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Sulfur isotopic compositions of fumarolic and plume gases at Mount Etna (Italy) and inferences on their magmatic source
Author(s)
Language
English
Obiettivo Specifico
1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
5/13 (2012)
Electronic ISSN
1525-2027
Publisher
American Geophysical Union
Pages (printed)
Q05015
Issued date
May 30, 2012
Abstract
Here we report new data on the sulfur isotopic compositions (d34S) of fumarolic and plume gases collected
at Mount Etna volcano during 2008–2009. While low-temperature fumaroles are affected by postmagmatic
processes that modify the pristine isotopic signature, high-temperature and plume gases allow
establishment of a d34S range of 0 1‰ for magmatic SO2. We compared our data with those from S
dissolved in primitive melt inclusions from 2002 lava and in whole rocks that erupted during the past
two thousand years. Such a comparison revealed that d34S is systematically lower for magmatic gases than
for sulfur dissolved in the melt. We modeled how isotopic fractionation due to magma degassing process
may vary d34S value in both the melt and gaseous phases. This modeling required assessment of the fractionation
factor (agas-melt). The most recent measurements on the oxidation state of sulfur in basaltic melt
inclusions indicate that nearly all S is dissolved as sulfate (S6+), which would be possible in oxidized magmatic
systems (DNNO ≥ 1). Under these conditions the exsolved gaseous phase is depleted with respect to
the melt and the proposed model fits both gas and melt data, and constrains the Etnean magmatic d34S to
1.0 1.5‰. It is remarkable that the assessed redox conditions—which are significantly more oxidizing
than previously thought—are able to explain why the dominant sulfur species measured in the Etnean
plume is SO2.
at Mount Etna volcano during 2008–2009. While low-temperature fumaroles are affected by postmagmatic
processes that modify the pristine isotopic signature, high-temperature and plume gases allow
establishment of a d34S range of 0 1‰ for magmatic SO2. We compared our data with those from S
dissolved in primitive melt inclusions from 2002 lava and in whole rocks that erupted during the past
two thousand years. Such a comparison revealed that d34S is systematically lower for magmatic gases than
for sulfur dissolved in the melt. We modeled how isotopic fractionation due to magma degassing process
may vary d34S value in both the melt and gaseous phases. This modeling required assessment of the fractionation
factor (agas-melt). The most recent measurements on the oxidation state of sulfur in basaltic melt
inclusions indicate that nearly all S is dissolved as sulfate (S6+), which would be possible in oxidized magmatic
systems (DNNO ≥ 1). Under these conditions the exsolved gaseous phase is depleted with respect to
the melt and the proposed model fits both gas and melt data, and constrains the Etnean magmatic d34S to
1.0 1.5‰. It is remarkable that the assessed redox conditions—which are significantly more oxidizing
than previously thought—are able to explain why the dominant sulfur species measured in the Etnean
plume is SO2.
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