The Dynamics of Mixed Fluid Bubble Growth and its Effect on Magma Compressibility

For decades, workers have posited second-boiling (the near solidus exsolution of volatiles) as a potential eruption trigger. The mass fraction of exsolved gas has a first order effect on a magma's compressibility. Therefore, volatile exsolution has a profound effect on stresses exerted on the surrounding host rock. Here we model the thermal evolution of a crustal silicic magma chamber and the degassing of a multi-component system. The thermal model is coupled to rhyolite-MELTS. This allows us to track the system's compositional evolution and calculate the H 2 O-CO 2 mixed fluid solubility. The solubility model is used to simulate volatile exsolution through diffusive bubble growth. Here, we modify the approach developed by Proussevitch et al. (1993): bubble growth is governed by disequilibrium between the pressure within pre-nucleated bubbles and the fluid saturation pressure. Simulating volatile exsolution through the kinetics of bubble growth provides a framework to analyze temporal volume and compressibility variations associated with second-boiling. Modeling the system's temporal evolution allows us to examine the effect bubble growth has on stress states around silicic reservoirs.