Tectonic pressurization of aquifers in the formation of Mangala and Athabasca Valles, Mars

[1] Mangala and Athabasca Valles are the type examples of a distinct class of outflow channels that debouch directly from extensional tectonic features. We here demonstrate that the tectonic events responsible for the formation of the graben and fissures at the sources of the channels would have likely resulted in a near-instantaneous pressurization of the surrounding aquifers. Subsequent drainage of the pressurized aquifers though the confining cryosphere to the surface along the tectonically generated faults and fissures would have produced the catastrophic floods responsible for forming the channels. The peak discharges and individual flood volumes would have been dependent upon the magnitude of the individual tectonic events at the source regions. We estimate that individual extensional tectonic events at the source regions of Mangala and Athabasca Valles would have resulted in flood volumes ranging from 3 to 300 km 3 and peak discharges ranging from 10(5) to 10(6) m(3) s(-1). Our models further show that the entire extensional tectonic history of Athabasca Valles would have resulted in a total cumulative flood volume of 200 - 14,000 km(3), whereas that at Mangala Valles would have resulted in a total flood volume of 3000 - 22,000 km(3), both consistent with inferred flood volumes based on the geomorphology. Athabasca Valles in particular is of interest as it is the youngest of the outflow channels, demonstrating that this mechanism has brought substantial volumes of water to the surface in the present epoch.