Constraints on the history of open‐basin lakes on Mars from the composition and timing of volcanic resurfacing

Abstract

Abundant evidence exists for valley network‐related fluvial activity near the Noachian‐Hesperian transition on Mars, and areally significant quantities of volcanic ridged plains were emplaced during this period as well. Thus, it is worthwhile to explore the hypothesis that lava‐water interaction occurred on the surface of Mars at this time. We analyzed the morphology, physical properties, composition, and surface ages of thirty open‐basin lakes (topographic lows with both an inlet valley and an outlet valley) that were also resurfaced by volcanic flows. Hyperspectral imaging data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité (OMEGA) instruments indicate that of the 30 basins, 12 exhibit the spectral properties of basaltic lithologies with diagnostic absorptions of olivine, high‐calcium pyroxene and low‐calcium pyroxene. An olivine/high‐calcium pyroxene mixture is the most commonly identified mineral assemblage, consistent with other Hesperian‐aged volcanic units. Therefore, our mineralogical results for over a third of the open‐basin lake floors analyzed support prior interpretations that the basins were resurfaced by volcanic flows. Supporting evidence for resurfacing by volcanic flows is also given by the observed morphology and physical properties (e.g., surface roughness, thermal inertia) of the resurfaced open‐basin lake floors. In these 30 examples, however, no evidence was found for lava‐water interaction. The ages of emplacement, derived through counts of superposed craters, of all 30 of the open‐basin lake volcanic resurfacing units show that resurfacing began in the Late Noachian, near the Noachian‐Hesperian boundary, was concentrated in the Hesperian, and continued into the Early Amazonian. The lack of geologic features indicative of lava‐water interaction suggests that the basins were likely to have been mostly devoid of water at the time of the latest phase of volcanic resurfacing. We conclude that there is no geologic evidence that suggests the fluvial activity associated with the studied paleolakes was coeval with the emplacement of the observed volcanic resurfacing units, several of which date to the Late Noachian‐Early Hesperian.