Origin of components in Chilean thermal waters |
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| Authors: | François Risacher Bertrand Fritz Arturo Hauser |
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| Affiliation: | 1. Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 803 Plaza Ercilla, 8370450 Santiago, Chile;2. Centro de Excelencia en Geotermia de los Andes (CEGA), Universidad de Chile, 803 Plaza Ercilla, 8370450 Santiago, Chile;3. School of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8, 1RJ, UK;4. Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;1. Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Chile/Centro de Excelencia en Geotermia de los Andes (CEGA), Chile;2. Advanced Mining Technology Center, Universidad de Chile, Chile;1. Observatorio Volcanológico de los Andes del Sur, Servicio Nacional de Geología y Minería, Rudecindo Ortega 03850, Temuco, Chile;2. Programa de Doctorado en Ciencias Geológicas, Universidad de Concepción, Víctor Lamas 1290, Concepción, Chile;3. Departamento de Ciencias de la Tierra, Facultad de Ciencias Químicas, Universidad de Concepción, Víctor Lamas 1290, Concepción, Chile;4. Servicio Nacional de Geología y Minería, Av. Santa María 0104, Santiago, Chile;5. Research Center for Integrated Risk Management (CIGIDEN), Av. Vicuña Mackenna 4860, Santiago, Chile;6. Departamento de Geología y Obras Civiles, Facultad de Ingeniería, Universidad Católica de Temuco, Chile;7. Departamento de Ciencias Físicas, Facultad de Ingeniería, Universidad de la Frontera, Casilla 54-D, Temuco, Chile;1. Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, China;2. Key Laboratory of Salt Lake Geology and Environment of Qinghai Province, Xining 810008, China;3. Department of Geological Sciences and Environmental Studies, Binghamton University, Binghamton, NY 13902, USA;4. University of Chinese Academy University, Beijing 100085, China;1. Servicio Nacional de Geología y Minería, Red Nacional de Vigilancia Volcánica, Santiago, Chile;2. Departamento de Geología, Universidad de Chile, Santiago, Chile/ Centro de Excelencia en Geotermia de los Andes (CEGA)/ Advanced Mining Technology Center (AMTC) |
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| Abstract: | Thermal waters of northern (18°–27°S) and southern (37°–45°S) Chile occur in two very different climatic, geologic and hydrologic environments: arid closed basins with abundant evaporites in the north; humid climate and well drained valleys in the south. The origin and behavior of the main components of the two groups of waters are examined and compared to each other. The modeling of the alteration of volcanic rocks leads to water compositions very different from those observed both in the north and south. In addition to hydrothermal alteration and deep emanations, the Cl/Br ratio reveals a major contribution of saline waters to the two groups: infiltrating brines from salt lakes in the north; seawater in the south.In the north, concentrations of Cl, Br, Na, K, Ca, SO4, Li, B, Si result from the mixing of alteration waters with recycled brines. Hydrothermal alteration is obscured by this massive saline input, except for Mg. δ34S values are consistent with an origin of sulfate from salar brines, which are themselves derived from deep Tertiary gypsum. In the south, two processes account for the composition of thermal waters: mixing of alteration waters with seawater and deep magmatic contribution. The mixing process controls the concentration of Cl, Br, Na, Alk, Si, K, Ca, Mg. Magmatic inputs are detectable for SO4, Li and B. δ34S suggests that sulfate stems from the mixing of alteration waters with either marine SO4 in coastal waters or with deep SO2 in inland waters. In both the north and south, the Mg concentration is drastically lowered (<1 μmol/L) by the probable formation of a chlorite-type mineral. In the south, very small amounts of seawater (<1% in volume) are sufficient to imprint a clear signature on thermal waters. Not only coastal springs are affected by seawater mixing, but also remote inland springs, as far as 150 km from the sea. Subduction of marine sediments in the accretive margin could be the source of the marine imprint in thermal waters of southern Chile. Seawater may be expelled from the subducted lithosphere and incorporated into the mantle source. |
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