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

The majority of subaerial volcanism on our planet occurs at volcanic arcs, where Earth’s 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 and glacial activity. Understanding the growth and eruptive history of these volcanoes therefore requires studying 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 magma compositions from Mocho-Choshuenco. The response of this volcanic system to ice removal appears to be more nuanced that previously suggested for arc volcanoes3 and involves transitions in the dynamics of crustal melt storage as the sub-volcanic plumbing system responded to the stress changes associated with unloading. 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.

Mocho Choshuenco volcanic complex, S. Chile. source: https://www.flickr.com/photos/ccordova/477994804/

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.

Basaltic tephra deposits erupted from mafic cones around Mocho Choshuenco, from Rawson (2015)

Within the School of Earth and Environment at Leeds there is the opportunity to engage with researchers in the volcanology, geochemistry, tectonics, and environmental research groups, as well as the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET). The student will also have access to a broad range of Faculty- and University-led training courses and workshops at Leeds (http://www.emeskillstraining.leeds.ac.uk/) and engagement with researchers in Oxford and Chile where co-supervisors/project partners are based.

References

  1. Rawson et al. 2015 JVGR 299, 103-129
  2. Rawson et al. 2016 Geology 44, 251-254
  3. Huybers & Langmuir 2009 EPSL 286, 479-491
  4. Cembrano & Lara 2009 Tectonophys. 471
  5. Rawson et al. 2016 EPSL 456, 66-77