Spectral and petrologic analyses of basaltic sands in Ka'u Desert (Hawaii) – implications for the dark dunes on Mars

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Dark aeolian deposits on Mars are thought to consist of volcanic materials due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated. Basaltic dunes on Earth are promising analogs for providing further insights into the assumed basaltic sand dunes on Mars. In our study we characterize basaltic dunes from the Ka'u Desert in Hawaii using optical microscopes, electron microprobe, and spectral analyses. We compare the spectra of terrestrial and Martian dune sands to determine possible origins of the Martian dark sediments. Our results show that the terrestrial sands consist primarily of medium to coarse sand-sized volcanic glass and rock fragments as well as olivine, pyroxene, and plagioclase minerals. Grain shapes range from angular to subrounded. The sample composition indicates that the material was derived from phreatomagmatic eruptions partially with additional proportions of rock fragments from local lava flows. Grain shape and size indicate the materials were transported by aeolian processes rather than by fluvial processes. Spectral analyses reveal an initial hydration of all terrestrial samples. A spectral mineralogical correlation between the terrestrial and Martian aeolian sands shows a similarity consistent with an origin from volcanic ash and lava. We suggest that the Martian deposits may contain similar abundances of volcanic glass, which has not yet been distinguished in Martian spectral data.

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