EVIDENCE FOR PERSISTENT AND CATASTROPHIC FAULT-CONTROLLED FLUID FLOW ON MARS

High fracture density locally develops in relay between fault segments potentially providing vertically extensive regions of high permeability facilitating focused pathways for groundwater to flow to the surface environment of Mars. On Earth such pathways are exploited by groundwater flow localized along faults over a variety of time-scales from smaller, persistent flow to larger, catastrophic events. Persistent flow is often localized within the damaged rock associated with the fault; episodic events are associated with stress perturbations resulting from earthquakes or magmatic injection and include both localized outflow along fault traces, e.g., sand boils, in a process sometimes referred to as seismic pumping, as well as regional changes in water table. Both phenomena are documented in the modern record through changes in spring flow, water level in monitoring wells, or direct exploitation in geothermal and petroleum systems as well as the geologic record where they are interpreted from bleaching/alteration of rock adjacent to fractures, vein formation, and implosion breccia. On Mars, persistent, non-catastrophic fluid flow is also observed, both as groundwater flow resulting in bleaching in regions of relay faulting in Candor Chasma and possible fluid flow at fault tips and intersections in the Nili Fossae region. Several large outflow channels, such as Athabasca and Mangala Valles, originate at fault relays and may have formed by tectonic pressurization and seismic pumping. These catastrophic outflows are associated with relays that in terrestrial systems are shown to produce dilation resulting in high fracture density that is associated with concentrated hydrothermal outflow. Therefore, future studies of possible hydrothermal activity on Mars should consider regions of complex fault geometry.