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Sean Carney Thesis Defense

September 9 @ 3:00 pm - 5:00 pm MDT

Sean Carney in the field

Investigating the petrogenesis and mineral chemistry of the only recorded Plinian dacite eruption at Llaima volcano, southern Chile

Llaima volcano, located in the Andean Southern Volcanic Zone (SVZ) 82 km east of Temuco, Chile, is one of the largest and most active volcanoes in the region. Throughout Llaima’s post glacial period (~13.5 ka; Naranjo and Moreno, 1991; Naranjo and Moreno, 2005) the composition of eruptive deposits has been dominated by basalt to basaltic andesite. However, at ~10 ka a Plinian eruption produced a dacitic pumice (called Llaima Pumice; De Vleeschouwer et al., 2005) that is capped by andesitic pumice (Schindlbeck et al., 2014). While several studies briefly discussed the Llaima Pumice and andesite cap (Naranjo and Moreno, 1991; De Vleeschouwer et al., 2005; Schindlbeck et al., 2014), there have been very few investigations that have focused in detail on the petrogenesis of this dacitic eruption (De Vleeschouwer et al., 2005).

The outstanding goal of this thesis will be to investigate the origin of the most evolved magma produced at Llaima volcano, the Llaima Pumice, along with the andesite cap. Major and trace element contents from whole rock and glass analyses will be used to determine how compositions vary throughout the eruptive sequence. Whole rock compositions in combination with mineral phase chemistry will be used to investigate the roles of magma recharge and mixing during the eruption, with a particular focus on the relationship between the dacite and the andesite cap. Mineral thermobarometry will be used to determine pre-eruptive storage conditions of both units. Finally, all geochemical data will be incorporated into petrologic models to determine the roles of fractional crystallization and magma mixing prior to and during the eruption. Understanding the processes that allowed for the formation of the dacitic Llaima Pumice in a dominantly mafic system will help to better understand the evolution of the post-glacial volcanic system.

Advisor: Dorsey Wanless

Co-Advisors: Brittany Brand, Mark Schmitz

When: Wednesday, September 9, 2020
Time: 3:00 PM
Where: Zoom