Coupling magma ascent models with volatile diffusion chronometry

Abstract

The pre- and syn-eruptive magma decompression rate is recognized as a key parameter modulating eruption dynamics, with explosive eruptions being generally associated with much larger decompression rates than effusive ones. Magma decompression rates cannot be directly measured and thus are typically inferred from petrological, geochemical, numerical modelling, and seismic data. Most studies use petrological information of volatile element diffusive equilibration in glass and crystals to infer a single value for the magma ascent rate for a given eruption, even though numerical volcano conduit simulations show that changes of velocity are expected during magma ascent. Here we integrate magma ascent conduit models with diffusion chronometry of volatiles in melt embayments and phenocrysts to obtain a more comprehensive understanding of magma ascent rates. We find that incorporating a more realistic boundary condition that depends on the magma ascent path with variable velocities gives time estimates that can be up to a factor of 7 longer than from the standard assumption of constant magma ascent rate. Therefore, previous magma ascent rates from diffusion chronometry of volatiles in crystals and melts with a fixed boundary condition may be significantly overestimated. Overall, we show that coupling of magma ascent models with diffusion chronometry can provide more robust inferences of magma ascent and thus improve the understanding of the role of this parameter into the explosive and effusive eruption controls.