Evidence of Mafic Volcanic Compositions Associated with Domes in Arcadia

Introduction: Domes and more oblong and irregularly shaped mounds have been described from the Arcadia and Utopia Planitiae regions on Mars [1,2,3]. In [1] it was suggested that the domes in Arcadia were volcanic domes and they were compared to terrestrial volcanic domes with silica contents generally higher than have been associated with known volcanic products on Mars. In [2] it was posited that these domes, and similar features just to the west of Utopia Planitia, might be more comparable to tephra mounds similar to those formed by sub-ice volcanism on Earth. In [3] these domes were compared to relatively rare basaltic volcanic domes. Here we analyze spectral evidence from the CRISM, THEMIS, and TES sensors to examine possible mineral spectroscopic evidence that could illuminate the nature of these features. Locations and Description of Domes: The domes in Arcadia Planitia mostly lie between 34 and 46˚N latitude and 167 to 180˚E longitude, and those in western Utopia Planitia primarily between 38 and 45°N and 76 to 86°E. As described in [1], these domes and more irregularly shaped hills consist of features with a central mound, an apron, and often an irregularly toned aureole surrounding the apron. Their heights average around 160 m with diameters averaging around 1.5 km. Some domes, described in [1] as " blisters " , lack the apron and aureole and appear to be upraised plains material. Data: THEMIS data were examined as decorrela-tion stretch (DCS) composites (radiance and emissivi-ty). CRISM FRT scenes have been collected over several of these domes. CRISM data were converted to apparent surface reflectance using a " volcano scan " approach [4]. Currently we are also working on utilizing a look-up table correction from DISORT radiative transfer modeling [5]. Multi-and Hyperspectral Analysis: THEMIS multispectral daytime IR data indicate differences in the spectra of domes and aprons compared to the background plains; these features can also display differences among each other (Fig. 1). In Fig. 1, the dome marked " 1 " appears yellow in the band 8,7,5 DCS composite while that marked " 2 " appears purple. Domes that appear yellow in the 8,7,5 combination appear yellow green in a band 9,6,4 combination and red to magenta in a band 6,4,2 DCS combination. CRISM FRT's 8EE5, 9700, and 9A7D (the latter two being a paired observation) cover domes in the