Geochemical model of a magmatic–hydrothermal system at the Lastarria volcano, northern Chile

• Published in: Bulletin of volcanology 2012, Vol.74 (1), p.119-134
• Main Authors: Aguilera, Felipe, Tassi, F., Darrah, T., Moune, S., Vaselli, O.
• Format: Article
• Language: English
• Subjects: Aquifers; Carbon dioxide; Crystalline rocks; Deformation; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Sciences; Exact sciences and technology; Fluid dynamics; Geochemistry; Geology; Geophysics/Geodesy; Global Changes; High temperature; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Magma; Mineralogy; Natural hazards: prediction, damages, etc; Research Article; Sciences of the Universe; Sedimentology; Sulfur dioxide; Systematics; Vaporization; Volcanoes; Volcanology
• ISSN: 0258-8900; 1432-0819
• DOI: 10.1007/s00445-011-0489-5

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., SO 2 , HCl, HF, H 2 , and CO), and isotopic ratios ( 3 He/ 4 He, δ 13 C–CO 2 , δ 18 O–H 2 O, and δD–H 2 O) diagnostic of magmatic gas sources. Gas equilibria systematics, in both the H 2 O-H 2 -CO 2 -CO-CH 4 and alkane–alkene C 3 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.