Distribution of halogens in an Antarctic ordinary chondrite, Y-74014 (H6)

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One of the striking features in Antarctic meteorites is overabundances of halogens, especially iodine. In order to investigate how these halogens are distributed in constituent mineral phases of Antarctic chondrites, the outer portion of Yamato (Y)-74014 H6 chondrite (Y-74014,101) was subjected to fractional dissolution using several solutions with different chemical properties. Pulverized meteorite sample was successively leached by acetone, (hot) water, EDTA and nitric acid, and individual leachates as well as the acid residue were analyzed for halogens by neutron activation analysis. About 10% of iodine was recovered in acetone whereas only less than 2% of Cl and Br are leached, suggesting that overabundant iodine is partly present in the form of acetone-soluble, possibly organic compound. Dissolution patterns of Cl and I with water are similar to each other. This implies that contaminated Cl and I both reside in a common phase, presumably in akaganeite, a corrosion product of Fe-Ni alloy with chlorine attracted from the environment. Either iodine was involved in this mineral when corrosion reaction occurred or iodine was later migrated into the mineral by exchanging with Cl^- and/or OH^-. For the chronological studies using long-lived nuclides such as ^<36>Cl and ^<129>I, it is essential to use indigenous halogens in meteorites. For such purposes, the acid-residual fraction can be used even for Antarctic meteorites having overabundant halogens. In addition, Cl, Br and I contents in bulk Allende and Bruderheim chondrites are also obtained in this study and their abundances are briefly discussed.
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Distribution of halogens in an Antarctic ordinary chondrite, Y-74014 (H6)

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