STRONG LITHOSPHERIC RESISTANCE LIMITS POTENTIAL FOR EUROPAN SEAFLOOR VOLCANISM (Invited Presentation)

In a sunless Europan ocean, a hypothetical biosphere cannot be sustained by photosynthetic processes. Instead, it must rely on consistent geochemical input from Europa’s ice shell and mantle. One such possible input is the generation of reactants through hydrothermal activity, serpentinization, and other byproducts of volcanic processes occurring on or just below Europa’s seafloor. However, silicate melting is thought to occur at depth in Europa’s mantle (> 100 km) and therefore any magma produced must penetrate and travel through a thick, resistant lithosphere in order to erupt. We conceptualize this process as occurring via the initiation and propagation of large, lithospheric-scale magmatic dikes due to melt pooling at the base of the Europan silicate lithosphere. In order to determine if mantle magmatic processes are sufficient to overcome Europa’s lithospheric resistance, we constructed a model of Europa’s mantle in the simulation code StagYY with a new melt extraction routine. In order to erupt, modeled mantle melt must be sufficiently buoyant to overcome the lithosphere’s tensile strength, forming a dike. This dike must then propagate upwards at a sufficient rate to reach the surface before cooling and solidifying as heat conducts into the cooler surrounding rock.

Preliminary results suggest that the potential for Europan seafloor volcanism is strongly limited by this lithospheric resistance. We find that, under present conditions, Europan mantle melt is unable to fracture rocks with tensile strengths greater than 2 MPa, comparable to the tensile strength of terrestrial rock at 20 km depth and plausibly Europa’s lithosphere. When a dike is initiated, we find that magma is unable to penetrate more than a few meters into the lithosphere. For our considered reference model conditions, average dike influx was 1x10^-4 m²/s, leading an average propagation height of 0.5 m and a maximum height of 1.7 m. We find that dike influxes on the order of 1 m²/s (equivalent to large terrestrial fissure eruptions) are generally required for eruption. Work is ongoing to characterize the influence of various mantle parameters (such as permeability, heat production, and magma viscosity) on eruptability to determine if those theoretical influxes are possible.