Modeling Melt Migration in the Lithosphere and Asthenosphere of Io, with Applications to Heat Pipe Evolution and Cyclical Volcanism

Due to intense tidal stresses, the interior of Jupiter's moon Io generates heat beyond what would be expected of a body its size. This heat possibly maintains up to ~30% melt in the asthenosphere of Io. Thermal emission data suggests that the majority of heat transport to the surface occurs via advection of this magma through the lithosphere in deep rooted vents known as heat pipes. Although melt segregation appears to be the main heat transfer mechanism on Io, previous studies have not directly modeled the behavior of melt in the asthenosphere and lithosphere of Io.

Using the ASPECT finite element code, we have created a model simulating melt behavior (two-phase flow) in a convecting, molten asthenosphere and a cold, rigid lithosphere. Constant heating is included to represent tidal heating, and a downward surface velocity is included to represent resurfacing. 15 km wide high temperature anomalies representing heat pipes are placed every 260 km in the lithosphere to provide a conduit for initial melt escape.

For the first 400,000 years of the model run, initial perturbations rise and generate melt in the deep mantle. This melt collects against the base of the lithosphere, where melt content can reach ~5% locally. After 400,000 years, the base of the lithosphere begins to heat up due to conduction and shear heating, and viscosity is reduced. Delamination occurs as dense, solid downwellings initiate from the reduced viscosity lithosphere material. These downwellings then heat, partially melt, and rise. The area of descending solid and ascending partially molten material forms the asthenosphere and is ~100km thick. The supply of melt is fed by both mantle and lithosphere material. Initial results suggest that convection in the asthenosphere is necessary for melt to travel horizontally along the base of the lithosphere to heat pipe locations. In the absence of the convective motion, even in the presence of a slope near an existing heat pipe, the melt will excessively accumulate and not be extracted. Over the course of the model, some preexisting heat pipes close due to cooling. The closed heat pipes leave behind a conical elevation at the base of the lithosphere where melt collects. Heat release due to crystallization and shear heating occurs and the heat pipe reopens at depth.