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| Titel |
The geochemistry of gas emissions as a tool to unravel the magma dynamics at Mt Etna (Italy) |
| VerfasserIn |
Antonio Caracausi, Mauro Martelli, Antonio Paonita, Andrea Luca Rizzo |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092745
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| Publikation (Nr.) |
 EGU/EGU2014-7104.pdf |
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| Zusammenfassung |
| Since 1996 we have been performing a discrete geochemical monitoring of five
peripheral gas emissions located at the base of Mt Etna, with a frequency of roughly 2
samplings campaigns per month. This has been integrated since 2007 with the periodic
sampling of few fumaroles located at the top of Etna. Chemical composition of gases
displayed that shallow processes such as interaction with aquifers modify the pristine
gas mixture. Such effects were quantitatively modeled and removed. The obtained
systematics of He-Ar-CO2 lead us to assess the absolute pressure at which the gas
are released from the magma. Peripheral gases reflect the degassing of magma
bodies residing at depths of 200-400 MPa, while crater fumaroles are fed by magmas
residing at shallower levels (i.e., up to ~130 MPa). These estimations are in good
agreement with the depth of the two main magma ponding zones (i.e., 5-12 km and
2-3 km b.s.l.) inferred by petrological and geophysical studies. Besides the pure
magma degassing process, gases also reflect a mixing of volatiles exsolved from
batches of melts located at variable pressures. The long-term monitoring of gases
from the base and the top of the volcano displayed increasing phases of 3He/4He
occurring some months before an eruptive activity. Such increases are interpreted as the
intrusion of primitive batches of 3He-rich magma into the deepest portion of the
plumbing system. This behaviour has also been observed before 2011-2012 and 2013,
when a terminal eruptive activity has episodically occurred and is still ongoing
(January 2014). This phase is characterized by frequent fire fountains coupled to
small lava flows. Finally, we underline that the maximum 3He/4He value of free gas
emissions (~7.6 Ra, where Ra = atmospheric 3He/4He) is in perfect agreement with the
maximum value we measured in the fluid inclusions of mafic phenocrysts of Etna. |
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