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Ferric iron in SNC meteorites as determined by Mössbauer spectroscopy: Implications for martian landers and martian oxygen fugacity
Author(s) -
DYAR M. Darby
Publication year - 2003
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2003.tb00012.x
Subject(s) - mineral redox buffer , meteorite , martian , olivine , pyroxene , astrobiology , fugacity , nontronite , mössbauer spectroscopy , mineral , chondrite , chemistry , mars exploration program , analytical chemistry (journal) , mineralogy , geology , oxygen , physics , crystallography , environmental chemistry , clay minerals , organic chemistry
— Mössbauer spectra of martian meteorites are currently of great interest due to the Mössbauer spectrometers on the Athena mission MER rovers as well as the European Space Agency Mars Express mission, with its Beagle 2 payload. Also, considerable current effort is being made to understand the oxygen fugacity of martian magmas because of the effect of f O 2 on mineral chemistry and crystallization processes. For these 2 reasons, the present study was conceived to acquire room temperature Mössbauer spectra of mineral separates and whole rock samples of 10 SNC meteorites. The results suggest that mineral identification using remote application of this technique will be most useful when the phases present have distinctive parameters arising from Fe in very different coordination polyhedra; for example, pyroxene coexisting with olivine can be discriminated easily, but opx versus cpx cannot. The MER goal of using Mössbauer spectroscopy to quantify the relative amounts of individual mineral species present will be difficult to satisfy if silicates are present because the lack of constraints on wt% FeO contents of individual silicate phases present will make modal calculations impossible. The remote Mössbauer spectroscopy will be most advantageous if the rocks analyzed are predominantly oxides with known stoichiometries, though these phases are not present in the SNCs. As for the detection of martian oxygen fugacity, no evidence exists in the SNC samples studied of a relationship between Fe 3+ content and f O 2 as calculated by independent methods. Possibly, all of the Fe 3+ observed in olivine is the result of dehydrogenation rather than oxidation, and this process may also be the source of all the Fe 3+ observed in pyroxene. The observed Fe 3+ in pyroxene also likely records an equilibrium between pyroxene and melt at such low f O 2 that little or no Fe 3+ would be expected.