meteoric waters whose estimated minimum mean residence time from 3H analyses is ≤40 years. Fumarolic activity at Alcedo is controlled by a caldera-margin fault containing at least seven hydrothermal
explosion craters, and by an intracaldera rhyolite vent. Two explosion craters which formed in 1993–1994 produce approximately
15 m3/s of steam, yet discharge temperatures are ≤97°C. Water content of the total gas is 95–97 mol.%, noncondensible gas is 92–98 mol.%
CO2, and sulfur gas is dominated by H2S. Relative amounts of He, Ar, and N2 show extensive mixing between hot spot and air or air-saturated meteoric water components but the average . The δ13C–CO2 is approximately −3.5‰ and δ34ST is approximately −0.8‰. The δD/δ18O of fumarole steam indicates separation from a homogeneous reservoir that is enriched 3–5‰ in 18O compared with local meteoric water. 3H indicates that this reservoir water has a maximum mean residence time of approximately 400 years and empirical gas geothermometry
indicates a reservoir temperature of 260–320°C. The intracaldera hydrothermal reservoir in Alcedo is probably capable of producing
up to 150 MW; however, environmental concerns as well as lack of infrastructure and power users will limit the development
of this resource.
Received: 19 April 1999 / Accepted: 23 October 1999 |
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| Keywords: | Galapagos Volcanic gases Gas geochemistry Isotope geochemistry Geothermal systems Sierra Negra Alcedo |
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