1,721,049 research outputs found
The plagioclase as archive of ascent dynamics: the 2001-2006 eruptive period at Mount Etna
No full textSeveral studies are focused on textural and compositional features of plagioclase as an usefull tool to investigate magma chamber processes, ascent dynamics, and physico-chemical conditions. In particular water content, which plays a fundamental role in volcanic process, strongly affects plagioclase stability and, by conseguence, textural and compositional features. However, such reconstruction are usually biased by too many assumptions; particularly when dealing with past eruptions or remote volcanoes. Only few volcanoes provide an array of instrumental monitoring to constrain timing and modality of eruptive events. In this respect Mount Etna probably represents one of the most controlled volcano in the world and a great wealth of seismological and ground deformations data are available. In this work we present a textural and compositional study of plagioclases from lavas emitted during the 2001-2006 eruptive period on Mount Etna. Textural classification has been done on over 130 thin sections taking into account different portion of the crystals. This allow to recognize different types of core (ehuedral and rounded) and rims (dusty or with melt inclusion alignment) separated by oscillatory zoned overgrowth.
Oxygen fugacity in magmas has been calculated using the method of [1] and results has been used to reequilibrate the melts to mantle equilibrium, adding back the appropriate quantity of fractionated material. Water content of the melt has been estimated using the hygrometer of [2]. These data were used in the MELT model to estimate the plagioclase stability field and to calculate theoretic composition at different water content. Results were integrated with monitoring data acquired during the entire period under study with the aim to reconstruct magma ascent and storage conditions, as well as the mechanism of eruption triggering. Results indicate the 2001-2006 eruptive period involved magmas with quite similar major element composition but different dissolved H2O. Complex zoning such as dusty areas and alignments of melt inclusions in outer portion of the phenocrysts suggest two different trigger mechanism respectively: i) magma input and mixing with a more basic and volatile-rich magma; ii) fracture migration that induce decompression of shallow magma batches
Magma mixing during the 2001 event at Mount Etna (Italy): Effects on the eruptive dynamics.
No full textDuring the 2001 eruptive episode three different magmas were erupted on the southern flank of Mount Etna volcano from
distinct vent systems. Major and minor element chemistry of rocks and minerals shows that mixing occurred, and that the mixed
magma was erupted during the last eruptive phases.
The space–time integrated analysis of the eruption, supported by geophysical data, together with major and trace element
bulk chemistry (XRF, ICP-MS) and major and trace mineral chemistry (EPMA, LAM ICP-MS), support the following model:
1) trachybasaltic magma rises through a NNW–SSE trending structure, connected to the main open conduit system; 2) ascent of
an amphibole-bearing trachybasaltic magma from a 6 km deep eccentric reservoir through newly open N–S trending fractures;
3) just a few days following the eruption onset the two tectonic systems intersect at the Laghetto area; 4) at the Laghetto vent a
mixed magma is erupted.
Mixing occurred between the amphibole-bearing trachybasaltic magma and an inferred deep more basic end-member. The
most relevant aspect in the eruptive dynamics is that the eruption of the mixed magma at the Laghetto vent was highly explosive
due to volatile content in the magma. The gas phase formed, mainly because of the decreased volatile solubility due to rapid
fractures opening and increased T, related to mixing, and partially because of the amphibole breakdown.
D 2005 Elsevier B.V. All rights reserved
The contemporaneous emission of low-k and high-k trachybasalts along the ne rift during the 2002 eruptive event (Etna, Sicily)
No full textCan a simple lherzolitic mantle source explain the geochemical variation of Etnean magmas through time?
No full textMagma dynamics as inferred by plagioclase textural and compositional zoning at Mount Etna volcano
No full textThe contemporaneous emission of low-K and high-K trachybasalts and the role of the NE rift during the 2002 eruptive event (Etna, Sicily)
No full textMount Etna volcano erupted almost simultaneously
on its northeastern and southern flanks between
October 27 and November 3, 2002. The eruption on the
northeastern flank lasted for 8 days, while on the southern
flank it continued for 3 months. The northeastern flank
eruption was characterized by the opening of a long
eruptive fracture system between 2,900 and 1,900 m.a.s.l.
A detailed survey indicates that the fractures’ direction
shifted during the opening from N10W (at the NE Crater,
2,900 m) to N45E (at its lowest portion, 1,900 m) and that
distinct magma groups were erupted at distinct fracture
segments. Based on their petrological features, three
distinct groups of rocks have been identified. The first
group, high-potassium porphyritic (HKP), is made up of
porphyritic lavas with a Porphyritic Index (P.I.) of 20–32
and K2O content higher than 2 wt%. The second group is
represented by lavas and tephra with low modal phenocryst
abundance (P.I.<20) named here oligo-phyric (low-phyric),
and K2O content higher than 2 wt% (HKO, high-potassium
oligophyric). The third group, low-potassium oligophyric
(LKO), consists of tephra with oligophyric texture (P.I.<20)
but K2O content < 2 wt%. K-rich magmas (HKP and HKO)
are similar to the magma erupted on the southern flank, and
geochemical variations within these groups can be
accounted for by a variable degree of fractionation from a
single parent magma. The K-poor magma (LKO), erupted
only in the upper segment of the fracture, cannot be placed
on the same liquid line of descent of the HK groups, and it
is similar to the magmas that fed the activity of Etna
volcano prior to the eruption of 1971. This is the first time
since then that a magma of this composition has been
documented at Mt. Etna, thus providing a strong indication
for the existence of distinct batches of magma whose rise
and differentiation are independent from the main conduit
system. The evolution of this eruption provides evidence
that the NE Rift plays a very active role in the activity of
Mt. Etna volcano, and that its extensional tectonics allows
the intrusion and residence of magma bodies at various
depths, which can therefore differentiate independently
from the main open conduit system
Dynamics of magma supply at Mt. Etna volcano (Southern Italy) as revealed by textural and compositional features of plagioclase phenocrysts
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The emission of distinct lavas during the 2002 eruptive event at Mount Etna: inferences on the role of the NE and S rifts in the magma ascent and eruptive dynamics
No full textThe role of tectonics on magma supply and eruptive styles at Mt. Etna during the 2001-2007 period
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