Ancient groundwater flow in the Valles Marineris on Mars inferred from fault trace ridges

Abstract

Groundwater is a crucial reservoir in Mars's global water cycle and plays an important role in aqueous alteration of bedrock. Understanding groundwater flow is also important for assessing the possibility of past and present martian life. The Valles Marineris is a series of fault-bounded troughs and chasms stretching over 4,000km from west to east, with a width of 600km and depth of up to 10km below the surrounding high plains. In this region, ancient groundwater movement is suggested by links between chasms of the Valles Marineris and the sources of catastrophic floods in chaotic collapse terrains. Here, images obtained by the Viking, Mars Express, Mars Reconnaissance Orbiter and Mars Odyssey missions are used to map ridges on the walls of the Valles Marineris that extend in an east-west direction up to the surface of the surrounding high plains from almost 7km beneath. These erosion-resistant ridges, which can be tens of kilometres long, most likely represent cementation of the fault zones and surrounding rock by water-deposited minerals and suggest that groundwater in this region flowed for long distances through major east-west-trending fault systems. This interpretation implies that liquid water was stable at (or near) Mars's surface when the fault zones were cemented ~3,500-1,800Myr ago and that chemical deposition from groundwater was regionally significant.