Other
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.529s&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 529-529
Other
Chondrites, Deserts, Meteoritic Composition, Rare Gases, Weathering, Adsorption, Degassing, Dissolving, Radioactive Isotopes
Scientific paper
Many new meteorites have been recovered from hot desert regions during recent years. These generally heavily weathered chondrites have terrestrial ages up to a few 104 yr, which are younger than those of the less-weathered Antarctic meteorites. We have investigated the influence of weathering on the noble gas record. Concentration and isotopic composition of all noble gases were measured in 30 ordinary chondrites from hot deserts, mainly from the Sahara, the Nullabor Plain, Roosevelt County, and Chile. The results are compared with those of Modern Falls and Antarctic finds respectively. Most of the hot desert chondrite samples contain elevated concentrations of trapped Ar, Kr, and Xe in spite of a preheating at 140 C in-vacuo for 48 hr. Since the isotopic composition of Xe suggests an atmospheric origin, it is concluded that the high concentrations of Kr are also due to a terrestrial contamination. High concentrations of Kr are correlated with low Xe-132/Kr-84 ratios. Finds with high Kr concentrations have ratios of about 0.2, which is higher than the atmospheric value of about 0.04. This implies an elemental fractionation during the trapping process. Stepwise heating experiments show that for strongly weathered meteorites most of the atmospheric Kr is lost after degassing the chondrite for 30 min at 800 C. The treatment of weathered meteorites with acids removes weathering products but does not completely remove the atmospheric gases. Weathering products are not the only carrier of these gases. 'Irreversible adsorption' could be responsible for the incorporation of atmospheric noble gases into other meteoritic mineral grains.
Loeken Th.
Scherer Peter
Schultz Ludolf
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