Post-glacial magma dynamics at the Mocho-Choshuenco volcanic complex, Chile

"Most subaerial volcanism on Earth occurs at volcanic arcs, where the most explosive volcanoes are found. The growth of an arc volcano is ultimately driven by magmatic processes occurring in the subducting slab and sub-arc mantle, however, over timescales of 10s-100s of kyrs, magma ascent and eruption can be influenced by factors such as lithospheric tectonics or glacial activity. Understanding the growth and eruptive history of these volcanoes therefore requires understanding arc magmatism within the context of both regional geodynamics and other factors that may modulate eruptive activity.

The Mocho-Choshuenco volcanic complex, located in Chile's southern volcanic zone, has a history of frequent explosive eruptions1. Lava and tephra compositions vary from basaltic to rhyolitic, and magmas are erupted from a variety of vents, including numerous monogenetic cinder cones. Recent research2 suggests that glacial activity associated with ice removal after the last glacial maximum (at 18 ka) exerted a strong control on erupted compositions from Mocho-Choshuenco. The proposed response of this volcanic system to ice removal is more nuanced that previously suggested for arc volcanoes3 and involves transitions in the dynamics of crustal melt storage as the sub-volcanic plumbing system responds to the stress changes associated with unloading. Investigating the role climate variability in modulating volcanism at Mocho-Choschuenco, and the potential implications for factors such as the flux of volatiles to the atmosphere, requires detailed characterization of the source(s) and storage histories of key post-glacial eruptive units. A further factor influencing eruptive activity here is the presence of a large strike-slip fault system: the Liquine-Ofqui fault zone. This large-scale intra-arc structure interacts with volcanism along the southern volcanic zone4 and at Mocho-Choshuenco appears to facilitate the ascent and eruption of unusual melt compositions not observed at the main eruptive vents5.

This project will apply geochemical, petrological, and isotopic methods to investigate the dynamics of magma supply and storage at Mocho-Choshuenco volcanic system during the post-glacial period. You will undertake fieldwork in Chile to sample key eruptive units, gaining skills in field sampling in volcanic terrains. You will then design and implement an analytical programme aimed at investigating the sources of magmas sampled from different eruptions and reconstructing pre-eruptive storage dynamics and volatile fluxes. Glass and mineral composition will be analysed via electron microprobe and, if suitable samples are found, an application made to collect data on volatile contents at the NERC Ion Microprobe Facility. In parallel, an investigation of any variations in mantle source parameters, associated with either tectonic or glacial controls on magmatism, will be investigated by analysis of radiogenic isotope ratios via thermal ionization mass spectrometry (TIMS) at Leeds. The results of the geochemical analysis will be integrated to construct models of magmatic processes at Mocho-Choshuenco using either available petrological modelling tools or other numerical methods.





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