Constraining the heat transfer from convecting upper-crustal magma reservoirs to hydrothermal fluid flow systems

Heat transfer through the upper crust is primarily controlled by magma flow, heat conduction and hydrothermal fluid flow. The interplay between magma and fluid flow processes is essential for geothermal systems, ore formation and volcanic processes, but is not well constrained due to a lack of accessibility. We developed a coupled numerical model that can resolve both magma and hydrothermal flow to quantify the influence of magma convection and rock permeability on heat transfer. The results demonstrate how magma convection enhances the energy transfer towards the magma-hydrothermal interface, leading to an accelerating effect of up to 15% on the cooling of the reservoir. However, at high brittle-ductile transition temperatures and high host rock permeabilities, magma flow can also prevent efficient permeability creation and entrainment of hydrothermal fluids at the edges of the reservoir, leading to a secondary decelerating effect on the cooling rate. Using different initial melt compositions (basaltic to rhyolitic), our numerical simulations can further constrain the varying timescales of magma evolution from shorter-lived, lower-crystallinity convecting magma reservoirs to longer-lived, higher-crystallinity magma mushes where convection has seized.