Surficial Geology of Siloe Patera at Arabia Terra, Mars

Abstract: Siloe Patera, like other collapsed volcanic features at Arabia Terra, Mars has been identified as a set of nested deep depressions [1]. We interpreted surficial geology, including possible geologic history, of Siloe Patera by combining analysis of spectral analysis from TIR data of THEMIS, mineralogic phases (e.g. olivine, phyllosilicate, and hydrated silicates) from NIR data of CRISM, and local morphology from HiRISE and CTX. We identified four spectral units: the purple, fuchsia/magenta, yellow/amber, and pale-brown or green (typical terrain) unit. Purple unit, which occurs on eastern and north-eastern scarps, has weighted absorption center (WAC) [2] in longer wavelengths (consistent to lower silica content), and has higher thermal inertia (indicating bedrock materials) and the presence of olivine. Like the purple unit, the fuchsia unit confirms the presence of rich olivine phase. Yellow unit, near the central peak, home to elevated silica content, includes a transverse dune field on the edge of the peak, and is composed of coarse-grained dune sands, and weak phyllosilicate abundance. Typical terrain (pale brown or green) unit is the most dispersed unit and has elevated silica content; it consists of fine grain dust showing positive abortion to the phyllosilicate index, and in some areas shows hydrated phyllosilicate phase spatially adjacent to the network of channels and gullies. We suggest that the presence of faulting consistent with collapsed features and related lava-flow features confirm that Siloe Patera is a collapsed caldera of Late Noachian to Early Hesperian [1], which was modified by subsequent water-related processes. References: [1] Michalski, J.R., Bleacher, J.E., 2013. Supervolcanoes within an ancient volcanic province in Arabia Terra, Mars. Nature 502, 47–52. [2] Amador, E.S., Bandfield, J.L., 2016. Elevated bulk-silica exposures and evidence for multiple aqueous alteration episodes in Nili Fossae, Mars. Icarus 276, 39–51.