Barriers to Melt Ascent in the Lithosphere of Io With Applications to Heat Pipe Formation

Abstract

Melt from the presumed magma ocean in Io's interior reaches the surface at well‐documented paterae and hotspots. To do so, melt needs to cross the thermal lithosphere of Io, even though, as it loses heat, it may stall inside the lithosphere. Permeability barriers form when melt crystallization is rapid and further prevents melt ascent unless a different melt transport mechanism develops. The heat pipe model of Io provides such a mechanism, allowing the melt to travel from the molten asthenosphere to the surface at discrete points. However, unless these heat pipes are billions of years old and constant in both location and flux, melt must ascend through the cold lithosphere at other locations and form new melt conduits. We model here the crystallization sequence of melts as they rise through the lithosphere of Io and determine under what conditions a permeability barrier may form. The barrier is generally deep, but can be elevated 100s of meters to several kilometers in areas of high strain rate or low resurfacing rate. We propose a feedback mechanism where regions closer to a heat pipe experience a higher resurfacing rate, driving the permeability barrier deeper, while regions away from a heat pipe experience a lower resurfacing rate allowing the permeability barrier to rise. A new heat pipe may develop in these regions where the melt is focused by variations of permeability barrier elevation while the old heat pipe closes, potentially leading to changes of heat pipe location over a time scale of 100,000 years.