Deep Coupling Between Geothermal and Magmatic Systems: Insights from Numerical Models

Hydrothermal systems receive heat and volatiles from deep magma bodies. Under certain conditions, these magma bodies can evolve to an unstable, overpressured state and erupt. Studying how these two systems are coupled can help us understand near surface observations and the historic eruption record, and optimize our usage of geothermal resources. In addition, learning about eruptive triggers has implications for our understanding of volcanic hazard. This is applicable in numerous regions such as the Taupo Volcanic Zone (hereafter TVZ) in New Zealand. We introduce a simple model where a magma chamber is cooled by an overlying geothermal system and recharged by a deeper magma source. The model tracks changes in pressure, mixture enthalpy and composition, and implements parameterisations of eruption, hydrothermal cooling, viscoelastic relaxation, and volatile leakage. The thermodynamic properties of the melt, crystals and water are computed using rhyolite-MELTS. In this paper, we present the implementation of the model and then investigate the principle differences between magma bodies with and without overlying geothermal systems. We observe three eruption regimes depending on the strength of hydrothermal cooling: (i) no eruption, (ii) recharge driven eruptions, and (iii) a combination of recharge and cooling driven eruptions. Finally we investigate the influence of competing processes on the evolution of the thermodynamic properties and composition of the magma chamber in the case of the TVZ. We use existing literature on the region to choose the initial parameters.