Numerical modeling of zircon age populations in a periodically rejuvenated silicic magma mush

Abstract:

In order to accurately interpret and forecast hazardous volcanic processes such as ash columns, lava flows, and lahars, a sound interpretation of the magma body – e.g., volume; longevity; proportion of solids, melts, and fluid; chemical composition; and temperature – is necessary. One way to aide volcanic hazard assessment is studying past eruptive behavior, which includes understanding the state of the magma system, such as unrest and magma accumulation, prior to eruptive events. We focus on parallel magma dynamics and geochronological modeling of zircon crystal growth that provides a temporally-constrained window into the thermal and chemical evolution of a magma system. While zircon geochronology and thermometry have been extensively studied and the spatial resolution and precision of dating methodology are constantly improving, questions remain about the range and timescales of physical processes that can be recorded by zircon crystals and how dutifully they record the entire thermal and rejuvenation history of these bodies. As such, we turn to numerical modeling to better constrain the interpretation of zircon ages to infer magmatic processes. Within a 3D multiphase (crystal + melt), thermal, and mechanical magma dynamics model, we create a long-lived magma mush and enact a variety of periodic magmatic intrusions. The local chemical and thermal conditions in this model are used to model zircon saturation and growth rate, thereby coupling reservoir-scale and crystal-scale models. This project seeks to investigate how high frequency intrusion events in a mushy silicic magma system effects the zircon populations of the erupted and residual magma, particularly in the context of small volume but frequently erupting systems. Additionally, we ask if the zircon age populations can indicate specific magmatic processes such as recharge, eruption, or stalling events, and we discuss these in the context of Mt St. Helens, WA and Three Sisters, OR. Overall, this data will provide insight into improving the interpretation of zircon ages from natural samples with respect to distinct events in the magmatic system.