Gas discharges from four remote volcanoes in northern Chile (Putana, Olca, Irruputuncu and Alitar): a geochemical survey (original) (raw)

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Franco Tassi

Università di Firenze, Dipartimento di Scienze della Terra, Firenze, Italy; CNR-IGG Istituto di Geoscienze e Georisorse, Firenze

Felipe Aguilera

Universidad de Atacama, Departamento de Geología, Copiapó, Chile; Universidad Católica del Norte, Programa de Doctorado en Ciencias mención Geología, Antofagasta

Orlando Vaselli

Università di Firenze, Dipartimento di Scienze della Terra, Firenze, Italy; CNR-IGG Istituto di Geoscienze e Georisorse, Firenze

Thomas Darrah

University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY, U.S.A; University of Massachusetts Boston, Department of Environmental, Earth, and Ocean Sciences, Boston, MA

Abstract

We analyzed gas samples collected from fumaroles and bubbling pools at Irruputuncu, Putana, Olca and Alitar volcanoes located in the central Andes volcanic zone (northern Chile). The Irruputuncu and Putana fumarolic discharges showed outlet temperatures ranging from 83 ˚C to 240 ˚C and from 82 ˚C to 88 ˚C, respectively. The chemical and isotopic (3He/4He, d13C-CO2, d18O-H2O and dD-H2O) compositions of these discharges were similar to medium-to-high temperature volcanic gases from other active volcanoes in this sector of the Andean volcanic chain (e.g. Lascar volcano). Inorganic and organic gas geothermometers for the H2O-CO2-CO-H2, CO2-CH4 and C2-C3 alkenes-alkanes systems indicated equilibrium temperatures that exceed 500 ˚C at the gas sources. These relatively high temperatures are in agreement with the presence of relevantly high concentrations of magmatic gas emissions, including SO2. Olca and Alitar volcano fluid chemistries indicated lower amounts of magmatic-derived gas species, while both the helium and the water isotopic compositions suggested significant fractions of shallow, crustal/meteoric-originated fluids. These indicate contributions from a hydrothermal environment with temperatures <400 ˚C. The geochemical and isotopic features derived from the present study show that the Irruputuncu, Putana, Olca and Alitar volcanoes should be considered as active and thus warrant periodic geochemical monitoring to determine the evolution of these systems and their potential hazards.

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How to Cite

Tassi, F., Aguilera, F., Vaselli, O., Darrah, T. and Medina, E. (2011) “Gas discharges from four remote volcanoes in northern Chile (Putana, Olca, Irruputuncu and Alitar): a geochemical survey”, Annals of Geophysics, 54(2). doi: 10.4401/ag-5173.

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