TIME SCALES AND TEMPERATURES OF CRYSTAL STORAGE IN MAGMA RESERVOIRS: IMPLICATIONS FOR MAGMA RESERVOIR DYNAMICS (Invited Presentation)

The thermal and therefore physical state of magma bodies within the crust control the processes and time scales required to mobilize magmas before eruptions, which in turn are critical to hazard assessment. One notable aspect of Calvin Miller’s career is his ability to make connections between fields and between different perspectives about geologic problems, and this presentation will explore the connections between different approaches to understanding the time scales and thermal conditions of magma storage in crustal reservoirs. Crystal records can be used to reconstruct magma reservoir histories, and the resulting time and length scales are converging with those accessible through numerical modeling of magma system dynamics. For example, crystallization ages of volcanic minerals typically span a range from 10³-10⁵ years of magma presence within a crustal reservoir, and mineral thermometry indicates relatively high temperatures of crystallization. In contrast, diffusion durations are orders of magnitude shorter, indicating that these high temperatures could not have been sustained throughout the crystals’ histories. These observations suggest that the crystal cargoes within erupted magmas are dominantly stored at near- or sub-solidus temperatures, and that final mixing and assembly of erupted bodies was rapid. These observations are difficult to reconcile with some numerical models of magma reservoir dynamics. However, combining crystal-scale observations with models that incorporate grain-scale physics has great potential to further our understanding of magma reservoir processes.