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| Titel |
Timing of magma storage at the Vulcano Island during the last 1000 years |
| VerfasserIn |
Rosanna De Rosa, Paola Donato, Anna Gioncada, Marisa Giuffrida, Eugenio Nicotra, Marco Viccaro |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250122089
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| Publikation (Nr.) |
 EGU/EGU2016-1027.pdf |
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| Zusammenfassung |
| Understanding the nature and timescales of magmatic processes is one of the primary goals of
modern volcanology, and chemical zoning is an efficient tool to achieve this aim. In basic
volcanic rocks, plagioclase is a common phase used for documenting magmatic
processes and their timescales. This is chiefly due to its stability over a wide range of
physical-chemical conditions and its sensitivity to changes in thermodynamic parameters
during its growth in magma storage and transport zones. We present here textural
analysis and major (SEM-EDS/WDS) and trace (LA-ICP-MS) element zoning data on
plagioclase crystals from selected volcanic products of Vulcano (Aeolian Islands),
emitted during the last 1000 years. The collected samples belong to the La Fossa
cone (Palizzi latitic lava flow, latitic enclaves within Commenda and Pietre Cotte
rhyolitic lava flows, 1888-90 spatter bombs) and Vulcanello peninsula (shoshonitic and
shoshonitic-latitic lava flows at the end of Vulcanello I and Vulcanello 3 phases,
respectively).
Textural observations through polarizing optical microscope, high-contrast BSE images
and SEM-EDS/WDS core-to-rim profiles, allowed to discriminate four different
plagioclase textures, namely: 1) oscillatory-zoned crystals; 2) sieve-textured rims;
3) dissolved/resorbed cores; 4) cores with coarse sieve-textures. Plagioclase with
sieve-textured rims and coarsely-sieved cores (Types 2 and 4) are the most abundant in
the analyzed products. The estimates of maximum magma residence time have
been obtained on crystals with exclusive oscillatory-zoned patterns (Type 1) or
portions of crystals not severely affected by μm-sized glass inclusions caused by
disequilibrium. We used one-step modeling of Sr diffusion considering the highest An
content of each crystal and magma temperature ranging between 1075 and 1175˚
C.
Textural observations and core-to-rim profiles on plagioclases show that dynamics of
magma ascent and storage are markedly different at La Fossa and Vulcanello systems.
Transfer mechanisms are however almost unchanged in each system during the considered
timespan. Diffusion modelling gives residence times between 2 and 22 years. The most
striking feature is that residence times are relatively low for the most evolved products
(latites or latitic enclaves), especially at La Fossa eruptive system (2-19 years), with
respect to the less evolved products of Vulcanello (19-21 years). It is worth to note
that these timescales cannot account for the total amount of residence time of La
Fossa magmas within the crust, but they can reflect the storage time of the most
evolved products into the shallowest feeding system. Residence times for Vulcanello
magmas could be related to longer magma storage at intermediate levels of the
plumbing system followed by rapid transfer at the surface prior to the eruption. |
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