Volume Changes Attending Hydration of Quenched Magnesium Sulfate Brine: The Tectonics of Ganymede's Sulci

The phase behavior of magnesium sulfate water at elevated pressures may have important applications to the understanding of tectonic features on Ganymede. Fractional volume changes accompanying crystallization, melting, hydration, and dehydration of MgSO4-H2O mixtures observed in the laboratory are as large as the global expansion proposed to explain extension in the grooved terrain. Expansion attending phase changes in thick cryovolcanic deposits offers an alternative to global expansion as a cause of fracturing in Ganymede's sulci. We report phase and volume changes from three data runs on a sample of 35.76 percent MgSO4, equivalent to MgSO4-12H2O at pressures of 96, 110, and 250 MPa.