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New insights into the magmatic-hydrothermal system and volatile budget of Lastarria Volcano, Chile; integrated results from the 2014 IAVCEI CCVG 12 (super th) volcanic gas workshop

Taryn Lopez, Felipe Aguilera, Franco Tassi, J. Maarten de Moor, Nicole Bobrowski, Alessandro Aiuppa, Giancarlo Tamburello, Andrea L. Rizzo, Marco Liuzzo, Fatima Viveiros, Carlo Cardellini, Catarina Silva, Tobias Fischer, Philippe Jean-Baptiste, Ryunosuke Kazayaha, Silvana Hidalgo, Kalina Malowany, Gregor Lucic, Emanuela Bagnato, Baldur Bergsson, Kevin Reath, Marcello Liotta, Simon Carn and Giovanni Chiodini
New insights into the magmatic-hydrothermal system and volatile budget of Lastarria Volcano, Chile; integrated results from the 2014 IAVCEI CCVG 12 (super th) volcanic gas workshop
Geosphere (Boulder, CO) (May 2018) 14 (3): 983-1007

Abstract

Recent geophysical evidence for large-scale regional crustal inflation and localized crustal magma intrusion has made Lastarria volcano (northern Chile) the target of numerous geological, geophysical, and geochemical studies. The chemical composition of volcanic gases sampled during discrete campaigns from Lastarria volcano indicated a well-developed hydrothermal system from direct fumarole samples in A.D. 2006, 2008, and 2009, and shallow magma degassing using measurements from in situ plume sampling techniques in 2012. It is unclear if the differences in measured gas compositions and resulting interpretations were due to artifacts of the different sampling methods employed, short-term excursions from baseline due to localized changes in stress, or a systematic change in Lastarria's magmatic-hydrothermal system between 2009 and 2012. Integrated results from a two-day volcanic gas sampling and measurement campaign during the 2014 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Commission on the Chemistry of Volcanic Gases (CCVG) 12 (super th) > Gas Workshop are used here to compare and evaluate current gas sampling and measurement techniques, refine the existing subsurface models for Lastarria volcano, and provide new constraints on its magmatic-hydrothermal system and total degassing budget. While compositional differences among sampling methods are present, distinct compositional changes are observed, which if representative of long-term trends, indicate a change in Lastarria's overall magmatic-hydrothermal system. The composition of volcanic gases measured in 2014 contained high proportions of relatively magma- and water-soluble gases consistent with degassing of shallow magma, and in agreement with the 2012 gas composition. When compared with gas compositions measured in 2006-2009, higher relative H (sub 2) O/CO (sub 2) ratios combined with lower relative CO (sub 2) /St and H (sub 2) O/St and stable HCl/St ratios (where St is total S [SO (sub 2) + H (sub 2) S]) are observed in 2012 and 2014. These compositional changes suggest variations in the magmatic-hydrothermal system between 2009 and 2012, with possible scenarios to explain these trends including: (1) decompression-induced degassing due to magma ascent within the shallow crust; (2) crystallization-induced degassing of a stalled magma body; (3) depletion of the hydrothermal system due to heating, changes in local stress, and/or minimal precipitation; and/or (4) acidification of the hydrothermal system. These scenarios are evaluated and compared against the geophysical observations of continuous shallow inflation at approximately 8 km depth between 1997 and 2016, and near-surface (<1 km) inflation between 2000 and 2008, to further refine the existing subsurface models. Higher relative H (sub 2) O/CO (sub 2) observed in 2012 and 2014 is not consistent with the depletion or acidification of a hydrothermal system, while all other observations are consistent with the four proposed models. Based on these observations, we find that scenarios 1 or 2 are the most likely to explain the geochemical and geophysical observations, and propose that targeted shallow interferometric synthetic-aperture radar (InSAR) studies could help discriminate between these two scenarios. Lastly, we use an average SO (sub 2) flux of 604 + or - 296 t/d measured on 22 November 2014, along with the average gas composition and diffuse soil CO (sub 2) flux measurements, to estimate a total volatile flux from Lastarria volcano in 2014 of approximately 12,400 t/d, which is similar to previous estimates from 2012.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 14
Serial Issue: 3
Title: New insights into the magmatic-hydrothermal system and volatile budget of Lastarria Volcano, Chile; integrated results from the 2014 IAVCEI CCVG 12 (super th) volcanic gas workshop
Affiliation: University of Alaska-Fairbanks, Geophysical Institute, Fairbanks, AK, United States
Pages: 983-1007
Published: 20180507
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 93
Accession Number: 2018-055904
Categories: Quaternary geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables, sketch map
S25°10'00" - S25°10'00", W68°31'00" - W68°31'00"
Secondary Affiliation: Universidad Catolica del Norte, CHL, ChileUniversity of Florence, ITA, ItalyUniversidad Nacional de Costa Rica, CRI, Costa RicaJohannes Gutenberg-Universitaet Mainz, DEU, GermanyUniversita di Palermo, ITA, ItalyIstituto Nazionale di Geofisica e Vulcanologia, Sezione di Bologna, ITA, ItalyIstituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, ITA, ItalyUniversity of the Azores, PRT, PortugalUniversita di Perugia, ITA, ItalyUniversity of New Mexico, USA, United StatesLaboratoire des Sciences du Climat et del'Environnement, FRA, FranceJapanese Geological Survey, JPN, JapanEscuela Politecnica Nacional, ECU, EcuadorMcGill University, CAN, CanadaIcelandic Meteorological Office, ISL, IcelandCornell University, USA, United StatesMichigan Technological University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201830
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