Investigating the Impact of an Exsolved H<sub>2</sub>O‐CO<sub>2</sub> Phase on Magma Chamber Growth and Longevity: A Thermomechanical Model
K. J. Scholz, Meredith Townsend, Christian Huber, Juliana Troch, Olivier Bachmann, Allie N. Coonin
Abstract
Abstract Magmatic volatiles drive pressure, temperature, and compositional changes in upper crustal magma chambers and alter the physical properties of stored magmas. Previous studies suggest that magmatic H 2 O content influences the growth and longevity of silicic chambers through regulating the size and frequency of eruptions and impacting the crystallinity‐temperature curve. However, there has been comparatively little exploration of how CO 2 impacts the evolution of magma chambers despite the strong influence of CO 2 on H 2 O solubility and the high concentrations of CO 2 often present in mafic systems. In this study, we integrate the thermodynamic effects of dissolved and exsolved H 2 O and CO 2 with the mechanics of open‐system magma chambers that interact thermally and mechanically with the crust. We applied this model to investigate how intrinsic variations in magmatic H 2 O‐CO 2 content influence the growth and longevity of silicic and mafic magma chambers. Our findings indicate that even with a tenfold increase in CO 2 content (up to 10,000 ppm), CO 2 plays a minimal role in long‐term chamber growth and longevity. While CO 2 content affects the magma compressibility, the resulting changes in eruption mass are balanced out by a commensurate change in eruption frequency so that the time‐averaged eruptive flux and long‐term chamber behavior remain similar. In contrast, H 2 O content strongly influences chamber growth and longevity. In silicic systems, high H 2 O contents hinder magma chamber growth by increasing the total eruptive flux and steepening the slope of the crystallinity‐temperature curve. In mafic systems, high H 2 O contents promote magma chamber growth by flattening the slope of the crystallinity‐temperature curve.