ABSTRACT

The processes involved in formation and storage of magma within the Earth's upper crust are of fundamental importance to understanding volcanoes and volcanic hazards. Previous NSF-supported research by two of the PIs showed that at Mount Hood, Oregon, only a small fraction (most likely less than 1%) of the total time that magma is stored underground is spent at high enough temperatures that would allow magma to be easily mobilized and erupted. Partial data sets for other volcanoes suggest that these conditions are widespread, but this remains to be tested. This new project will address the questions of whether magmas in general are subject to similar storage conditions as those seen at Mount Hood, and what are the fundamental controls on the processes of magma storage underneath volcanoes. The project will address these questions using geochemical measurements of crystals that grew beneath the surface and will provide information on the duration and temperature of magma storage. These results will be combined with advanced computer models of magma chambers to explore the interplay of magma addition, heat loss and changes in magma composition. In addition to contributions to the science of volcanology and geochemistry, the work will have impacts in understanding volcanic hazards - in particular, the percentage of time that different magma bodies spend in an eruptible state (and, critically, the processes that control that percentage of time) will provide insight into the hazard represented by different volcanoes and will also provide a better context to interpret the results of seismic imaging or other remote-sensing applications. This project will contribute to training the next-generation STEM workforce by providing support for a postdoctoral researcher and three graduate students, one at each institution. At OSU and at UCD undergraduates will also take part in the research.

This project will integrate observational data with numerical modeling for selected volcanic systems, to address the broader question: "What are the thermal and physical conditions of magma storage in the Earth's crust, and what are the primary controls on those conditions?" This project will build on our results for Mount Hood and on existing partial data sets by exploring two high-priority specific questions that pertain to the maturation of magmatic systems: 1) What is the role of volume of the shallow reservoir? How do magma storage conditions vary over erupted volumes of <1 to >10 km3? and 2) What is the role of composition? Is there a difference between the thermal history of magma storage in dacitic and rhyolitic systems? The results of this project will provide some of the first observational data on the thermal histories of magma storage, and the numerical modeling will allow us to put these results into a generalizable thermodynamic framework. These results will provide a critical, observation-based understanding of the physical conditions of magma storage, which in turn will provide a better understanding of magma reservoir processes. Ultimately we will build a framework in which to understand various aspects of crystal records such as the interpretation of mineral thermobarometry, textural information, and time scales captured by mineral zonation. The results of this project will have broad implications within the field of igneous petrology/geochemistry by providing a conceptual framework for the processes that operate within magma reservoirs - and crucially, the time scales relevant to the different processes.

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