Aqueous Processes From Diverse Hydrous Minerals in the Vicinity of Amazonian-Aged Lyot Crater

Lu Pan (1, 2) , Bethany Ehlmann (1)

1 CALTECH - California Institute of Technology
2 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement

Amazonian-aged Lyot crater is the best-preserved and deepest peak-ring impact crater (diameter, D = 220 km) in the northern lowlands of Mars. Morphological features including scouring channels emanating from its ejecta and small channels within the crater have been examined previously to understand hydrological activity associated with the crater. In this study, we analyze images acquired by the Compact Reconnaissance Imaging Spectrometer for Mars on board the Mars Reconnaissance Orbiter to investigate the mineralogical record in Lyot and its surroundings, which are presently enriched in ground ice, to understand the associated aqueous processes, their relative timing, and a possible role for ground ice in hydrous mineral formation. We find diverse hydrous minerals, including Fe/Mg phyllosilicates, chlorite, illite/muscovite, and prehnite in Lyot crater walls, central peak, and ejecta, as well as in two craters to the west of Lyot. The exposure and distribution of the hydrous minerals suggest that they are related to the impact process, either exposed by the excavation of hydrothermally altered rocks or formed through syn-depositional hydrothermal alteration immediately after impacts. The Lyot impact induced channel formation to the north, but no mineralogical evidence of aqueous alteration associated with the channels is observed. The sinuous channels within Lyot, diverted by bedrock units with hydrous mineral detections, did not cause mineralization but likely represent the last stage of water activity in Lyot crater. The separate episodes of water activity indicate flow of liquid water on Mars' surface during the Amazonian but limited to no aqueous alteration to generate hydrous minerals. Plain Language Summary Though liquid water is not stable on the surface of Mars presently, water may have had a more active role on Mars in the recent geologic epoch. In particular, meteor impacts may melt ground ice, creating local environments with liquid water activity. Lyot crater is the deepest, well-preserved impact crater in the northern plains of Mars, with a diameter of 220 km, formed in the most recent geologic epoch. In this work, we study the mineralogy and morphology related to water activities within and adjacent to Lyot crater. One of the mineral types (prehnite) found in Lyot form at relatively high temperature (>200°C) in hydrothermal environments. From the distribution of water-bearing minerals, we found that they probably represent an earlier episode of water activity before or during the impact. While liquid water has carved small channels inside the crater long after the impact, they probably did not exist on the surface long enough to alter the composition of the bedrock materials. Liquid water may be present but probably quite short-lived in the most recent epoch on Mars.

Domaines: Planète et Univers [physics]; Sciences de la Terre; Planétologie

Lu Pan, Bethany Ehlmann. Aqueous Processes From Diverse Hydrous Minerals in the Vicinity of Amazonian-Aged Lyot Crater. Journal of Geophysical Research. Planets, 2018, 123 (7), pp.1618-1648. ⟨10.1029/2017JE005461⟩. ⟨hal-02283960⟩