Other
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27r.296t&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 296
Other
4
Scientific paper
Hydrated interplanetary dust particles (IDPs) may comprise up to 50% of all collected IDPs [Schramm et al., 1990]. However, controversies still exist regarding their formation, history, and relationship to other primitive solar system materials [e.g., Germani et al., 1990; Thomas et al., 1990]. We have examined six hydrated IDPs and determined their mineralogy and bulk chemical compositions, including carbon abundances, using electron microscopy [procedures described in Thomas et al., 1992a]. Our initial examination of these hydrated IDPs showed that some particles were also enriched in carbon up to ~6 x CI [Thomas et al., 1992b]. Element abundances and carbon ratios to bulk Orgueil are given in Table 1. For all 6 IDPs, element abundances ratioed to Orgueil are within a factor of two of CI for most elements; a regular exception is C, which ranges from ~2.5-6.3 x CI. Four of the particles have been described previously [Thomas et al., 1992b]. Two additional IDPs (L2006G1 and L2006J14) contain phyllosilicates with basal spacings of 1.0 nm, but no anhydrous silicates were observed. L2006G1 contains abundant Fe-sulfides and is the only particle analyzed that contains distinct Mg-Fe carbonate grains. L2006J14 contains abundant Fe-sulfides and has a discontinuous magnetite rim up to ~50 nm thick indicative of atmospheric entry heating [Thomas et al., 1992b]. Our results indicate that all of the analyzed hydrated IDPs have significantly higher carbon abundances than the most carbon-rich carbonaceous chondrites. The range of carbon abundances in hydrated IDPs overlaps that of anhydrous IDPs (~0.5-7 x CI) [Thomas et al., 1992a]. Carbon in anhydrous IDPs occurs as regions of spongy-textured, poorly crystalline material acting as a matrix holding individual mineral grains together [Thomas et al., 1992a] Carbonaceous material may be distributed in hydrated IDPs in a similar manner but is difficult to differentiate from fine-grained, poorly crystalline phyllosilicate matrix. Fine-grained carbonates could account for some but not all of the high carbon abundances in hydrated IDPs. Hydrated IDPs are generally believed to be derived from asteroidal sources that have undergone some degree of aqueous alteration [e.g., Thomas et al., 1991]. However, our data indicate that some hydrated IDPs are markedly enriched in C relative to CI chondrites. The only known chondritic material with similar levels of C are some anhydrous IDPs that are probably derived from comets [Thomas et al., 1992a]. Therefore, we propose that hydrated IDPs with high C abundances (>3 x CI) are derived from cometary bodies rather than hydrous asteroids. REFERENCES: Anders E. and Grevesse N. (1989) GCA 53, 197. Germani M.S. et al. (1990) LPSC 21, 415. Thomas K.L. et al. (1990) LPSC 21, 1250. Thomas K.L. et al. (1991) LPSC 22, 1395. Thomas K.L. et al. (1992a) GCA (in review). Thomas K.L. et al. (1992b) LPSC 23,1427. Schramm L.S. et al. (1990) Meteoritics 24, 99. TABLE 1. Carbon abundances (wt%) ratioed to bulk carbon in Orgueil, element abundances including carbon (in wt%) for six hydrated IDPs, and literature values for Orgueil [Anders and Grevesse, 1989]. Relative errors for major and minor elements are within 5%, while the relative errors for carbon are within 20%. Sample IDP C/ C Na Mg Al Si S Ca Fe Ni Orgueil C L2006G1 5.7 20 1.5 9.6 0.8 13.0 4.0 0.7 11.7 0.8 L2006J14 6.3 22 1.4 12.0 1.1 13.0 1.6 0.2 9.9 0.6 L2005R7 2.6 9 0.9 11.8 1.4 19.3 2.9 0.1 18.9 0.8 L2005P9 5.7 20 0.8 8.0 1.3 10.3 2.1 0.1 27.7 0.7 L2005L6 3.4 12 0.8 10.2 0.9 12.1 3.1 1.4 27.1 2.7 L2005P13 3.1 11 0.5 11.4 1.0 14.0 3.2 2.4 25.4 0.7 Orgueil 3.5 0.5 9.5 0.9 10.7 5.3 0.9 18.5 1.1
Blanford George E.
Keller Lindsay P.
McKay David S.
Thomas Kathie L.
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