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| Titel |
Petrological and geochemical constraints on the recent increase in explosive activity at Santiaguito volcano, Guatemala |
| VerfasserIn |
Paul A. Wallace, Sarah Henton De Angelis, Silvio De Angelis, Jackie E. Kendrick, Adrian J. Hornby, Oliver Lamb, Felix W. von Aulock, Anthony Lamur, Gustavo Chigna, Andreas Rietbrock, Donald B. Dingwell, Yan Lavallée |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138420
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| Publikation (Nr.) |
 EGU/EGU2017-1426.pdf |
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| Zusammenfassung |
| The ability to forecast rapid changes in eruption style at highly active and dynamic volcanic
systems is a fundamental aim for many geoscientists. Over the past century, Santiaguito’s
eruptive longevity of regular, small-to-moderate explosions (typical of dome-building
episodes) have made it the ideal laboratory for the study of eruption dynamics. In 2015 this
activity shifted to more violent, less regular explosive activity, potentially marking the onset
of a renewed and recharged magmatic source. This study presents a unique, high resolution
petrological and geochemical dataset using ash samples collected across this transition
period, revealing detailed insights into the cause behind this rapid change in activity.
Ash and bombs erupted between December 2015 and June 2016 are two-pyroxene
andesites with whole-rock chemistry that is consistent with a long term trend towards
more mafic material (Harris et al., 2003). Furthermore, although bulk chemistry
is becoming more mafic, matrix glass compositions are the most evolved in all
of Santiaguito’s history. Despite this historical trend, the activity in early 2016
showed a rapid increase in bulk SiO2 (∼2 wt.%). The presence of xenocrystic olivine
(Fo68−77) mantled by orthopyroxene (En69), a combination of normal and reverse zoned
plagioclase phenocrysts (up to An91) and the majority of amphibole phenocrysts
completely broken down to pseudomorphs provide strong evidence for a system in
an advanced state of disequilibrium. Magma source conditions from amphibole
suggest depths of ∼17-24.5 km and temperatures of ∼960-1010˚ C. Although depths
are consistent with previous work (Scott et al., 2012), the data suggests elevated
temperatures in the source region, a possible consequence of magmatic recharge. Through
studying amphibole reaction rims, experiments suggest decompression alone would
not be feasible to generate the textures recorded, thus providing evidence for a
complex thermal and chemical history of the magma during pre-eruptive storage and
ascent. Textural and micro-petrological variations have also been investigated to
constrain pre-eruptive conduit conditions, focusing on microlite characteristics
that facilitate assessment of crystallisation processes in the shallow conduit and
magma ascent rates prior to eruption. Our data is complemented by geophysical
observations recorded over the same period, providing further insights into eruption
dynamics. This collaborative work not only captures unique observations of the
on-going dynamic activity at Santiaguito, but aids in deciphering the complexities
associated with transitions in eruptive behaviour for many active silicic volcanoes
worldwide.
Harris, A.J.L., Rose, W.I., Flynn, L.P., 2003. Temporal trends in lava dome extrusion at
Santiaguito 1922 – 2000. Bull. Volcanol. 65, 77–89.
Scott, J.A.J., Mather, T.A., Pyle, D.M., Rose, W.I., Chigna, G., 2012. The magmatic
plumbing system beneath Santiaguito Volcano, Guatemala. Journal of Volcanology and
Geothermal Research 237–238, 54–68. |
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