Physics
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..384l&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 384
Physics
Diffusion, Exposure Ages, H Chondrites, Weathering
Scientific paper
We present the distribution of the elements F, Cl, Br, and I in 14 different H5 and H6 chondrites from Allan Hills, Elephant Moraine, Lewis Cliff Ice Tongue, and Thiel Mountains. The depth distribution was measured in stepwise removed layers from the surface into the interior. The dimensions of the investigated pieces from the individual meteorites were about 2 x 2 x 2 cm. All meteorites show higher halogen concentrations on their surfaces than in the interior, especially for I (enrichment factor up to 850 in the first few millimeters). This contamination happens mainly when the meteorites are lying on the surface of the Antarctic ice [1]. A contamination during the time the meteorite resides enclosed in the ice is not very likely because the ice has low halogen concentrations [2] and the temperatures are always below the freezing point of water. The different halogen species deposited onto the surface of a meteorite may diffuse into the interior; this process can be enhanced by water. The degree of contamination with F, Cl, Br, and I increases linearly with time for a meteorite and can be correlated neither with its degree of weathering nor with its terrestrial age. The major contamination source for F, Cl, and probably Br is airborne sea spray. It seems to be the same for all meteorites (same ratio of enrichment). The major contamination source for I is the biogenically CH(sub)3I produced in the sea [3,4]. This molecule and its products of oxidation in the Antarctic atmosphere (e.g., I(sub)2) can be transported over longer distances to the inner regions of Antarctica than airborne sea spray (inorganic aerosols) [3,5]. H chondrites found toward the center of Antarctica (e.g., Lewis Cliff or Thiel Mountains) are therefore less contaminated relative to I by F, Cl, and Br than those found near the coast (e.g., Allan Hills or Elephant Moraine). References: [1] Langenauer M. and Krahenbuhl U. (1993) Meteoritics, 28, 98- 104. [2] Legrand M. R. and Delmas R. J. (1985) Ann. Glaciol., 7, 20-25. [3] Heumann K. G. et al. (1987) GCA, 51, 2541-2547. [4] Heumann K. G. et al. (1990) GCA, 54, 2503-2506. [5] Legrand M. R. and Delmas R. J. (1988) JGR, 93D, 7153-7168. Fig. 1, which appears here in the hard copy, shows a map of Antarctica showing the four places from which H5 and H6 chondrites were studied. Numbers in parentheses give the quantity of analyzed meteorites.
Krähenbühl Urs
Langenauer Marcel
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