Mathematics – Logic
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.546m&link_type=abstract
Meteoritics, vol. 30, no. 5, page 546
Mathematics
Logic
18
Anomalies, Isotopic, Compounds, Organic, Interplanetary Dust Particles, Reflectance, Spectral
Scientific paper
Previous studies have shown that a large fraction (~1/3) of collected interplanetary dust particles (IDPs) have substantial enrichments in D, of up to ~2,500 per mil [1]. Additionally, measurements often show large variations in the D/H between the subfragments of a given IDP. These large D enrichments and isotopic heterogeneity indicate the primitive nature of the material. We report here the results of isotopic measurements of five fragments from a large 'cluster' IDP (L2005 #31), together with chemical and mineralogical studies of these and six other fragments from this cluster. Three of the fragments (3, F1, and 4) are extremely enriched in D with values of 8,000, 20,000, and 24,800 per mil respectively. These are the largest D excesses ever observed in a natural sample, in the laboratory. The two remaining fragments (A2A and A2B), are only modestly enriched in D (~600 per mil), indicating that the carrier of the D enrichment is heterogeneously distributed throughout the cluster. Ion imaging of fragment 4 shows that the D is concentrated relative to the H, though the concentration is not as extreme as previously observed in the IDP Butterfly [2]. Fragments 3 and 4 were also found to have 15N excesses of ~260 per mil. Heavy N has been previously observed in IDPs [3], and is usually associated with D enrichments (although the reverse is not necessarily true). C isotopic measurements of fragments 3 and 4 were normal within uncertainty. Microprobe two-step laser mass spectrometry (micrometerL^2MS) was used to investigate fragments F1, A2A and A2B for the presence of polycyclic aromatic hydrocarbons (PAHs). Previous work [4] has shown that some IDPs contain rich distributions of organics. Analysis of fragment F1 revealed a suite of simple unalkylated and alkylated PAHs closely resembling those observed on carbonaceous chondrites. Neither of the fragments A2A or A2B had PAHs above the sub-attomole detection limit. Consistent with previous results, PAHs have only been observed in D-rich IDPs, although the reverse is not true. Bulk compositions (including C and O) for all eleven fragments were measured using SEM/EDX techniques [5], and subsequently analyzed using reflectance spectroscopy. Six of the fragments were prepared for ultramicrotomy using two techniques: three fragments were embedded in epoxy, and the remaining three will be embedded in sulfur. The three fragments in epoxy have been sectioned and examined in the TEM. All eleven fragments have chondritic abundances of most major and minor elements, although carbon is present at 2 to 3x CI levels. The reflectance spectra fall into two groups: 8 fragments have spectra that are flat or rise into the red, while 3 fragments show a pronounced drop-off into the near IR. The three very D-rich fragments have the reflectance characteristics of the first group. Fragment A2B falls into the second group, while A2A appears to be a mixture of both. TEM data indicate that the fragments in the first group are anhydrous, while the latter are hydrated. The anhydrous fragments are dominated by enstatite, with lesser Fe-Ni sulfides, carbonaceous material and GEMS (glass with embedded metal and sulfides), and traces of magnetite and chromite. Enstatite grains contain solar flare tracks with a density of ~1 to 5x10^10 cm^-2. The hydrated fragment contained major saponite, Fe-Ni sulfides, along with carbonaceous material, and traces of chromite, magnetite and enstatite. We are currently pursuing correlated TEM and Ion Probe investigations of fragments from this cluster. References: [1] McKeegan K. D. et al. (1985) GCA, 49, 1971-1987. [2] McKeegan K. D. et al. (1987) LPS XVIII, 627-628. [3] Stadermann F. J. et al. (1989) Meteoritics, 24, 327. [4] Clemett S. J. et al. (1993) Science, 262, 721. [5] Thomas K. L. et al. (1993) GCA, 57, 1551.
Chillier Xavier D. F.
Clemett Simon J.
Keller Lindsay P.
Messenger Scott
Thomas Kathie L.
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