The 2011–2012 paroxysmal eruptions at Mt. Etna volcano: Insights on the vertically zoned plumbing system

The activity ofMt. Etna volcano from January 2011 to April 2012 was characterized by 24 paroxysmal, short-duration
(from a few to several hours) eruptions at the New South-East summit crater. Despite the violence of the
activity, no appreciable geophysical signals were recorded during this period, except for an increase in seismic
tremors just minutes/hours before the occurrence of the paroxysm. This type of activity represents a significant
shift from the mainly effusive eruptions of 2004, 2006, and 2008/2009, as well as from the lateral rift-related
events of 2001 and 2002/2003.
The 2011–2012 paroxysmal activity thus represents an important opportunity to better understand the effects of
different magmatic parameters (i.e., P-T-fO2) and magmatic H2O content on the crystallization and fractionation
processes. To this aim the petrographic and geochemical features of lava and scoria clasts from 10 paroxysmal
events have been investigated. Fractional crystallization modelling indicates that most of the eruptions are related
to magmas rising along the vertically-developed feeding systemof the volcano, accompanied by one main recharge
of a more primitive, deep-seated magma feeding the 4/3/2012 event. Olivine-, clinopyroxene-, and
plagioclase-melt equilibria and thermobarometric calculations were performed in order to estimate the crystallization
conditions of magmas. These calculations reveal that the erupted products contain different phenocryst
populations in equilibrium with a spectrum of primitive to more evolved magma compositions. On the basis of
crystal composition, crystal-melt equilibriumconditions and thermobarometric estimations, four main magmatic
facies have been recognized: F1, 1600 MPa at 1270 °C (Ol Fo88); F2, 800 MPa to 600MPa at 1178 °C to 1151 °C
(Ol Fo84–78); F3, 450 MPa to 250 MPa at 1139 °C to 1118 °C (Ol Fo79–74); F4, b250 MPa at b1120 °C (Ol Fo75–70).
The overall geochemistry and thermobarometric data allowus to characterize the central feeding systemas continuous
and vertically zoned. During the 2011–2012 activity the studied 30/7/11, 29/8/11, 8/9/11, 18/3/11 and
24/4/12 events were fed by magma residing at F3 and F4 facies. Mafic magma influx from deeper F2 facies occurred
18/2/11 and 20/8/11,with a major recharge event before the 4/3/12 eruption. The primitive magma is testified
by rare olivine crystals equilibrated at the F1 facies, located at crust-mantle boundary depth and close to
liquidus temperature.