Hydrothermal Alteration Products of Basaltic Material on Mauna Kea as a Template for Detection of Hydrothermal Alteration on Mars

Phyllosilicate-poor palagonitic tephra is a well-recognized spectral and magnetic analogue for Martian bright regions, and palagonitization has been postulated to be an important surface weathering process on Mars based on comparisons of palagonite composition and mineralogy to previous telescopic and spacecraft measurements of Mars. Formation of poorly ordered palagonitic tephra from glassy basaltic materials on the Earth implies alteration at non-hydrothermal temperatures. However, well-crystalline hydrothermal alteration minerals are often found in close association with poorly ordered phases like palagonites in regions where the geologic environment changes dramatically over short distances. One such region is Mauna Kea volcano (Hawaii), where a combination of shield and littoral volcanism, pyroclastic eruptions (some possibly subglacial), and subaerial weathering processes have all acted to modify the precursor basaltic materials within relatively recent geologic time. We are investigating the mineralogical and chemical composition of hydrothermal alteration products of basaltic material on Mauna Kea as a guide to specific hydrothermal alteration products that might be present on Mars. Using a combination of techniques including spectroscopy (reflectance, Mossbauer), analytic chemistry, and magnetic properties studies, we have identified kaolinite, smectite, jarosite, and alunite as hydrothermal alteration products in the specific regions that we have sampled. By understanding the remote sensing signatures of these hydrothermal alteration products in the presence of other altered and/or unaltered materials, these kinds of analogue studies can enhance the ability to detect these kinds of minerals in currently available data (e.g., Hubble Space Telescope images and spectra and Mars Global Surveyor TES spectra) and future data sets from the Mars Odyssey orbiter THEMIS instrument and the Mars Exploration Rover Athena instrument suite. Based on our experience with the scale and diversity of mineralogies and weathering environments on Mauna Kea and other terrestrial analog locations, the much higher spatial resolution of these new Mars data sets could dramatically improve the detectability of localized hydrothermal deposits.