Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.592w&link_type=abstract
Meteoritics, vol. 30, no. 5, page 592
Other
5
Chondrites, Cm, H, Ordinary, Interplanetary Dust Particles, Micrometeorites
Scientific paper
Interplanetary dust and meteorites are widely believed to originate predominantly from the asteroid belt [e.g., 1,2]. However, these two types of matter, which represent distinct mass classes (~10 micrograms and ~100 kg, respectively) seem to sample different reservoirs, as they are dominated by different types of extraterrestrial matter. The dust is mostly related to the CM-type chondrites [3], which are rare among meteorites that are otherwise dominated by ordinary chondrites (OCs) [2]. To quantify the contribution to the interplanetary dust by OC parent bodies we have studied 427 particles from the 100 - 400 micrometer size fraction of dust recovered from Antarctic ice [4], 303 of which were found to be of extraterrestrial origin. Of these, 41 (=13.5%) are cosmic spherules (CSs), 136 (= 44.9 %) scoriaceous micrometeorites (MMs), 65 (= 21.5%) consist of dehydrated phyllosilicates, 11 (=3.6 %) consist mainly of phyllosilicates, and 50 (= 16.5%) are coarse-grained crystalline MMs. Phase compositions of the crystalline MMs suggest a close relationship between these MMs and CM-type carbonaceous chondrites [e.g., 3]. Low-Ca pyroxenes and olivines are rich in Mg, Cr, and Mn, typical for carbonaceous chondrite phases [e.g., 5]. Only three crystalline MMs (~1% of the total extraterrestrial particle population) have phase compositions that are compatible with derivation from an OC precursor: Particle M6 (~200 micrometer diameter) has a porphyritic texture with olivine (Fa 18.7) and low-Ca pyroxene (Fs 16.6, Wo 0.6) in a fine-grained matrix. Micrometeorite AM1 (410 micrometers long) has also a porphyritic texture with olivines (Fa 16.2) set in a fine- grained, clinopyroxene-bearing matrix. Particle Mc7/10 (150 micrometers long) has a granular mosaic texture of intergrown olivine (Fa 17.6-19.8) and low-Ca pyroxene (Fs 14.1-16.3, Wo~1.2), and plagioclase (An 14), with very little intergranular matrix. Minor element contents of olivines in all three particles are low (CaO < 0.05 wt%, Al2O3 < 0.05 wt%, TiO2 < 0.05 wt%, Cr2O3 < 0.05 wt%, NiO < 0.02 wt%). The FeO/MnO ratios in olivine vary between 33 and 49, comparable to those of H-chondrite olivines [e.g., 6]. Two of the three particles were also analyzed by INAA [3]. Their trace element abundances match those of ordinary chondrites [e.g., 7]. We conclude that the three particles M6, AM1, and MC7/10 are related to H-chondrites and, thus, are likely to represent an asteroidal belt contribution to the interplanetary dust population. The abundance of OC-like dust is very low (1%), and up to now limited to H-chondritic particles - two equilibrated and one unequilibrated one. Acknowledgement: This work was supported by FWF (project P10688-GEO). References: [1] Brownlee D. E. (1981) in Comets and the Origin of Life (C. Ponnamperuma, ed.), 63-70. [2] Dodd R. T. (1981) Meteorites. [3] Kurat G. et al. (1994) GCA, 58, 3879-3904. [4] Maurette M. et al. (1991) Nature, 351, 44-47. [5] Steele I. M. (1986) GCA, 50, 1379-1395. [6] Brandstatter et al. (1985) Ann. Naturhist. Mus. Wien, 87A, 11-20. [7] Wasson J. T. and Kallemeyn G. W. (1988) Philos. Trans. R. Soc. Lond., A325, 535-544.
Brandstatter Frans
Koeberl Christian
Kurat Gero
Maurette Michel
Walter Jürgen
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