Conspicuous assemblages of hydrated minerals from the H2O-MgSO4-CO2 system on Jupiter's Europa satellite

Water ice, hydrated salts, and other volatile ices such as carbon dioxide (CO2), have been detected by spectroscopy on Europa's surface. Although the presence of other candidate compounds like clathrate hydrates have not yet been observed on the moon, the existence of water and carbon dioxide combined with low temperature and relatively high cryostatic pressure in the interior of the planetary body, favors their occurrence. In this study, the evolution of the H2O-MgSO4-CO2 system as a function of temperature, pressure and high salt concentration was investigated, focusing especially on the differences between the resulting mineral parageneses. CO2-clathrate formation and dissociation were examined by Raman spectroscopy in the presence of other hydrated phases crystallized from aqueous solutions rich in magnesium sulfate (MgSO4) at several concentrations (5, 17 and 30 wt%) from 268 to 290 K and pressures up to 60 bar. The CO2-clathrate experimental equilibrium line in this salty system is presented for both gas and liquid CO2 stability fields. During the heating process, the mineral assemblage of the system evolved differently depending on the salt concentration. At subsaturation (5 wt% of MgSO4), the CO2-clathrate co-existed with water ice from 268 to 272 K. However, when the initial sulfate concentration was 17 wt%, at a temperature above 269 K, no mineral phase was stable apart from CO2-clathrate. If the salt concentration of the system was supersaturated (30 wt%), CO2-clathrate co-existed with meriadianiite (MgSO4·11H2O) from 269 to 275 K. Subsequently, meridianiite was transformed into epsomite (MgSO4·7H2O) and continued crystallizing until 300 K. The evolution of the supersaturated solution at different heating rates was also evaluated in detail. In experiments with the fastest heating, the epsomite was not stabilized and the resulting aqueous solution became more concentrated than initially, promoting a clathrate dissociation at lower temperatures than expected. Volume changes due to mineral transformations and partial/total melting processes were assessed for the system and applied to Europa's geology. Thus, assuming that this system is present in Europa's interior, the evolution of the presumed fluids and mineral assemblages may have resulted in the generation of local stresses promoting resurfacing. Depending on the initial composition of the system, the percentage of volume change would imply a chaotic terrain formation, or cause faulting.