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Isotopically (δ13C and δ18O) heavy volcanic plumes from Central Andean volcanoes: a field study
Author(s)
Language
English
Obiettivo Specifico
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/79 (2017)
Pages (printed)
65
Issued date
July 31, 2017
Abstract
Stable isotopes of carbon and oxygen in volcanic
gases are key tracers of volatile transfer between Earth’s interior
and atmosphere. Although important, these data are available
for few volcanoes because they have traditionally been difficult
to obtain and are usually measured on gas samples collected
from fumaroles. We present new field measurements of bulk
plume composition and stable isotopes (δ13CCO2 and δ18OH2O+
CO2) carried out at three northern Chilean volcanoes using
MultiGAS and isotope ratio infrared spectroscopy. Carbon
and oxygen in magmatic gas plumes of Lastarria and Isluga
volcanoes have δ13C in CO2 of +0.76‰ to +0.77‰ (VPDB),
similar to slab carbonate; and δ18O in the H2O + CO2 system
ranging from +12.2‰ to +20.7‰ (VSMOW), suggesting significant
contributions from altered slab pore water and carbonate.
The hydrothermal plume at Tacora has lower δ13CCO2 of
−3.2‰ and δ18OH2O+CO2 of +7.0‰, reflecting various scrubbing,
kinetic fractionation, and contamination processes. We
show the isotopic characterization of volcanic gases in the field
to be a practical complement to traditional sampling methods,
with the potential to remove sampling bias that is a risk when
only a few samples from accessible fumaroles are used to characterize
a given volcano’s volatile output. Our results indicate
that there is a previously unrecognized, relatively heavy isotopic
signature to bulk volcanic gas plumes in the Central Andes,
which can be attributed to a strong influence from components
of the subducting slab, but may also reflect some local crustal
contamination. The techniques we describe open new avenues
for quantifying the roles that subduction zones and arc volcanoes
play in the global carbon cycle.
gases are key tracers of volatile transfer between Earth’s interior
and atmosphere. Although important, these data are available
for few volcanoes because they have traditionally been difficult
to obtain and are usually measured on gas samples collected
from fumaroles. We present new field measurements of bulk
plume composition and stable isotopes (δ13CCO2 and δ18OH2O+
CO2) carried out at three northern Chilean volcanoes using
MultiGAS and isotope ratio infrared spectroscopy. Carbon
and oxygen in magmatic gas plumes of Lastarria and Isluga
volcanoes have δ13C in CO2 of +0.76‰ to +0.77‰ (VPDB),
similar to slab carbonate; and δ18O in the H2O + CO2 system
ranging from +12.2‰ to +20.7‰ (VSMOW), suggesting significant
contributions from altered slab pore water and carbonate.
The hydrothermal plume at Tacora has lower δ13CCO2 of
−3.2‰ and δ18OH2O+CO2 of +7.0‰, reflecting various scrubbing,
kinetic fractionation, and contamination processes. We
show the isotopic characterization of volcanic gases in the field
to be a practical complement to traditional sampling methods,
with the potential to remove sampling bias that is a risk when
only a few samples from accessible fumaroles are used to characterize
a given volcano’s volatile output. Our results indicate
that there is a previously unrecognized, relatively heavy isotopic
signature to bulk volcanic gas plumes in the Central Andes,
which can be attributed to a strong influence from components
of the subducting slab, but may also reflect some local crustal
contamination. The techniques we describe open new avenues
for quantifying the roles that subduction zones and arc volcanoes
play in the global carbon cycle.
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article
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