EAR-PF: Resolving the tempo of edifice development and rhyolite formation in a large-caldera system, Atitlan, Guatemala

Cunningham Heather S, Pittsford NY

Investigators

Abstract

Dr. Heather S Cunningham has been granted the NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at the University of Wisconsin - Madison. The investigation aims to detail the short- and long-term trends in caldera edifice development at Atitlán Caldera, Guatemala. Selected volcanic ash and lavas representing the large silicic eruptions, associated scoria layers and cone-growth phases will be collected during a field campaign for geochemical analysis. Major and trace element data will be integrated into petrologic models to determine how large silicic magma bodies develop and if they are related by shallow-level modification processes such as fractional crystallization, magma mixing or assimilation. Isotopic data (87Sr/86Sr and 143Nd/144Nd) will be measured to support petrologic models since these isotopic ratios are distinctive to source composition. To constrain eruptive age, 40Ar/39Ar isotopes will be analyzed on phenocrysts in distinctive eruptive units. 230Th/238U disequilibrium will be measured on volcanic ash to resolve whether large silicic bodies are rapidly differentiated from a homogeneous source, such as a deep crustal hot zone, formed by the coalescence of several magma bodies or the product of crustal assimilation. By resolving the time scales and processes that lead to large-caldera eruptions and associated cone-building phases potential volcanic risk can be inferred. However, our understanding of the processes that lead to large caldera-forming eruptions is limited by the lack of recent, well-exposed deposits. Thus, the Atitlán volcanic complex is ideally suited to test conflicting models for the generation of large-volume silicic eruptions and more importantly time scales over which caldera-systems develop. In addition to the development of geochemical models, an educational exercise will be created. A Dynamic Digital Map of Atitlán Caldera will be made available to educators that will allow students hands-on access to real world data.