Hydrated silica in alluvial fans and deltas on Mars

International audienceRecent studies that suggest transient, intense surface runoff on Mars in the last 3 billion years are at odds with thecanonical views of the early transition of Mars surface environments from wet to dry. The abundant hydrous minerals on the Martian surface are key to unraveling the surface environment and water chemistry in Mars’ history. Silica-rich materials have been expected on Mars due to silica liberation during basalt weathering [1] and later identifiedusing orbital data [e.g. 2-5] as well as in situ [6-8]. Here we present the analysis of silica deposits in multiple alluvial fans and deltas on Mars, combining the mineral detections with inferred surface runoff of alluvial/fluvial deposits. Multiple silica deposits associated with fans and deltas have been analyzed using hyperspectral data acquired from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and digital elevation models (DEM) computed from overlapping Mars high-resolution image datasets. We find silica concentrated in layered exposures in the terminal deposit of relatively short channels and small fans with no obvious source deposits. Combined with hydrological analysis of the local surface runoff environments, we aim to better constrain the water chemistry and temperature during the era of fan/delta formation, which likely corresponds to the latest episode of hydrous mineral formation on Mars.[1] McLennan (2003) Geology, 31(4), 315–318. [2] Milliken et al. (2008). Geology, 36(11), 847–850. [3] Skok et al.(2010). Nature Geoscience, 3(12), 838–841. [4] Carter (2011). Thesis Université Paris Sud - Paris XI. [5] Sun & Milliken (2018). Geophys. Res. Lett., 44, 4716–4724. [6] Squyres et al. (2008) Science 320, 1063. [7] Ruff et al. (2011). J. Geophys. Res. 116, E00F23. [8] Rapin et al. (2018). J. Geophys. Res. Planets. 123, 1955-1972