The processes controlling the evolution of magmas (molten rock) in the Earth's crust are important as they control the behavior of volcanoes, and so condition the atmosphere and biosphere. Understanding the timescales and range of process that can produce a specific type of eruption or composition has been difficult, as magma reservoirs are not directly observable. Hence it is necessary to infer their behavior by studying natural examples that are the products of volcanic eruptions. But this information appears only as distinct ''snapshots,'' and so difficult to understand as the result of a continuous process, or set of linked processes. This project will provide a more complete picture of these processes by combining a forensic approach using field and lab data from a particular eruption, with computer models of magma processes that can link the snapshots into a continuous ''movie'' of what happens in the subsurface. Geologists will then better understand how any characteristic snapshot arises, and how to better infer unseen process that shape the upper portion of Earth.
The approach to be used is to obtain U-series disequilibria data in conjunction with trace-element diffusion to identify the time scales of particular events in the magma reservoirs. The investigators will also measure major- and trace-element profiles across mineral grains to identify chemical signatures of magmatic processes. When combined, these data can provide a schedule of events that have happened in the magma reservoir. The overarching goal is to identify and distinguish the fundamental classes of physical processes that produce the chemical and textural diversity in crystals measured in the erupted products. In this study, they will be able to address part of this larger question by examining to what extent the chemical zonation in crystals requires open-system processes as opposed to simply gathering crystals from different regions of a closed-system magma reservoir. In order to do that, they will conduct an integrated numerical and geochemical study to (1) develop numerical models that track the response of active (smart) crystals to chemical and physical changes in their magmatic environment, and (2) compare the resulting synthetic crystal data to measurements of crystals in a natural example at Volcn Quizapu in Chile. Combining these two approaches allows for specific predictions to be made that can be independently tested by looking at the progressive changes in the chemistry of the magmatic products erupted from the deeper reservoirs.
