Magma convection favors ephemeral melt-rich bodies within mushy reservoirs

Magma convection is a mechanism that greatly enhances heat transfer from mobilizable, crystal-poor magma bodies to the surrounding immobile, crystal-rich mush reservoir of Earth's igneous systems. As most of these systems are geophysically shown to be mush-dominated, magma convection is often omitted from thermo-kinetic models, and its role in magma evolution and eruptibility remains underexplored. Here we present 2-D numerical thermal modelling that parameterizes magma convection through a Nusselt-number approach that describes the local enhancement of heat transfers, and examine its effects in the axial mush zone of fast-spreading mid-ocean ridges. We demonstrate that magma convection, while not affecting the overall thermal regime of the mushy reservoir, significantly reduces the lifespan of individual pockets of eruptible melt to <2 years, which is two orders of magnitude shorter than in simulations without convection. Our models also show that magma convection could promote mush reheating and unlocking, potentially participating to the geochemical homogenization of heterogeneous melts extracted from the mantle. Predicted fluctuations in the occurrence and persistence of magma bodies provide insights into their highly transient nature, enhancing our ability to interpret geophysical snapshots of magma-mush systems in oceanic settings, and in other igneous systems.