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Experimental simulation of pre-eruptive conditions of
“yellow pumice”-Stromboli (Aeolian arc)-Italy

Abstract : In the most recent years big attention was been addressed to the volcanic hazard. Stromboli is
characterized by a persistent activity. Hazards associated with volcanic activity at Stromboli may
include gas emissions and fall-outs of volcanic ash and bombs, but more global hazards can not be
dismissed such as large-scale eruptions or tsunamis generated in the Tyrrhenian sea as a result of flank
collapse of the volcano. Stromboli is actively monitored by italian groups and institutions. The present
project complements these efforts in providing an experimentally-based modelling of how magma
ascends beneath Stromboli. Knowledge of the physicochemical properties of magmas may improve in
the long-term the interpretation of geophysical signals and the understanding of the real-time
behaviour of the volcano.
Its normal activity is periodically interrupted by emission of lava flow or much more energetic
explosions. The most energetic explosions are distinguished in major explosions (1-2 per year) and
paroxysms (one event in 5 to 15 years).
Most of the existing works and dynamic models of the Stromboli's activity are done on the normal
activity, but, maybe, studying the paroxysm can be the important means to understand its persistent
The paroxysm permits to study mingling, crystallisation and degassing processes in the volcanic
system. During major explosion and paroxysm, a particular product constituted by a yellow pumice
intermingled with a black scoria is emitted. The yellow pumice is a crystal-poor (< 10 vol % of
crystals), gold-coloured, highly vesiculated pumice and represent the most primitive magma ever
erupted at Stromboli; the black scoria is crystal-rich (~50 vol % of crystals), rather dense, lower
vesiculated, usual product of the normal activity. The two portions are so different in features, but so
similar in bulk chemical composition ranging from K-rich basalt and shoshonitic basalt. They display
only slight variations in major and trace elements contents, and rare earth element patterns. The very
big differences are played by the volatile content (H2O-CO2-S) on the two part of rock.
The aims of this petrological experimentally study are: (i) to characterize the source region of
magmatism, (ii) to constrain the P-T-aH2O during the ascent path of yellow pumice magma, (iii) to
constrain the derivation of the black scoria from the yellow pumice magma during the rapid ascent
path in the shallow level of the Stromboli conduit.
The volatiles constituents play a narrower importance in the phase relations as in the chemical and
physical properties of the magmas. We planned two series of experiments, an isobaric 4 kbar (1175-
1050°C) section and an isothermal 1100°C (4-0.5 kbar) section, in variable water content, from
undersaturation near to the water saturation. We chosen as starting material one of the most primitive
yellow pumice never erupted. The starting composition will be prepared as glass, to avoid any residual
crystal, and glass finely crushed. Some additional experiment was carried out in order to ascertain the primitivity of our starting composition. Few experiments were done in mixed fluid volatiles (H2O +/-
CO2 +/- S).
According our experimental data yellow pumice is a near primitive magma in equilibrium with
clinopyroxenite source at P-T of stagnation: the first phase to appears on the liquidus is pyroxene;
olivine follows at lower temperature, for lower hydration conditions. Clinopyroxene plays an
important role at higher pressure conditions (4 kb), plagioclase instead is the most relevant phase at
lower pressure. It was possible to derive an experimental geobarometer from the cotectic ol/cpx ratio:
if we apply this correlation between pressure and cpx(ol ratio, we can obtain a pressure of
crystallisation for yellow pumice (3.7-2.9 kb) and black scoria (1.2-0.6 kb). Our experimental data,
show a clear correlation between Ca content in clinopyroxene and water content in the melt and this
correlation can be used a geohygrometer in the 3-phase assemblage, to infer the water content in
natural samples. The last important results are about empirical solubility data of both together H2OCO2
that are in bad accordance with most used thermodynamic models that overestimate the pressure
of saturation of nearly 50%
keyword : Stromboli
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Submitted on : Wednesday, October 25, 2006 - 5:15:58 PM
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  • HAL Id : tel-00109864, version 1



Ida Di Carlo. Experimental simulation of pre-eruptive conditions of
“yellow pumice”-Stromboli (Aeolian arc)-Italy. Applied geology. Università degli studi di Palermo, 2005. English. ⟨tel-00109864⟩



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