Alteration processes in volcanic soils and identification of exobiologically important weathering products on Mars using remote sensing

Abstract

Abstract. Determining the mineralogy of the Martian surface material provides information about the past and present environments on Mars which are an integral aspect of whether or not Mars was suitable for the origin of life. Mineral identification on Mars will most likely be achieved through visible-infrared remote sensing in combination with other analyses on landed missions. Therefore, understanding the visible and infrared spectral properties of terrestrial samples formed via processes similar to those thought to have occurred on Mars is essential to this effort and will facilitate site selection for future exobiology missions to Mars. Visible to infrared reflectance spectra are presented here for the fine-grained fractions of altered tephra/lava from the Haleakala summit basin on Maui, the Tarawera volcanic complex on the northern island of New Zealand, and the Greek Santorini island group. These samples exhibit a range of chemical and mineralogical compositions, where the primary minerals typically include plagioclase, pyroxene, hematite, and magnetite. The kind and abundance of weathering products varied substantially for these three sites due, in part, to the climate and weathering environment. The moist environments at Santorini and Tarawera are more consistent with postulated past environments on Mars, while the dry climate at the top of Haleakala is more consistent with the current Martian environment. Weathering of these tephra is evaluated by assessing changes in the leachable and immobile elements, and through detection of phyllosilicates and iron oxide/oxyhydroxide minerals. Identifying regions on Mars where phyllosilicates and many kinds of iron oxides/oxyhydroxides are present would imply the presence of water during alteration of the surface material. Tephra samples altered in the vicinity of cinder cones and steam vents contain higher abundances of phyllosilicates, iron oxides, and sulfates and may be interesting sites for exobiology.

Spectral identification of hydrated sulfates on Mars and comparison with acidic environments on Earth

“…These gossans include poorly-crystalline or nanophase iron oxide and silicate phases as well as jarosite. Morris et al (1996Morris et al ( , 2000 and Bishop et al (1998a) have found jarosite, alunite, alunogen and other sulfate species in a range of volcanic tephra and ash samples formed through hydrothermal alteration. Such Fe-and Al-bearing sulfates also may have formed on Mars through similar processes.…”

Characterization of waste rock associated with acid drainage at the Penn Mine, California, by ground-based visible to short-wave infrared reflectance spectroscopy assisted by digital mapping

“…As the identification method is geared to comparison after continuum removal of absorption features, spectra with extremely weak features were taken to represent unidentifiable Fe minerals or poorly crystallized Fe substances if no match was found. Identification of poorly crystallized nanocrystalline (grain size b9 Am) Fe 3+ minerals, which may be common as pigmentary agents in rocks in the waste piles, is difficult because of the lack of knowledge of their spectral features in natural mixtures, such as those containing well-crystallized Fe minerals (Morris et al, 1993;Bishop et al, 1998). Sulfides, the ultimate target of most aciddrainage remediation, generally can be readily identified in the field through visual examination.…”

A new hematite formation mechanism for Mars

“…One example of such a process is palagonitization of basaltic glass (Morris et al , 1993(Morris et al , 2000, which can yield both nanophase (amorphous) and fine-grained (crystalline) red hematite. In addition to palagonitic alteration, pedogenic and solfataric alteration of basaltic glasses are all capable of producing nanophase and/or fine-grained red hematite (e.g., Bishop et al 1998Bishop et al , 2002Bishop et al , 2004Morris et al , 1993Morris et al , 2000Schiffman et al 2000Schiffman et al , 2002. The preferred formation mechanism proposed by Christensen et al (2000) for the coarse, gray hematite is precipitation from Fe-rich water (at ambient or hydrothermal temperatures).…”