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| Titel |
Quantitative assessment of magmatic refill and overpressure in crustal reservoirs by monitoring He isotope composition from volcanic gases: the case of Mt Etna (Italy) |
| VerfasserIn |
Antonio Paonita, Antonio Caracausi, Mauro Martelli, Andrea Rizzo |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128205
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| Publikation (Nr.) |
 EGU/EGU2016-8171.pdf |
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| Zusammenfassung |
| There is agreement in recognizing episodes of magma injection into crustal chambers as main
triggers of eruptive activity of volcanoes (Caricchi et al., 2014). These events cause in fact a
buildup of the internal pressure in magma chamber, which in turn controls outpouring magma
amount, possible failure of wall-rocks, dike opening, up to a potential eruption. Assessment
of the time-dependent pressurization while occurring in chamber is therefore challenging aim
of current volcanological research. Recent advancements in estimating the time-dependent
pressurization as long as occurring in chamber come from inverse modeling of
ground deformation data, which does not however calculate internal evolution of the
magma reservoir (Gregg et al., 2013; Cannavò et al., 2015). On the other hand, the
geochemistry of volcanic gases has basically addressed to the pressure(depth) of
gas exsolution so far (Caracausi et al., 2003; Aiuppa et al., 2007; Paonita et al.,
2012).
We developed an pioneering tool that computes the changes of 3He/4He isotope ratio of
volcanic gases with respect to a background, as a function of the time-dependent
outflow of volatiles from a chamber subjected to evolution of internal pressure
through an injection event. Our approach postulates a low-3He/4He gas endmember
coming from resident magmas stored in crust, that mixes with a high-3He/4He gas
endmember from deep parental magmas refilling the deep chamber. We couple a mass
balance between the two gas endmembers to a physical model of the magma chamber.
When a deep input pressurizes the chamber, the latter releases large amounts of the
high-3He/4He gas endmember, so as to change 3He/4He of discharged volcanic
gases.
We applied the model to the long-term series of He isotope ratios from geochemical
monitoring of some peripheral gas emissions at the base of Mt Etna, fed by magmatic
degassing occurring at 200-400 MPa (Paonita et al., 2012). The isotope ratios have in fact
displayed phases of increase occurred at all the sampled emissions some months before
the onset of eruptions, due to deep magma recharges. This behaviour has been
systematic for all the main eruptive phases occurred at Mt Etna since 2001. For most
of the events, we quantitatively estimated the rate of magmatic refill during the
pre-eruptive recharges of the system, as well as the growth of the overpressure in the deep
chamber. Failure of the wall rocks and dike opening is also explained in the case
of 2001 eruption, because chamber overpressure overcame the yield strength of
rocks.
The results suggest that key parameters as the rate of magma inflow and the volume
change in deep chamber can be estimated prior to impending eruptions and directly compared
to inferences from geodetic signals. |
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