Other
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27..291s&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 291
Other
3
Scientific paper
Antarctic micrometeorites (AMMs) show resemblances and differences to both stratospheric interplanetary dust particles (IDPs) and chondritic meteorites, but the exact nature of this relationship has yet to be established. We measured Ne, H, C, and N isotopic compositions, as well as trace element abundances in several AMMs in order to compare the results to similar measurements of IDPs (Stadermann, 1991). AMMs for this study were collected near Cap-Prudhomme (Maurette et al., 1989), and optically selected (Olinger et al., 1990). Noble gases of 23 selected AMMs were extracted through laser vaporization. Nine of these particles contained implanted solar Ne and one showed a clear signature from spallogenic Ne, confirming their extraterrestrial origin. We selected fragments from 6 of these particles, plus 2 containing apparent Ne excess and one with a roughly chondritic bulk chemistry but immeasurably low Ne, for further analyses. Secondary ion mass spectrometry (SIMS) was used to measure the H, C, and N isotopic compositions. These measurements turned out to be difficult, since the concentrations of H and C in the analyzed samples were significantly lower than in IDPs. The low concentration of C also affected the N isotopic measurements because N could only be measured as CN-. We were able to measure H in 9, as well as C and N in 3 AMMs. All measurements yielded isotopically normal results. Previous determinations of the O isotopic compositions of the same samples (Virag, pers. comm.) also gave no indication of isotopic anomalies. These results are significantly different from measurements of IDPs, where isotopic anomalies in H and N were found in roughly 1/2 and 1/3 of the particles, respectively. SIMS was also used to measure the rare earth and trace element abundances in up to 4 different fragments of 6 AMMs. Although most particles had roughly chondritic abundances, anomalous concentrations were found for Ca, Li, Co, Ni, and Ba. Significant Ca depletions up to 0.03 x C1 were observed in 5 out of 6 particles. This effect is well known from IDPs but nonetheless little understood. Enrichments up to 10 x C1 in Li and up to 100 x C1 in Ba were detected in 4 particles each. The Ba enrichment in AMMs has been observed before and can most likely be attributed to terrestrial contamination (Maurette et al., 1992). The origin of the unusual Li enrichment is unknown. Ni was depleted in all analyzed particles and was strongly correlated with Co, whose depletions relative to C1 were always smaller than for Ni. In the particle with the largest Ni-Co depletion, a melted sphere, this effect was accompanied by an Fe depletion. The Fe/Si, Co/Si and Ni/Si ratios relative to C1 were (0.4, 0.06, 0.02). Similar correlated depletions of Fe, Co, and Ni were also found in 2 out of 13 IDPs with otherwise chondritic abundances (Stadermann, 1991). The ratios of their Fe, Co, Ni depletions were (0.2, 0.07, 0.01) and (0.3, 0.03, 0.01), respectively. Interestingly, these 2 IDPs also contained H with isotopically normal composition and C concentrations that were too low for C and N isotopic measurements. One of these particles was a melted spherule. All these similarities suggest that some AMMs and some IDPs may have close relationships, although AMMs and IDPs in general do not represent the same class of extraterrestrial material. Maurette M. et al. (1989) Lunar Planet. Sci. 20, 644-645. Maurette M. et al. (1992) Lunar Planet. Sci. 23, 859-860. Olinger C.T. et al. (1990) Earth Planet. Sci. Lett. 100, 77-93. Stadermann F.J. (1991) Lunar Planet. Sci. 22, 1311-1312.
Olinger Chad T.
Stadermann Frank J.
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