Hydrogen Isotope Measurements of Gypsum and Jarosite in Martian Meteorite Roberts Massif 04262: Antarctic and Houstonian Weathering

Introduction: The secondary minerals of Martian meteorites have long fascinated the scientific community due to their possible formation on Mars, which in turn can provide insight into weathering processes on Mars. Minerals such as jarosite have a restricted set of formation conditions and can provide information as to the pH, Eh, latitude and temperature of fluids on Earth [1-4]. Ca-sulfate (gypsum and/or bassanite) was first described in basaltic shergottite EETA 79001 [5]. Ca-sulfate, Ca-carbonate and Mg-phosphate salts in vugs show evidence of Martian origin from carbon isotopes of carbonate [6]. Jarosite has been recently described in the nakhlite MIL 03346 and has a Martian !D [7]. The findings of jarosite by MER at Meridiani Planum [8] and gypsum (and possibly bassanite) in Valles Marineris by the ESA MEX OMEGA [9] demonstrate the importance of these minerals as weathering products on the Martian surface. Terrestrial formation of these low-temperature alteration products is can provide valuable information, as constraints can be provided into how Martian basalts weather, although under different conditions. While jarosite and gypsum/bassanite have been described from different classes of Martian meteorites, in the Roberts Massif 04262 shergottite, both minerals have been putatively identified [10]. Mineralogy and geochemisty of jarosite and gypsum analyzed here was described in [10]. Briefly, Fe-sulfide (pyrrhotite) and apatite show evidence of significant low-temperature alteration relative to that previously described in other shergottites and nakhlites [1,7,10]. A hydrous iron-phosphate is also associated with the jarosite minerali-zation. Here we report hydrogen isotope measurements of gypsum and jarosite in RBT 04262 in order to determine the last location of hydrogen isotope equili-bration. Methods: The Cameca ims 1270 ion microscope with SCAPS 2-D ion imaging detector at Hokkaido University (Hokudai) was used to determine the spatial variability and ratios of hydrogen and deuterium in gypsum and jarosite mineralization in RBT 04262,40. More detailed methodology can be found in [10], albeit modified for different mineralogy. Terrestrial jarosite and gypsum were used to correct for instrumental mass fractionation.