Chapter 4 - Dry megafloods on Mars: formation of the outflow channels by voluminous effusions of low viscosity lava

Abstract

Listen

Translate article

The outflow channels of Mars are enormous channel systems that show evidence for having developed as a result of voluminous effusions of fluids from the subsurface. These systems remain widely interpreted as products of sudden discharges of groundwater from enormous aquifers, and such interpretations have led to inferences that otherwise unexpectedly large subsurface reservoirs of water exist on Mars, and that relatively warm and wet conditions have intermittently prevailed at the surface. However, the basic properties of the outflow channels are not suggestive of aqueous origins. Obvious sedimentary deposits of fluvial or diluvial origin, and the extensive swaths of hydrated minerals expected of channel reaches incised into geological units that hosted groundwater over geological timescales, are yet to be identified at the outflow channels. The pervasive hydrous alteration and thick evaporite units expected of terminal basins are also yet to be found. Plausible mechanisms by which aquifers might have catastrophically released groundwater to the surface remain elusive. Instead, the outflow channels have properties aligned with those of ancient volcanic systems that formed by voluminous eruptions of low-viscosity lavas on bodies including the Moon, Mercury, Venus, and Earth. In contrast with hypothesized aqueous origins, dry volcanic origins are consistent with the lithological and geochemical properties of materials preserved along the Martian outflow systems. The high-rate effusion of low-viscosity lavas on Mars would have been a natural consequence of the pressures generated within ancient igneous plumbing systems that extended into mantle source regions. Dry volcanic origins for the Martian outflow channels have considerable potential to reverse many of the inferences previously made on the basis of aqueous channel interpretations, transforming our view of the history and basic properties of Mars.