IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4W_1D-P1

Date/Time: July 24 Poster

Magmatic control on volcanic activity at Volcan de Colima, Mexico
Reubi Olivier1 , Blundy Jon2 , Pickles Joe2 , Varley Nicholas3
1

Institut des sciences de la Terre, Universite de Lausanne, Switzerland, 2 School of Earth Sciences,
University of Bristol, UK, 3 Facultad de Ciencias, Universidad de Colima, Colima, Mexico
E-mail: olivier.reubi@unil.chVolcan de Colima historical activity is characterized by periods of intermittent effusive and Vulcanian eruptions
punctuated by major sub-Plinian to Plinian eruptions, the most recent of which occurred in 1913.

Theeffusive-Vulcanian phases are dominated by andesitic lavas with 61 wt% SiO2 , when the Plinian eruptions involve
more mafic andesites with 58 wt% SiO2 . The systematic shifts in compositions associated with the Plinan eruptions
indicate a link between the eruptive cycles and the magmatic dynamics.

Detailed petrological and geochemical investigations of the magmas erupted during the effusive and Vulcanianactivity between 1998 and 2010 enable us to constrain the storage conditions and pre-eruptive evolution ofthese magmas. The melt inclusions exhibit compositional trends consistent with up to 40% crystallization undervapour-statured conditions at pressures <1.5 kbar. Decompression induced dehydration is driving crystallisationin the sub-volcanic magmatic systems. Compositional zoning of phenocrysts indicates that, in addition to magma
mingling in the ascending dacite melt of mafic crystals, magma mixing was important in the 1998-2010 magmatic
system but involved predominantly dacitic magmas with limited compositional variability. The range of (210 Pb/226 Ra)
activity ratios and the width of amphibole reaction rims indicate that the feeding magmatic system comprised
several magma batches with residence and degassing times in the vapour-saturated section of the system ranging
from several days to 7 years. No significant differences in petrology, volatile contents, degassing paths and timescales are observed between the Vulcanian and effusive eruptions, implying that these shifts in eruption style are
principally related to conduit dynamics. The most vigorous effusive phases may, nonetheless, be related to influxof undegassed dacitic magmas.

The last major Plinian eruption, in 1913, erupted magmas clearly distinct from those of 1998-2010 in termsof storage conditions and pre-eruptive magmatic evolution. The most distinctive features of the 1913 magmas
are the higher H2 O contents (and storage pressures) of the melt inclusions, the textural and chemical evidences
for magma mixing with mafic melts shown by some phenocrysts, and the more mafic compositions of thegroundmass glasses compared to the melt inclusions. Taken together this indicates that the Vulcanian-effusive
activity characteristic of the 1998-2010 period and the 1913 Plinian eruption represent clearly distinct pre-eruptive
scenarios rather than a continuum. Influx and mixing of mafic magmas in the dacitic subvolcanic reservoir wasimportant prior to the 1913 eruption and most likely caused the shift in eruptive style. The rates and periodicity ofreplenishment of the subvolcanic system by, respectively, dacitic and mafic magmas appear to be key parameters
controlling the eruptive cycles at Volcan de Colima.

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