A new hematite formation mechanism for Mars

Abstract

Abstract-The origin of hematite detected in Martian surface materials is commonly attributed to weathering processes or aqueous precipitation. Here, we present a new hematite formation mechanism that requires neither water nor weathering. Glass-rich basalts with Martian meteorite-like chemistry (high FeO, low Al 2 O 3 ) oxidized at high (700 and 900 °C) temperatures in air and CO 2 , respectively, form thin (<1 µm) hematite coatings on their outermost surfaces. Hematite is manifested macroscopically by development of magnetism and a gray, metallic sheen on the glass surface and microscopically by Fe enrichment at the glass surface observed in element maps. Visible and nearinfrared, thermal infrared, and Raman spectroscopy confirm that the Fe enrichment at the oxidized glass surfaces corresponds to hematite mineralization. Hematite formation on basaltic glass is enabled by a mechanism that induces migration of Fe 2+ to the surface of an oxidizing glass and subsequent oxidation to form hematite. A natural example of the hematite formation mechanism is provided by a Hawaiian basalt hosting a gray, metallic sheen that corresponds to a thin hematite coating. Hematite coating development on the Hawaiian basalt demonstrates that Martian meteorite-like FeO contents are not required for hematite coating formation on basalt glass and that such coatings form during initial extrusion of the glassy basalt flows. If gray hematite originating as coatings on glassy basalt flows is an important source of Martian hematite, which is feasible given the predominance of igneous features on Mars, then the requirement of water as an agent of hematite formation is eliminated.

Martian surface mineralogy from Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité on board the Mars Express spacecraft (OMEGA/MEx): Global mineral maps

“…Several hypotheses have been presented to explain the apparent andesitic character of the Acidalia‐type spectrum: weathering of basalt to produce clay minerals [ Wyatt and McSween , 2002], silica coating basalt [ Kraft et al , 2003], water‐bearing minerals such as opaline, silica‐rich allophane like mineraloids, and the most silica‐rich zeolites [ Michalski et al , 2005], oxidation and recrystallisation of a SNC‐type basalt [ Minitti et al , 2002], palagonization of basalt [ Morris et al , 2003], oxidation at high temperature of a glass‐rich basalt flows [ Minitti et al , 2005]. These proposed mineralogies and implied origins offer broad possibilities for processes of formation.…”

“…At shorter wavelengths, the brighter coating is optically thick keeping albedo high, while at longer wavelength it becomes increasingly transparent so that the basaltic substrate becomes spectrally dominant. If surfaces of dark material are moderately weathered in the form of a thin varnish of ferric oxide‐bearing rinds, this would produce this “blue” NIR continuum slope without water band at 1.9 μ m. Another very interesting process that produces an anhydrous, ferric coating over a glass‐rich basaltic substrate consists in an oxidation of a basaltic substrate at high temperatures (700° and 900°C) in air and CO 2 [ Minitti et al , 2005]. This process can be also considered as possible.…”

Redox kinetics of iron in alkali silicate glasses exposed to ionizing beams: Examples with the electron microprobe

“…The atomic oxygens accumulated at the glass surface makes two neighboring Fe 2+ to precipitate as Fe 2 O 3 oxide clusters in a more polymerized glass network (four NBOs have been replaced by two BO). Hematite phases (α-Fe 2 O 3 ) were shown to have precipitated at the surface of basaltic glasses exposed to oxidizing conditions [40]. Fig.…”

Detection of Biosignatures by Geomatrix-Assisted Laser Desorption/Ionization (GALDI) Mass Spectrometry

“…Recent results from Martian rover missions showed the presence of small, spheres of hematite, so-called "blueberries," which provide evidence of past existence of water on Mars (Minitti, et al 2005). Both evaporate deposits and evaporite minerals are targets for Martian exploration because the former form in the presence of standing water and the latter form wherever dissolved salts remain after desiccation (Schaeffer 1990;WynnWilliams and Edwards 2000;Ellery and Wynn-Williams 2003).…”