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| Titel |
Laguna del Maule magma feeding system and construction of a shallow silicic magma reservoir |
| VerfasserIn |
Francisco Cáceres, Ángelo Castruccio, Miguel Parada, Bettina Scheu |
| 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 |
250146483
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| Publikation (Nr.) |
 EGU/EGU2017-10511.pdf |
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| Zusammenfassung |
| Laguna del Maule Volcanic Field is composed by at least 130 basaltic-to-rhyolitic eruptive
vents that erupted more than 350 km3 of lavas and pyroclasts since Pleistocene in the Chilean
Andes. It has captivated attention because of its current high accelerated uplift suggested to
be formed by a growing shallow rhyolitic magma reservoir beneath the zone of deformation.
Studying six Holocene post-glacial andesitic-to-rhyolitic lavas and one dome that
partially overlap the ground-inflation zone, we determined the architecture and
steps of construction of the magma feeding system that generated its post-glacial
effusive volcanism. Further we suggest a possible origin for the rhyolitic magma that
generated the ring of rhyolites encircling the lake and remain active causing the
uplift.
Mineral chemistry and textures suggest the same provenance of magma for the studied
units, as well as complex magmatic history before eruptions. Similar temperatures, pressures,
H2O and fO2 conditions for amphibole crystallisation in first stages indicate a common ∼17
km deep original reservoir that differentiated via in-situ crystallisation. The chemistry
of the amphiboles present in all not-rhyolitic units shows trends that indicate a
temperature domain on their crystallisation over other thermodynamic parameters
such as pressure, water activity or chemistry of co-crystallising phases. All this
supports a mush-like reservoir differentiating interstitial magma while crystallisation
occurs.
P-T conditions for amphibole crystallisation indicate that only amphiboles from
rhyodacites show a non-adiabatic decompression that give rise to a polybaric and polythermal
evolution trend from ∼450-200 MPa and ∼1030-900 ˚ C. In addition, unbuffered fO2
conditions were calculated for rhyodacite amphibole crystallisation upon cooling from melts
with rather constant H2O contents. We propose that a large part of these rhyodacite
amphiboles were formed during a non-adiabatic magma ascent similar to that expected for
within-reservoir convective plumes that interact with surrounding cooler and more
differentiated melts. Rhyolites appear to be unrelated to the evolution of rhyodacitic magma
because they crystallised under buffered and less oxidizing conditions. This along
with plagioclase patterns is in agreement with inputs of slightly hotter rhyolitic
magma with no significant chemical difference that formed a zone of rhyolitic magma
accumulation. This is consistent with the absence of mafic enclaves in the studied
rhyolites.
However, eruptions of andesitic-to-rhyodacitic lavas were triggered by injections of
different more primitive magma batches into a mush-like reservoir stalled at different depths.
Likewise, ascent of magma from a deeper to a shallower level would also be conducted by a
more primitive magma recharge as it is suggested by the presence of mafic enclaves and
complex zonation and textures of plagioclases in these lavas. Here constant input of
hotter and more primitive magmas enables the system to remain active in time. In
the case of the rhyolitic units, the silicic reservoir receives constant input of the
extracted interstitial rhyolitic magma from a deeper level of the mush-like reservoir. |
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