The Volatile Content of Anhydrous Interplanetary Dust

Details The Volatile Content of Anhydrous Interplanetary Dust The Volatile Content of Anhydrous Interplanetary Dust

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.349f&link_type=abstract

Meteoritics, vol. 28, no. 3, volume 28, page 349

Mathematics

Logic

11

Carbonaceous Chondrites, Ci Chondrites, Interplanetary Dust Particles, Volatile Elements

Scientific paper

Flynn and Sutton [1] reported differences in the volatile contents of normal-Ca and low-Ca IDPs suggesting the anhydrous IDPs are more volatile rich than either the hydrated IDPs or the CI carbonaceous chondrites [1]. We tested this on 14 anhydrous, chondritic IDPs identified by Analytical Transmission Electron Microscopy. Trace element abundances were determined by Synchrotron X-Ray Fluorescence. The Fe-normalized average trace element content of the 14 anhydrous IDPs is higher than CI for the volatiles Cu, Zn, Ga, Ge, Se, and Br by factors ranging from 3 to 31. Five anhydrous IDPs show no evidence of heated textures or magnetite rims. These 5 Type-1 IDPs [2] all contain unequilibrated olivines, indicating that since their formation, they have not been heated sufficiently to equilibrate. Each volatile trace element is enriched above CI in every one of these 5 IDPs, except Ge = .9xCI in one, and Zn = .66xCI and .36XCI in two. The average volatile content is enriched to 1.4 to 47 times CI. Eight anhydrous IDPs show mineralogical evidence of atmospheric entry heating (eg., magnetite rims), and generally have a narrower range of olivine compositions. Their average volatile content is also greater than CI for all elements except Zn, but the pattern is different. There is a large Zn depletion, previously linked with entry heating [3], and Ge and Br are also depleted by factors of 3 or more compared to the 5 unequilibrated, anhydrous IDPs. One anhydrous IDP, L2005C19, has atypical contents of Zn (41xCI) and Cu (10xCI), which could indicate that it is not genetically related to the other anhydrous IDPs or that the parent body has inhomogeneous distributions of Zn and Cu on the 10-micrometer scale. L2005C19 contains Fe-Zn-sulfide, but only a minor amount of fine-grained aggregates, which make up more than 80% of the 5 unequilibrated IDPs. Although L2005C19 has a 100 nm thick magnetite rim, the high He^4 content and low release temperature of another cluster fragment suggest low heating [5]. The 5 unequilibrated anhydrous IDPs have significantly higher contents of the volatiles Cu, Zn, Ga, Ge, Se, and Br than do the CI chondrites. These IDPs are mineralogically distinct from anhydrous carbonaceous chondrites in that the olivines generally have low Fe-content (Fa 1 to 25). The unequilibrated olivines indicate that these anhydrous IDPs have not experienced the thermal event that partially equilibrated olivines even in CV3 matrix from meteorites like Allende have, nor have these IDPs experienced the aqueous alteration that affects the hydrated CI meteorites. Thus these unequilibrated, anhydrous IDPs are likely to better preserve the record of early solar system processes than do most meteorites. References: [1] Flynn G. J. and Sutton S. R. (1992) Meteoritics, 27, 220-221. [2] Klock W. et al. (1990) LPS XXI, 637-638. [3] Flynn G. J. et al. (1993) LPS XXIV, 495-496. [4] Flynn G. J. et al. (1992) LPS XXIII, 375-376. [5] Nier A. O. and Schlutter D. J. (1992) Meteoritics, 27, 166-173. Fig. 1, which appears here in the hard copy, shows CI and Fe normalized trace element contents of 14 anhydrous IDPs, 5 unequilibrated, anhydrous IDPs, and 8 heated, anhydrous IDPs. One anhydrous IDP, L2005C19, is not included in either subgroup because of its atypical chemistry and mineralogy and ambiguous heating history. The vertical lines show the range of abundances measured in the 5 unequilibrated, anhydrous IDPs.

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