Geochemical survey of active volcanoes and geothermal fields in the Central and Southern Andean Volcanic Zone, Chile

Geochemical survey of active volcanoes and geothermal fields in the Central and Southern Andean Volcanic Zone, Chile


Dr. Felipe Aguilera, Universidad Católica del Norte, Antofagasta, Chile


The Central and Southern Andean Volcanic Zone (CAVZ and SAVZ, respectively), which runs parallel to the Central Andean Cordillera marking the border between Chile and Argentina, consists of several volcanoes that have shown historical and recent activity. The intense volcanism in both areas is associated with the subduction process thrusting the oceanic Nazca Plate beneath the South America Plate. This geodynamical setting produces an anomalous geothermal gradient that at its turn gives rise to a widespread geothermal and thermal activity, not necessarily associated with the volcanic structures. Although over 10 geothermal fields and over 100 thermal springs are present along the both zones, the geochemical features of the fluid discharges from these systems are still almost unknown.


Fluids released from the active volcanoes (e.g., Lascar, Lastarria, Tacora, Olca and Alítar) can be regarded as dominated by contribution from a magmatic-related end-member mixed, at variable degrees, with hydrothermal fluids especially at the periphery of the volcanic edifices. Volcanic gases from summit crater fumaroles are invariably characterized by i) high R/Rair values (>5), ii) relatively high SO2 and N2/Ar ratios (up to >1000), the latter being related to sedimentary material incorporated in the subduction process, and iii) relatively high unsaturated/saturated hydrocarbon ratios. The H2S/SO2 ratios, the concentrations of the organic gas fraction and those of the meteoric-related compounds tend to increase at increasing distance from the volcano summit. The fluid discharges from the geothermal fields are compositionally characterized by dominant CO2 and extremely variable concentrations of H2S, CH4, aromatic hydrocarbons and meteoric compounds (i.e. Ar and O2). The R/Rair values in these systems are relatively low (<3). Fluid contributions from continental-marine limestones and organic matter in both volcanic and geothermal systems significantly affect d13C-CO2 values that are comprised in a wide interval (-15 to -0.4 ‰ V-PDB). Gas geoindicators suggest equilibrium temperatures varying from 200 (Torta de Tocorpuri and Pampa Lirima) to 300 °C (El Tatio, Puchuldiza-Tuya, Surire and Pampa Apacheta). Geothermal systems are characterized by presence of highly-saline Na-Cl waters, related to deep contributions from well-developed medium-to-high enthalpy reservoirs. Sulfate-rich waters are found to be prevalently associated with active volcanic systems, being mainly produced by oxidation of S-bearing gas species, although examples of Ca-SO4 water related to interaction with evaporite sequences are commonly discharging from several non-volcanic areas. Water from geothermal fields and thermal areas is predominantly of a meteoric origin, whereas significant contribution of “andesitic water” seems to be present in active volcanic systems.


Two cases of active volcanoes will be presented in details, corresponding to Lastarria volcano (located in the CAVZ), which has been affected by ground deformation since 1998, whereas the case from SAVZ (Planchón-Peteroa-Azufre volcaoes) will be showed as an example for fluids evolution in an active volcano during unrest periods.

Tuesday, June 13 at 4:00 pm to 5:00 pm

Dow Environmental Sciences and Engineering Building, 610
1400 Townsend Drive, Houghton, MI 49931

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Academics, Lectures/Seminars

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Students, Faculty/Staff, Alumni/Friends, General Public

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College of Engineering, Geological and Mining Engineering and Sciences


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