FUMAROLE ALTERATION OF HAWAIIAN BASALTS: POTENTIAL MARS ANALOG

Over the last decade of Mars exploration, planetary scientists have discovered abundant magnesium and iron sulfates, hematite, and silica, suggesting alteration of basalts in water-limited, saline-acidic conditions, consistent with acidic evaporates or potentially sulfur-rich fumaroles (Morris et al, 2000; Squyres and Knoll, 2005; Bibring et al., 2006). In order to understand the formation of the minerals observed on Mars, it is necessary to understand the geochemical and mineralogical pathways basalt undergoes when it weathers under different conditions. This will lead to a better understanding of the water-limited, acid-sulfate weathering history of Mars, in particular the sulfate-bearing Gusev Crater soils and bedrock where sulfur-rich hydrothermal processes are believed to have been involved (Squyres et al., 2007) and Meridiani Planum deposits, where acid-sulfate evaporitic conditions are generally preferred (Squyres et al., 2009).

Kilauea volcano, Hawaii currently has active fumaroles in contact with basalts and previous studies have identified mineral assemblages similar to those found on Mars (Morris et al., 2000). Rock samples from young fresh and altered basalts from different fumarolic environments were collected in order to determine the mineral assemblages and element mobility patterns associated with this kind of alteration. The results will serve as a terrestrial analog to help determine the origin of the sulfur-rich deposits seen on Mars.

Rock and mineral samples were collected at and near the rim of Pu‘u ‘Ō‘ō, the drill hole at Sulfur Banks, Kilauea Iki, Mauna Ulu, and the Kalakai Caves. Fresh and altered lavas and the associated mineral coatings were collected near active fumaroles. Some of the samples were analyzed in the field with a TERRA portable X-ray Diffractometer (XRD) in order to identify any ephemeral minerals that might not survive transport. In the laboratory, the samples were analyzed by XRD and X-ray Fluorescence (XRF), providing the mineral assemblages and bulk chemical composition. Sulfates and phosphates were the most commonly detected alteration minerals. Halides, clays, and zeolites were also present. Several minerals were only seen in the freshest samples from Pu‘u ‘Ō‘ō indicating that there is a temporal element to the preservation of these minerals.