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| Titel |
The dynamics of magma chamber refilling at the Campi Flegrei caldera. |
| VerfasserIn |
Chiara Paola Montagna, Melissa Vassalli, Antonella Longo, Paolo Papale, Salvatore Giudice, Gilberto Saccorotti |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039668
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| Zusammenfassung |
| The volcanologic and petrologic reconstructions of several eruptions during the last tens of
thousand years of volcanism at the Campi Flegrei caldera show that in most cases a small,
chemically evolved, partially degassed magma chamber was refilled by magma of
deeper origin shortly before the eruption. New magma input in a shallow chamber is
revealed from a variety of indicators, well described in the literature, that include
major-trace element and isotope heterogeneities, and crystal-liquid disequilibria
(e.g., Arienzo et al., Bull. Volcanol., 2009). In the case of the 4100 BP Agnano
Monte Spina eruption, representing the highest intensity and magnitude event of
the last epoch of activity, it has been suggested that the refilling occurred within a
few tens of hours from the start of the eruption. Notably, in such a case the two
end-member magmas that mixed shortly before eruption onset are not recognized as
individual members in the deposits, rather, their composition and characteristics are
reconstructed from small scale disequilibria, revealing that a relatively short time was
sufficient for efficient mixing of the liquid components. In order to investigate the
dynamics of magma chamber refilling and mixing at Campi Flegrei we have applied the
GALES code (Longo et al., Geophys. Res. Lett., 2006) in a series of numerical
simulations. The initial and boundary conditions have been defined in the frame
of two subsequent projects coordinated by INGV and funded by the Italian Civil
Protection Department, that gather a large number of experts on Campi Flegrei, and are
consistent with the bulk of knowledge on the deep magmatic system. In all cases
an initial compositional interface is placed at a certain depth, with non-degassed,
buoyant magma placed below. The simulations investigate both the dynamics in
a very large, 8 km deep reservoir revealed by seismic tomography (Zollo et al.,
Geophys. Res. Lett., 2008), and those in shallower and smaller chamber systems
connected by dykes and representative of pre-eruptive conditions. The numerical
results reveal the complex dynamics of magma mixing, dominated by the interplay
between buoyant magma rise and dense magma sinking. In all simulated cases
efficient mixing takes place at dyke levels, the buoyant magma entering the chamber is
already a mixture of the two initial end-members, and the initial deep magma is
never found as an individual component in the chamber. Over the time scale of our
longest simulation (about 8 hours of real time), and with reference to the spatial
resolution of our simulations (max 1 m), the magma chamber is occupied by a
nearly homogeneous mixture of the two initial end-members, with minor but still
visible density stratification continuously perturbed by the rise of small buoyant
plumes. Consistent with the observations, an eruption occurring a few tens of hours
after new magma ingression would be characterized by a magmatic composition
intermediate between the two initial end-members, that can therefore be revealed only
from small-scale heterogeneities and possibly from crystal-liquid disequilibria. |
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