Mössbauer Spectroscopy of Mineral Separates from Snc Meteorites

Introduction: Numerous workers have recently focused attention on the issue of the oxygen fugacity (fO2) of martian samples [1,2,3,4,5]. Estimates of fO2 based on Fe-Ti oxides [6] and DEu/DGd and DEu/DSm ratios [3,4,7] suggest a range of fO2 values for SNC meteorites from IW+2.5 IW+3.5 for Shergotty to IW2.0 IW+0.2 for QUE94201 [3,4]. Fe/Fe is also a function of fO2, and synchrotron micro-XANES values for olivine, pyroxene, and feldspar Fe have been reported in [8,9]. However, the relationship between the reported Fe values and the other methods for estimating fO2 is not clear, and further measurements of Fe/Fe by a more conventional technique have been needed. Accordingly, in this project, new Mössbauer spectroscopy data on mineral separates handpicked from 10 SNC meteorites are reported. Previous Work: Previous work on these meteorites is summarized in Table 1. The only workers to extract and analyze mineral separates were Ostertag et al. (olivine) [20, 21], Vieira et al. [22], and Vistisen [23] (pyroxene), and these data show only very small percentages of Fe in olivine and pyroxene. However, none of the previous workers has related the Fe/ΣFe of the bulk separates to the Fe contents and modes of individual minerals present, so Fe/ΣFe ratios of individual phases could not be assessed. Table 1. Mössbauer Spectroscopy of SNC Samples Meteorite Analysis %Fe ALHA 77005 WR [10, 11, 14] 1.7-1.8 olivine separate [20, 21] 4.5 Chassigny WR [12, 13, 14] 2.3 EETA 79001 WR [10, 14, 15] 0.5-1.9 Governador Valadares WR [14, 15] n.s.