UNRAVELING MAGMATIC HISTORIES AT MULTIPLE SCALES
Wallrich, Blake Marshall
In this study, we take a multi-faceted approach to better understand silicic magmatism. The broad questions that we were aiming to address include: (1) How do magmatic systems and silicic magmas evolve through time following supereruptions? (2) Is elemental partitioning in titanite temperature dependent? (3) Can core to rim profiles in crystals provide insight into how late stage silicic melts evolve during the waning stages of magmatism? To address question (1) we investigated post-supereruption silicic magmas that erupted near the source caldera of the Peach Spring Tuff. Glass and phenocryst geochemistry from a suite of post supereruption ignimbrites suggest a transition from cool-wet-oxidizing to hot-dry-reducing magmatic conditions over a ~240 ka period. To address questions (2) and (3) we investigated elemental partitioning between titanite and melt by collecting geochemical analyses of the titanite rims and coexisting glass from a variety of different samples. Our results suggest variation (factor of 2) in partitioning over ~100 ¬ºC; higher partition coefficients were observed with decreasing temperatures (as recorded by zircon saturation and Zr-in-titanite thermometers). Core to rim transects using the temperature-dependent partitioning model suggest some titanite grains experienced complex crystallization histories, and others experience simple down temperature crystallization histories.