Effects of H2O-CO2 mixtures on eruption cycles in shallow magma reservoirs

Volatiles exert a strong control over the chemical and mechanical evolution of shallow magma reservoirs. Previous studies showed that volatiles are a key control on chamber stability and consequently eruption frequency and volume. However, these previous approaches have focused on volatile phases composed entirely of water. While water is the most abundant volatile species in magmas, the amount of carbon dioxide present in the system can significantly affect the behavior of silicic magmas. For example, carbon dioxide has different thermal properties than water and decreases the solubility of water. As a result, CO₂ has an impact on the energy budget, the melting curve, and the amount of volatiles exsolved in a magma chamber at a given pressure and temperature. Here, we propose an expansion to the model proposed by Degruyter and Huber (2014), where new equations for the conservation of CO₂ in the magma are derived. The updated model offers a better understanding of how different mixtures of H₂O-CO₂ in magmas affect eruption frequency and volume for magma chambers subjected to various rates of recharge.