J'ai profité de l'occasion qui m'était offerte sur l'excellent site du Dr. Eric Klemetti - Eruptions pour poser une question au Dr. Boris Behncke de l'INGV-Catania au sujet du mécanisme éruptif de l'Etna.
Pour que vous profitiez de sa réponse et de ses références, je vous fait un "copier-coller".
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Question and Answer with Dr. Boris Behncke of the Italian National Institute of Geophysics and Volcanology in Catania.
Dr. Boris Behncke.
Questions for Dr. Boris Behncke
(Bernard Duyck) Qu'en est-il de l'évolution du mécanisme éruptif de l'Etna d'un volcanisme de point chaud vers celui de subduction ?"
(What's new over the evolution of Etna from a volcanism of a hot point to a volcanism of subduction?)
BB: This refers to a quite provocative publication (Schiano et al. 2001) of Etna changing from a hot-spot to a subduction type volcano and thus becoming more explosive There hasn't been any further research into this area to my knowledge - but certainly Etna has demonstrated that it has more explosive potential than was believed previously, both in the form of new eruptions - in particular, the very ash-rich 2002-2003 eruption - and in evidence coming from research on Etna's eruptive history. We thus know that explosive volcanism is quite common (Coltelli et al., 1998, 2000, 2005) during the past 100,000 years, which is pretty much the period during which Etna grew into the large mountain it is now (for an updated geological history of Etna, see Branca and Del Carlo, 2004). As it seems, the current consensus on why Etna is there is based on another 2001 publication (Doglioni et al. 2001), which places the volcano in a context of extensional tectonics between two different (oceanic and continental) lithospheric domains in the collision zone between the Eurasian and African plates. To the east, in the Ionian Sea, oceanic lithosphere making up the northern margin of the African plate is subducted beneath the southern margin of the Eurasian plate (the Calabrian Arc), the volcanoes of the Aeolian Islands being the result of the subduction-related melting processes. To the west, on the island of Sicily, the northern African margin is characterized by continental lithosphere colliding with continental Eurasian lithosphere, and the convergence process is slower than in the subduction setting to the east. So it can be said, the convergence occurs at two different speeds, and the two domains are separated by a major system of tectonic structures, which are also seismically active (producing, among others, the major earthquakes of 1693 in southeast Sicily and 1908 in the Messina strait area). Movement at these structures is believed to have an extensional (rifting) component that opens what Doglioni et al. (2001) call a "mantle window", and which is held responsible for significant decompression in the underlying mantle, generating magma - in fact, THE magma that feeds Etna. So to my knowledge that's the currently preferred hypothesis concerning the question why Etna is there, and so Etna would actually be a type of volcano unlike all others, which certainly fits with its extremely complicated and versatile dynamics.
Branca, S., Coltelli, M., Groppelli, G. (2004) Geological evolution of Etna volcano. In: Bonaccorso, A., Calvari, S., Coltelli, M., Del Negro, C., Falsaperla, S. (eds). Mt Etna Volcano Laboratory. AGU Geophysical Monograph Series, 143: 49-63.
Coltelli, M., Del Carlo, P., Vezzoli, L. (1998) Discovery of a Plinian basaltic eruption of Roman age at Etna volcano, Italy. Geology, 26: 1095-1098.
Coltelli, M., Del Carlo, P., Vezzoli, L. (2000) Stratigraphic constraints for explosive activity in the past 100 ka at Etna Volcano, Italy. International Journal of Earth Sciences, 89: 665-677.
Coltelli, M., Del Carlo, P., Pompilio, M., Vezzoli, L. (2005) Explosive eruption of a picrite: the 3930 BP subplinian eruption of Etna volcano (Italy), Geophysical Research Letters, 32, L23307, doi:10.1019/2005GL024271R.
Doglioni C., Innocenti F. & Mariotti S. (2001): Why Mt. Etna? Terra Nova, 13: 25-31.
Schiano, P., Clocchiatti, R., Ottolini, L., Busà, T. (2001) Transition of Mount Etna lavas from a mantle-plume to an island-arc magmatic source. Nature, 412: 900-904.
Merci aux Dr. Behncke et Klemetti pour leurs réponses.