Sunday, January 10, 2016

Was the Noctis Labyrinthus on Mars Produced by Groundwater Flows Collapsing the Ground Above?

Groundwater flow induced collapse and flooding in Noctis Labyrinthus, Mars


Rodriguez et al


Catastrophic floods of enormous proportions are thought to have played a major role in the excavation of some of the Solar System’s largest channels; the circum-Chryse outflow channels. The generation of the floods has been attributed to both the evacuation of regional highland aquifers and ancient paleo-lakes. Numerous investigators indicate that these source regions were likely recharged and pressurized by eastward groundwater flow via conduits extending thousands of kilometers from an elevated groundwater table in the Tharsis volcanic rise. This hypothesis remains controversial, largely because subsequent stages of Valles Marineris development and enlargement would have resulted in the widespread destruction of the proposed groundwater paths. Here, we show that Noctis Labyrinthus, a unique canyon system connecting the Tharsis volcanic rise and western Valles Marineris, retains geologic evidence of conduit development associated with structurally-controlled groundwater flow through salt-rich upper crustal deposits, consistent with aquifer drainage from the Tharsis volcanic rise region. Our investigation indicates that subsequent surface collapse over these conduits during the Hesperian Period resulted in the generation of large basins in the central and eastern regions of Noctis Labyrinthus, and contributed to the chasmata formation in the western portion of Valles Marineris. The lava-covered floors of these basins, dated by previous workers as Late Amazonian, contain hydrated mineral deposits occurring in spatial coexistence with decameter-scale features that we interpret to be lacustrine and periglacial in origin. The proposed paleo-lake sites also include chaotic terrains, which could comprise groundwater discharge zones, pointing to regional hydrologic processes that could have operated from the Early Hesperian until a few tens of millions of years ago. Episodic fluidized discharges from eastern Noctis Labyrinthus troughs delivered vast volumes of sediments and volatiles into western Valles Marineris, contributing to the construction of a regional volatile-rich stratigraphy. Episodic groundwater discharges and the resulting intermittent formation of lakes within regional tectono-volcanic basins could have lasted hundreds of millions of years, making the study region of prime interest for astrobiological exploration.

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