Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.320b&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 320
Other
3
Micrometeorites
Scientific paper
Previously, [1] studied the bulk chemistry and texture of 223 micrometeorites from Greenland (size: 100-200 micrometers): 82% spherical, 6% porous, and 12% monomineralic particles or particles with unique textures and from Antarctica (size: 50-100 micrometers): 24% spheres, 62% porous, and 14% particles with unique textures. In order to obtain information about the origin of micrometeorites we have studied minerals within these particles that escaped melting during atmospheric heating. Relict olivine grains occur in 27 spheres, 3 porous particles, and 11 particles with unique textures. Relict olivines (mostly > 5 micrometers in apparent size) can be distinguished from secondary crystallized (subsequent to atmospheric melting) olivines by their grain size, morphology, composition, and/or the presence of Fe/Ni-metal inclusions in olivine. Previously, [2] studied 26 Mg-rich olivines from Antarctic micrometeorites and [3] investigated about 70 olivines in micrometeorites from Antarctica and Greenland. Within the 41 micrometeorites containing such grains, 98 relict olivines were analyzed by electron microprobe, representing a much wider range of compositions than reported by [2]. In most micrometeorites, only one or two relict olivines occur and were large enough to be analyzed. In some particles, however the Fa-contents of several relict olivines were obtained (Fig. 1). Relict olivines with Fa-contents below 5.2 mol% Fe are abundant (Fig. 1). One forsterite within a porous particle is manganese- enriched and similar in composition to LIME olivines known from IDPs and primitive meteorites [4]. Comparing olivines from chondrites with those in micrometeorites, Fa-poor olivines occur in Type I chondrules from carbonaceous chondrites [5] and as isolated olivines in the matrix of C2, C3, and unequilibrated ordinary chondrites [2]. Between Fa(sub)5.2 and Fa(sub)~12 a gap exists in the distribution of the Fa-contents (Fig. 1). Relict olivines, however, with about 12 and 30 mol% Fa occur. These Fa- contents are similar to those of equilibrated H, L, and LL chondrites and may indicate that many particles are related to ordinary chondrites. In addition, several other micrometeorites contain olivines with Fa-contents exceeding those of olivines in ordinary chondrites. Considering chondrites as potential material of their origin, they may be related to matrix olivines in Type III carbonaceous chondrites and to olivines in Type II chondrules [5]. In six micrometeorites relict olivines with highly variable compositions were analyzed, indicating that the precursor was unequilibrated prior to thermal processing during atmospheric entry. Comparing all data, it appears that the larger-sized particles from Greenland may contain a slightly higher abundance of forsteritic relict olivines than the small particles from Antarctica. However, we cannot rule out that this observation is a result of insufficient data. References: [1] Beckerling W. et al. (1992) Meteoritics, 27, 200- 201. [2] Steele I. M. (1992) GCA, 56, 2923-2929. [3] Christophe Michel-Levy M. and Bourot-Denise M.(1992) Meteoritics, 27, 73-80. [4] Klock W. et al. (1989) Nature, 339, 126-128. [5] McSween H. Y. (1977) GCA, 41, 477-491.
Beckerling W.
Bischoff Addi
Klöck W.
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