Groundwater filling times for large impact basins on early Mars and implications for the onset of post impact hydrothermal systems

Post impact hydrothermal (PIH) systems may provide conditions suitable for the origin and evolution of life. Constraining the duration of these systems is of great interest and is the target of many terrestrial studies. Some of the better studied craters, such as the Chicxulub and Chesapeake Bay impact structures, formed in a shallow marine setting where the resurgence of seawater may have initiated PIH activity. In contrast, the largest impacts on Mars, such as Hellas and Argyre basins, formed on the martian highlands where sea water incursion was not possible, and the lack of quenching may have extended the longevity of PIH systems.

In this study, we investigate the timescales required to fill large impacts via groundwater flow. We focus on groundwater because no literature exists on the subject, martian paleo-precipitation is poorly constrained, and groundwater flow could be substantial in the early Mars environment. We hypothesize that this was a protracted process and gradual seepage into hot impact basins would slow the onset of PIH activity. It may also provide the wetting-drying cycles thought to be essential for pre-biotic chemistry.

We conducted a combination of laboratory experiments and numerical simulations with the basic question: how does the filling of the lake reduce the groundwater inflow by continuously raising the base level? We performed experiments in bead packs draining into closed reservoirs, and scaling analysis shows that the dynamics solely depend on the ratio between the crater lake and pore volumes. We conducted complementary numerical simulations with both the Dupuit approximation and full two-phase flow equations. After validating the simulations against experiments, the results are extrapolated to larger impact basins on Mars to provide first-order estimates on potential filling times and onset of PIH activity. These estimates have possible implications for the duration of thermophilically suitable conditions within these basins.