Geochemical model of a magmatic–hydrothermal system at the Lastarria volcano, northern Chile
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Lastarria volcano (25°10′ S, 68°31′ W; 5,697 m above sea level), located in the Central Andes Volcanic Zone (northern Chile), is characterized by four distinct fumarolic fields with outlet temperatures ranging between 80°C and 408°C as measured between May 2006–March 2008 and April–June 2009. Fumarolic gasses contain significant concentrations of high temperature gas compounds (i.e., SO2, HCl, HF, H2, and CO), and isotopic ratios (3He/4He, δ13C–CO2, δ18O–H2O, and δD–H2O) diagnostic of magmatic gas sources. Gas equilibria systematics, in both the H2O-H2-CO2-CO-CH4 and alkane–alkene C3 system, suggest that Lastarria fumarolic gasses emanate from a superheated vapor that is later cooled and condensed at relatively shallow depths. This two-stage process inhibits the formation of a continuous aquifer (e.g., horizontal liquid layer) at relatively shallow depth. Recent developments in the magmatic gas system may have enhanced the transfer and release of heat causing shallow aquifer vaporization. The consequent pressure increase and aquifer vaporization likely triggered the inflation events beginning in 2003 at the Lastarria volcano.
KeywordsLastarria volcano Fumarolic gas Ground deformation Fluid geochemistry Andean volcanics
This research was partially financed by D-21050592 CONICYT grant (Government of Chile) (F. Aguilera), the Laboratories of Fluid and Rock Geochemistry of the Department of Earth Sciences and CNR-IGG of Florence (Resp. F. Tassi and O. Vaselli) and Institut de Recherche pour le Développement (IRD-France) (Resp. S. Moune).
Y. Taran, H. Shinohara, P. Delmelle, R. Cioni and two anonymous referees are warmly thanked for their useful and helpful suggestions during the revision of an early version of the manuscript.
The authors wish to express their gratitude to Jaime Llanos (Inorganic Chemical Laboratory-UCN-Chile) for facilities in the samples preparation, to Sylvain Bonvalot (BGI-France) and Joel Ruch (GFZ-Germany/U. Rome 3-Italy) to invite us to participate in the multidisciplinary studies for Lazufre system, to Jorge Lemp (SERNAGEOMIN) for their help during the first sampling campaign, and Franklin Calle, Javier Pastén and Flavio Marín (UCN-Chile) for their help during the second sampling campaigns. Special thanks to Ejército de Chile for its indispensable help and for facilitated us its “house” during the third and fourth campaigns.
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