Basalt and Andesite Magma Storage and Evolution in Puyehue Volcano (40.5 °S), Chile

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Abstract: The study of magmatic processes and their location in the crustal profile is fundamental for the understanding of the volcanic systems and their associated hazards. Changes and continuities in magma storage zones, fractional crystallization and crustal contamination are studied over a time span of 300 ka in Puyehue Volcano in the Southern Volcanic Zone, Chile. Using thermobarometric models outlined in Putirka (2008), bulk assimilationand fractional crystallization modelling this study show that: a) fractional crystallization of plagioclase and clinopyroxene in Puyehue Volcano occurs in the upper 20 km of the crust with plagioclase preceding clinopyroxene in the crystallization sequence, b) fractional crystallization of basaltic andesites is dominated by plagioclase with a break in th e geochemical trend at around 55 wt% SiO2caused by an increased share of pyroxene fractionation and the onset of significant magnetite fractionation, c) both old and young Puyehue volcanics are contaminated by a gabbroic lithology of the lower crust as suggested previously by Jicha et al. (2007) and d) the Anticura Group lavas and a single Puyehue Volcano sample reflect magma-metasediment interaction with likely in the middle to upper crust.

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