Petrogenesis and eruption dynamics at Hudson Volcano, southern Chile

David Jon Kratzmann, University of Rhode Island

Abstract

Petrogenesis and eruption dynamics at Hudson volcano, southern Chile Hudson volcano is the southern-most volcano of the Chilean Southern Volcanic Zone. There have been at least twelve Holocene to Recent explosive eruptions, the most significant of which were the 6700 years before present (yrs BP), the 3600 yrs BP, and 1991 eruptions. Pre-eruptive storage of the trachyandesite from the 1991 eruption occurred at pressures of ∼1.5–3.0 km depth at 972°C (±26) under water-saturated conditions. Magmas from the 1991 eruption can be related through combined fractional crystallization and magma mixing. An ascending basaltic magma may have intersected the trachyandesitic storage region between 2-3 kilometers depth, partially mixing with and hybridizing the existing magma. The mixing of these two magmas may have triggered the paroxysmal phase of the 1991 eruption. Holocene storage of the trachyandesitic magmas (1991 and 6700 yrs BP events) occurred at depths between 0.2-3.0 km at approximately ∼972°C (±25) with 1-3 wt% H2O in the melt. Pre-eruptive storage of the trachydacitic magma (3600 yrs BP event) occurred between 1.1-2.0 km, at 942°C (±26) with ∼2.5 wt% H 2O. During the Holocene activity at Hudson volcano, mantle-derived magmas stalled within mid to lower crustal levels (∼6-24km). Differentiation to more evolved compositions occurred by crystal fractionation involving a hydrous mineral assemblage that included amphibole. As evolved magmas ascend from depth they cross out of the amphibole stability field and further crystallization involves an anhydrous mineral assemblage and may explain the lack of phenocrystic amphibole in the Hudson samples. The ash tracking model PUFF can successfully reproduce the aerial distribution and evolution of the plumes from the 1991 eruptions. Variations in eruption column height and z-width display the strongest influence on plume shape and evolution, with optimal agreement between simulated and observed plumes occurring when the majority of ash is concentrated at or around the tropopause (∼11 km). The concentration of ash at this level may result from gravitational settling of particles within the umbrella region. The stratigraphic complexity within the 1991 phase II fall deposit may arise from a “wandering plume” that repeatedly crosses the main dispersal axis.^

Subject Area

Geology|Geochemistry

Recommended Citation

David Jon Kratzmann, "Petrogenesis and eruption dynamics at Hudson Volcano, southern Chile" (2009). Dissertations and Master's Theses (Campus Access). Paper AAI3380533.
http://digitalcommons.uri.edu/dissertations/AAI3380533

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