Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.486k&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 486
Computer Science
3
Achondrites, Antarctic Regions, Chondrites, Halogens, Meteoritic Composition, Weathering, Enrichment, Geochronology, Ion Selective Electrodes, Neutron Activation Analysis
Scientific paper
Antarctic chondrites show a pronounced enrichment of halogens on their surface. The extended investigation of the alteration and depth profiles of the concentrations of F, Cl, Br, and I has revealed their relation to the duration of the exposure to the Antarctic atmosphere and the changes of the I/F ratio as a function of the collection site (distance to the open sea). The weathering index deduced from visual inspection of the collected specimen and of a thin section thereof is not related to the measured enrichment of halogens in Antarctic chondrites. After the investigation of a large number of H5 and H6 chondrites from different locations within Antarctica, the goal of this study was to do a similar examination on achondrites. The samples investigated were a eucrite from the Allan Hills, ALH 81011, and a second eucrite from the Nullarbor Plains in Western Australia, Camel Donga. The concentrations of the stepwise, mechanically removed layers were obtained by neutron activation technique and in the case of F by ion selective electrodes after pyrohydrolytic decomposition of the samples. The results of the two eucrites are given. For both achondrites the contamination in halogens from the surface only reaches to a shallow depth of about 1 mm. The enrichment factors (surface over volume) of the four investigated elements are less pronounced than in chondrites. The terrestrial age of the ALH 81011 is not known. Under the assumption of a similar contamination as for chondrites in Antarctica, the surface exposure age is probably on the order of 2000 yr.
Krähenbühl Urs
Langenauer Marcel
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