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| Titel |
Relationship between the fractal dimension of the enclaves and the volumes of magmas in Montaña Reventada (Tenerife) |
| VerfasserIn |
Helena Albert, Diego Perugini, Joan Martí |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086788
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| Publikation (Nr.) |
 EGU/EGU2014-714.pdf |
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| Zusammenfassung |
| The volcanic unit of Montaña Reventada is an example of magma mixing in Tenerife (Canary
Islands, Spain). The eruptive process has been detonated by a basanite intruding into a
phonolite magma chamber. This eruption started with a basanite followed by a phonolite.
Montaña Reventada phonolite is characterized by the presence of mafic enclaves.
These enclaves represent about the 2% of the outcrop and have been classified
like basanites, phono-tephrite and tephri-phonolite. The enclaves have different
morphologies, from rounded to complex fingers-like structures, and usually exhibit cuspate
terminations.
This study aims to provide a new perspective on the 1100 AD Montaña Reventada
eruption quantifying the textural heterogeneities related to the enclaves generated by the
mixing process. The textural study was carried out using a fractal geometry approach,
and its results were used to calculate some parameters related to magma chamber
dynamics.
Photographs of 67 samples were taken normal to the surface of the enclaves with the aim
of delineating the contact between the enclaves and the host rocks. The resulted pictures were
processed with the NIH (National Institutes of Health) image analysis software to generate
binary images in which enclaves and host rock were replaced by black and white
pixels, respectively. The fractal dimension (Dbox) has been computed by using the
box-counting method in order to quantify the complexity of the enclaves morphology.
Viscosity ratio (μR) between the phonolite and the enclaves has been calculated as
follows:
log(μR) = 0.013e3.34Dbox
PIC
The viscosity of the enclaves has been calculated according to the μRvalue with the
higher frequency and to the calculated viscosity of the phonolite between 900°
and 1200°. We hypothesized that this value corresponds to the amount of mafic
magma present in the system, while the other values represent different degrees
of mingling and chemical diffusion. Viscosity of the basanite can be computed
like:
μenclave = (%phonolite *μphonolite)+ (%basanite *μbasanite)
PIC
μenclaves–-(%phonolite *μphonolite)
μbasanite = %basanite
PIC
The minimum percentages which satisfy the relation are 69.5% of basanite and 30.5% of
phonolite. Although the amount of mafic magma reaches the 69.5%, the presence of enclaves
in the phonolite is just the -1% and the amount of basanite erupted before could correspond
to the 15% of the phonolite (estimated from stratigraphic sections). Probably a magma body
of basanite was still stored in the magma chamber. The volume of basanite still stored during
this time may have evolved to a more explosive magma and hence increases the volcanic risk
in the area. |
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