Jarosite, Hematite, and Smectite In the Aqueous Alteration Material of the Yamato-000593/794 Nakhlite (Martian Meteorite)

The MER landers on Mars provide evidence of widespread aqueous alteration by acid sulfate solutions. Alteration in the Martian meteorites, however, has been ascribed mostly to neutral solutions, based on the presence of carbonates and smectite clays (even though some of their smectite material is rich in sulfate and chloride; Treiman, 1983). Evidence that Martian meteorites experienced acid sulfate alteration has come only recently from several reports of jarosite in the nakhlite and chassignite meteorites (igneous rocks that crystallized at ~1.3 Ga, fairly young in Mars' history; Kuebler et al. 2003; Herd, 2006; Vicenzi et al., 2007).

The nakhlite meteorite Y-00593/794 (found in Antarctica) contains abundant aqueous alteration materials (Treiman & Goodrich, 2002; Noguchi et al., 2003) concentrated in and near olivine grains. Three textures are present. Space-fillings are regions filled with concentric, alternating layers of smectite (identified by EMP composition and shrinkage under vacuum) and jarosite + hematite (identified by EMP and Raman spectra; Noguchi et al., 2003). Anatase and akaganeite (?) are also present. Crack fillings are linear regions, apparently in and next to cracks, of material rich in jarosite (as in the MIL03346 nakhlite; Herd, 2006; Vicenzi et al., 2007). Crack-fillings cut both space-filling material and olivine grains. Between crack-fillings and unaltered olivine is brown material, which has Raman spectra like ‘iddingsite' alteration of terrestrial olivine (Kuebler et al., 2003).

These results suggest that the Y000593/794 was affected by oxidized acid sulfate solutions, which deposited jarosite, hematite, and smectites, and altered olivine to ‘iddingsite.' Several nakhlites also contain siderite, FeCO3 (Bridges & Grady, 1999; Treiman, 2005), which is unstable in the acidic oxidizing environment of jarosite deposition, and suggests multiple episodes of alteration or strongly evolving fluids. -2008-->