The Roles of Heat and Gas in a Mushy Magma Chamber

Abstract

Crustal magmatic systems likely consist of magmatic reservoirs dominated by crystal mush. Recent studies suggest that the physical processes occurring in crystal mush could alter the response of magmatic reservoirs during volcanic unrest. Here, we present a magma chamber deformation model that incorporates two new aspects in crystal mush: heat and exsolved gas. The model is based on earlier studies by Liao et al. (2021) with additional processes including thermal-mechanical coupling, dependence of material properties on gas content, and temperature evolution following an injection of hotter magma. The post-injection time-dependent evolution of the system can be grouped into three periods, which are dominated by poroelastic diffusion (short term), viscoelastic relaxation (mid term), and thermal equilibration (long term). All three time-regimes are strongly affected by gas distribution, which alters the relative compressibility of the crystal-rich and crystal-poor regions in the chamber. The contribution of thermal evolution emerges during the mid-term evolution. The time-dependent evolution of the system highlights the intrinsic ability of a gas-bearing mushy magma chamber to generate non-monotonic time series of stresses, deformation, and magma transport.