Abstract

Mangala Valles has always been viewed as the typical outflow channel formed by catastrophic floods of water. A new analysis has shown that the geomorphological traces of fluvial or lacustrine processes within Mangala Valles can be better explained by fluid lava flooding the channels and filling pre-existing impact craters. As for the circum-Chryse outflow channels, where no clear source of water or mechanism able to replenish water at its hydraulic head-is observed, there is no geologic trace of a sudden removal of a volume of water (ice) necessary to carve Mangala Valles. Neither maars nor rootless cones, typical volcanic features indicative of interaction between lava and ground ice, were found. Past works suggested that the formation of Mangala Valles occurred in late Amazonian age when the climate of Mars was similar to that seen today, that is absolutely not liquid water friendly. The present work shows how the origin of Mangala Valles may go back to Noachian or even Pre-Noachian when other studies have concluded that the climate was not liquid water friendly. Even assuming limited periods of obliquity favourable to liquid water in the history of Mars, which is at odds with the widespread presence of unaltered olivine and jarosite, it is very difficult to find plausible mechanisms of aquifer recharge or signs of catastrophic water release at the Notch of Mangala Valles that could feed the multiple episodes, or even a single episode, of fluvial flooding suggested in the literature. This evidence and other analysis will show that the presence of water and, eventually, ground ice is not incontrovertible in the equatorial regions and should not be given for granted as commonly done so far in the literature. The geomorphological analysis of the Mars Reconnaissance Orbiter (MRO) images provided in this paper, combined with THEMIS and MOLA data, show how Mangala Fossa, from which Mangala Valles originated as a breakout, is an erosional channel formed by the flow of lava in a original tube coming from Daedalia Planum rather than a tectonic graben or the sign of a dike rupturing to the surface. (C) 2017 Elsevier B.V. All rights reserved.