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Quantifying mass and heat transport by hydrothermal fluid flow in a caldera setting

Jonas Köpping , Thomas Driesner

Abstract

Hydrothermal systems in caldera settings are potential targets for geothermal energy production. Increased permeability within the bounding ring fault that confines the caldera may represent preferred fluid flow pathways. To explore the spatio-temporal evolution of mass and heat transport within both the ring fault and the caldera infill, we conducted three-dimensional numerical simulations of hydrothermal fluid flow in the vicinity of a cooling magma chamber emplaced at 3 km depth. A cone-shaped, inwardly dipping high-permeability zone located above the intrusion represents the bounding caldera ring fault. Our results show that ~20--30 % of the total energy transport to shallow depths <1.5 km is accommodated by the high-permeability ring fault. This fault-focused energy transport occurs over a relatively short timescale (~5 kyrs) when the cooling magma chamber feeds hot fluids directly into the fault plane, leading to near-surface boiling zones. With increasing magma cooling and an associated shrinking heat source, upflow zones shift towards the caldera centre forming a hydrothermal plume. This plume accommodates ~60--70 % of energy transport to shallower depths <1.5 km over the first ~20--30 kyrs model time. Preliminary results indicate that energy released from the crystallised magma chamber remains stored within the geothermal reservoir at greater depth and is gradually transferred towards the surface via hydrothermal convection, forming a long-lived geothermal system. Our simulations suggest that ring faults can be key structures that transiently localise increased mass and heat transfer over a hundreds of years period, however, they may become less significant on geological timescales.