Conditions of ascent, degassing and extrusion of volatile-rich alkali basalt during the powerful 2002 flank eruption of Mount Etna (Italy)
N. Spilliaert1, P. Allard1,2, N. Métrich1and A.V. Sobolev 3 logo_tutelle logo_tutelle 
In October 2002-January 2003 Mount Etna produced a highly explosive flank eruption, with several unusual features, soon after a shorter analogous event in 2001. We decipher the origin and mechanisms of this second eruption from the chemistry and volatile (H2O, CO2, S, Cl) content of its bulk products and their olivine-hosted melt inclusions, focussing on the south flank main sequence. Our results demonstrate that powerful lava fountains and dense ash columns during the initial phase of the eruption were sustained by closed system ascent of a batch of primitive, volatile-rich (≥4 wt%) basaltic magma that rose from depths ≥10 km b.s.l.. This magma - the most primitive since 140 years – probably represents the alkali-rich parental end-member responsible for Etna lavas’ evolution since the early 1970s. Its deep input likely pressurised the shallow plumbing system several weeks before the eruption, even though its sudden extrusion through already opened fractures may have been facilitated by eastward flank spreading. In fact, most of the eruption was subsequently fed by the extrusion and degassing of larger but slightly more evolved amounts of the same magma that were ponding at 6-4 km b.s.l., in agreement with seismic data and with the lack of pre-eruptive SO2 accumulation above the initial depth of sulphur exsolution (~3 km b.s.l.). While ponding, this magma was flushed and dehydrated by a concentrated CO2-rich gas phase of deeper derivation, a process that may commonly affect the plumbing system of Etna and other alkali basaltic volcanoes elsewhere. 1 Laboratoire Pierre Süe, CNRS-CEA, Saclay, France 2 Istituto Nazionale di Geofisica e Vulcanologia (INGV), Catania, Italy. 3 Max-Planck-Institut f. Chemie, Mainz, Germany Communication: European Geoscience Union General Assembly 2004, session VGP6 Physics and chemistry of volcano degassing Submitted for publication to Journal of Geophysical Research (2005) 

Maj : 03/08/2005 (516)

 

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