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11.
Carmelo Ferlito Marco Viccaro Eugenio Nicotra Renato Cristofolini 《Bulletin of Volcanology》2010,72(10):1179-1190
Over the last 2 years, the south east crater (SEC) at Mt. Etna (Italy) has been characterised by the intermittent emission
of lava flows, often accompanied by paroxysmal episodes with violent strombolian activity and/or lava fountains. One of the
most intense and intriguing episodes occurred on November 16, 2006 during strombolian and effusive activity from the very
top of the SEC. At the eastern base of the crater, a violent and short-lasting outburst generated a 300-m-high eruptive curtain
of finely fragmented magma and steam, which collapsed in a few seconds giving rise to a small but significant pyroclastic
flow. The paroxysm was preceded by progressive sliding of the eastern flank of the SEC edifice, which led to the formation
of a large niche. Previously published models explain the outburst as due to rapid vaporisation of water contained in sediments
on contact with hot lava flowing along the flank of the SEC or, alternatively, to gravitational collapse of a destabilised
portion of the eastern flank of the crater. However, several lines of evidence suggest that these models do not adequately
explain the paroxysm, which we propose was associated with the explosive emission of magma during the rapid opening of an
ESE-WNW-oriented fracture at the eastern base of the SEC. Moreover, geochemical data of the products associated with this
episode show that they are the most primitive and gas-rich among those erupted during the entire 2006 period. We suggest that
the paroxysm of November 16, 2006, which occurred at base of the SEC, was a magma outburst due to rapid ground fracturing
related to a drop in confining pressure upon the underlying dyke consequent to the sliding of the eastern flank of the SEC
cone. Specifically, the unloaded shallow portion of the feeding dyke did not restrain the arrival of a new batch of gas-rich
magma, which worked its way out by fracturing the base of the niche at its weakest point. This paroxysm appears significant
because it reveals the potential development of syn-eruptive dynamics acting directly on the uppermost portion of the plumbing
system which is able to generate pyroclastic flows even on basaltic volcanoes such as Mount Etna. 相似文献
12.
Natural Resources Research - 相似文献
13.
Simona Mazziotti Tagliani Eugenio Nicotra Marco Viccaro Antonio Gianfagna 《Mineralogy and Petrology》2012,106(1-2):89-105
The exceptional occurrence of fluorine-rich mineral phases in the benmoreitic lava dome of Mt. Calvario (south-western flank of Mt. Etna) has given the opportunity to understand the genetic process allowing their crystallization. Both primary and secondary mineral associations were found, namely: plagioclase, clinopyroxene, olivine, fluorapatite and iron oxides as primary assemblage, whereas fluoro-edenite and fluorophlogopite, ferroan-enstatite, hematite, pseudobrookite and tridymite as secondary mineralization. In addition to some major and trace elements (e.g., Fe, Ti, Na, K, P, Ba, Rb, Sm, Zr), particularly fluorine and chlorine concentrations of the whole rock are significantly higher than other Etnean prehistoric benmoreites, and cannot be accounted for common differentiation processes in the feeding system. The selective enrichment in some elements has been here attributed to volatile flushing occurring in the plumbing system, with fluid/melt ratio of ~0.65:1. The resulting high amount of fluorine, coupled with its high solubility even at low pressure for benmoreitic melts, finally led to nucleation and growth of F-rich mineral phases during syn- and post-eruptive conditions. 相似文献
14.
P. P. Giacomoni C. Ferlito G. Alesci M. Coltorti C. Monaco M. Viccaro R. Cristofolini 《Bulletin of Volcanology》2012,74(10):2415-2433
Mount Etna volcano is often characterized by bilateral eruptive events, involving both the south (S) and the north east (NE) rifts. The last event occurred in 2002?C2003 from October 27 to January 28. A detailed, stratigraphically time-controlled sampling of lavas and tephra of the southern eruptive fissure was performed in order to (1) track the petrological features of products during the eruption and (2) integrate the results with those previously obtained on the NE rift. Whole-rock composition and textural observations were implemented by major and minor element analyses of plagioclases in lavas and tephra from both sides of the volcano. Fractionation models constrained by mass balance (major and trace elements) and Rayleigh calculations suggest that magmas are linked by the same liquid line of descent by fractionating 9.11?% of a mineral assemblage of Cpx (52.69?%), Plg (21.41), and Ol (7.46?%). These new data allowed us to identify at least two feeding episodes through the southern fissure and infer that high-K2O porphyritic magmas, emitted on both the S and NE rifts, derives by fractionation from the same parent magma. However, lavas and tephra from the southern flank were slightly more primitive. Textural and petrological study of plagioclase moreover indicates that chemical?Cphysical conditions in the deep feeding system were similar for magmas erupting from both rifts as suggested by the presence of dissolved rounded cores in both lavas. Magmas evolved differently on the S and the NE rifts only at shallow levels. Comparison with published seismotectonic data supports the idea that the main magma feeding the eruption on October 27 ascended along the same pathway at depth and was intercepted by the fracture system of the S and NE rifts at shallow depth, between 6 and 3?km b.s.l. 相似文献
15.
At Mt. Etna volcano, the emission of plagioclase megacryst-bearing lavas, known locally as “cicirara”, has occurred rarely
and generally in association with unusual volcanological phenomena. In this work, we interpret the magma chamber processes
and the structural features of the plumbing system that led to the production of these peculiar volcanic rocks, based on a
detailed study of plagioclase megacrysts, including their oscillatory zoning, sieve textures, and fluid inclusions. Patchy
zoning suggests limited ascent in the deep levels of the plumbing system, based on the plagioclase nucleation threshold and
the volatile saturation depth. At intermediate, water-undersaturated levels of the plumbing system ascent is faster, as indicated
by crystals with coarse sieve textures. Storage at shallow, water-saturated levels (less than 6 km deep) is associated with
oscillatory zoning with very small changes in An. Slightly larger An variations coupled with different wavelengths provide
evidence of convection of crystals across distinct zones of the chamber. Stripes of melt inclusions formed at steps of magma
ascent and volatile loss, whereas layers of fluid inclusions may be related to episodes of volatile flushing into the magma
chamber. In contrast, strongly sieve-textured envelopes with An increase and constant FeO may be related to mixing with more
volatile-rich magmas of similar composition. We interpret the repeated occurrence of “cicirara” lavas as evidence that the
shallow portion of the plumbing system underwent a progressive coalescence of a complex network of dykes and sills in response
to increasing rates of magma supply from depth. Major magma withdrawals from this larger reservoir may be linked to episodes
of summit instability associated with major caldera collapses. 相似文献
16.
Mount Etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries.
For about 3 weeks, several eruptive fractures developed, emitting lava flows and tephra that significantly modified the landscape
of the southern flank of the volcano. This event stimulated the attention of the scientific community especially for the simultaneous
emission of petrologically distinct magmas, recognized as coming from different segments of the plumbing system. A stratigraphically
controlled sampling of tephra layers was performed at the most active vents of the eruption, in particular at the 2,100 m
(CAL) and at the 2,550 m (LAG) scoria cones. Detailed scanning electron microscope and energy dispersive x-ray spectrometer
(SEM-EDS) analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous
increase in Ti, Fe, P, and particularly of K and Cl in the upper layers of the LAG sequence. Mass balance and thermodynamic
calculations have shown that this enrichment cannot be accounted for by “classical” differentiation processes, such as crystal
fractionation and magma mixing. The analysis of petrological features of the magmas involved in the event, integrated with
the volcanological evolution, has evidenced the role played by volatiles in controlling the magmatic evolution within the
crustal portion of the plumbing system. Volatiles, constituted of H2O, CO2, and Cl-complexes, originated from a deeply seated magma body (DBM). Their upward migration occurred through a fracture network
possibly developed by the seismic swarms during the period preceding the event. In the upper portion of the plumbing system,
a shallower residing magma body (ABT) had chemical and physical conditions to receive migrating volatiles, which hence dissolved
the mobilized elements producing the observed selective enrichment. This volatile-induced differentiation involved exclusively
the lowest erupted portion of the ABT magma due to the low velocity of volatiles diffusion within a crystallizing magma body
and/or to the short time between volatiles migration and the onset of the eruption. Furthermore, the increased amount of volatiles
in this level of the chamber strongly affected the eruptive behavior. In fact, the emission of these products at the LAG vent,
towards the end of the eruption, modified the eruptive style from classical strombolian to strongly explosive. 相似文献