Depth‐profiles and surface enrichment of the halogens in four Antarctic H5 chondrites and in two non‐Antarctic chondrites

Abstract

Abstract-Depth-profiles of F, C1, Br and I concentrations were determined in four different Antarctic H5 chondrites from the Allan Hills and in the two chondrites Allende (C3) and Holbrook (L6). Pieces of the meteorites were studied by analysis of stepwise removed layers of 0.5-1.0 mm thickness up to a depth of 9 mm. Neutron activation analysis and ion-selective potentiometry were used for the determination of C1, Br, I and for F, respectively. The Antarctic meteorites show higher concentrations of the halogens at the surface compared to the interior. The highest enrichment factors are found for I and CI and the lowest for Br. In contrast, F shows the steepest concentration gradient and is only enriched in the first 2.5 mm below the surface. The other halogens have penetrated deeper into the meteorites. The measured enrichments at the surfaces are not correlated to the visible degree of weathering. The analysed non-Antarctic meteorites, which were recovered shortly after their observed fall, demonstrate similar halogen concentrations at the surface, including the fusion crust, as in the interior. Based on these results we present a model to estimate the degree of contamination and the relation to the duration of exposure at the surface of the Antarctic ice.

Iodine monoxide in the Antarctic snowpack

“…Rock samples showed a decrease of the iodine -but not bromine and chlorine -concentration from the surface to the centre of the samples, leading to the conclusion that atmospheric iodine compounds react with surfaces of Antarctic rocks. This finding was confirmed by halogen depth profiles in Antarctic chondrides, which showed an enrichment in iodine at the surface not present in samples anywhere else in the world (Langenauer and Krähenbühl, 1993). Heumann et al (1987) found an iodine enrichment not only on meteorites, but also in Antarctic snow samples.…”

Comparative Study of Activation Analyses for the Determination of Trace Halogens in Geological and Cosmochemical Samples

“…In fact, no iodine content was obtained for JG-1, for which RNAA yielded a value with a large uncertainty due to poor counting statistics. For Allende, our RNAA and RPAA values for I are consistent with each other and also with literature data 2,5,14,15 except one value. 17 It is noted that some variation in I values may stem from the heterogeneous distribution of iodine in meteorite samples.…”

“…As seen in Table 7, our RNAA data for Allende and geological reference rocks are reasonably consistent with literature values. [13][14][15][16] Although RPAA has nominally comparable sensitivity to that of RNAA as shown in Table 4, no data could be reliably obtained for geological standard rocks by RPAA, being consistent with detection limit values listed in Table 5. Iodine.…”

“…For Allende, all our values are consistent with each other and also with one literature value. 13 Two other literature values 14,15 (237 and 228 μg/g) seem to be systematically lower than the other values including ours. For JB-1 and JG-1, our data are all consistent with their literature values.…”

“…When one determines fluorine in Allende, corrections for the side reaction from sodium became significant, reaching to 50 to 60%. Our value is among the range of literature values, [13][14][15] which have large scatterings from 25 to 55 μg/g. Our fluorine value for JG-1 (475 ± 39 μg/g) is in excellent agreement with a literature value 16 (498 μg/g).…”