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The interior structures of planetary bodies beyond the Earth are broadly unknown. Our observational capacity is largely limited to surface imagery from spacecraft. The work presented in this dissertation uses novel modeling methods of melt migration and melt focusing processes to illuminate the thermal and structural characteristics of the lithospheres of Mars and Jupiter’s moon Io. Models are constrained by, and inform observations of, surface volcanism.

Coupled petrological-geodynamical models of one-dimensional melt migration are performed to determine the depth of impermeable boundaries, known as permeability barriers, in the lithosphere of Mars. Relatively deep permeability barriers are found to be prevalent throughout Martian history unless in regions of high strain rate (10^-13 s^-1), or a wet mantle (25-1000 ppm H2O). Permeability barrier depth is suggested to be linked to the style of volcanic edifice seen at the surface, with deep barriers creating larger edifices like shield volcanoes, and shallower barriers creating widespread flows.

Similar petrological-geodynamical models performed for the lithosphere of Io reveal that permeability barriers always form at the base of the lithosphere due to the cold temperatures caused by geologically rapid resurfacing (~1 cm/yr) and subsidence. Melt may ascend closer to the surface in areas with a low subsidence rate (0.02 cm/yr)

Two-dimensional numerical models of melt migration in the Martian lithosphere suggest that convection in a highly porous layer beneath a permeability layer (a decompaction channel) focuses melt over the convective wavelength. Melt ascends in the lithosphere at this wavelength which is reflective of volcano spacing at the surface for Hesperian aged terrains.

Numerical and analytical models of melt flow through the asthenosphere and lithosphere of Io constrain the lifespan of its volcanic plumbing systems. A 1 km conduit will fully close within ~10,000 years while a 25 km conduit of melt will close within 6-7 million years. Solid convection in the asthenosphere is found to be necessary for melt focusing to heat pipe centers at the base of the lithosphere, however it is counterintuitively found that an arrangement with downwelling undeath the eruptive center is the most efficient for melt extraction.