The chronology of ordinary chondrites by laser Ar-Ar and I-Xe

Details The chronology of ordinary chondrites by laser Ar-Ar and I-Xe The chronology of ordinary chondrites by laser Ar-Ar and I-Xe

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29s.439a&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 439-440

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4

Argon Isotopes, Chondrites, Chronology, Laser Applications, Meteoritic Composition, Chemical Composition, Degassing, Inclusions, Mineralogy, Petrography, Potassium, Radioactive Age Determination

Scientific paper

We have separated a suite of chondrules, exotic clasts, and matrices from ordinary chondrites for the extraction of gases by laser ablation and stepped heating for Ar-Ar and I-Xe dating. A portion of each separated phase was also used for petrographic and mineralogical analysis. The age determined for a large equilibrated H chondrite clast from Barwell was found to be indistinguishable from the age of whole-rock samples of Barwell. The laser extraction method produces ages in good agreement with conventional extraction methods. Four samples from Parnallee have been analyzed and show a range of ages indicative of a highly complex chronology. The whole-rock stepped heating analysis for Parnallee shows that it is a highly disturbed system, but the variable Ar-Ar ages obtained for the inclusions indicate that this is not only due to the partial resetting of the Ar by a shock event about 1.9 Ga, but is also due to the different ages and age structures of the constituent components. The ages obtained by laser extraction for inclusions from other meteorites ranged from 0.9 b.y. to 3.6 b.y., with one exception. An age of 4.63 (+/- 0.04) b.y. was obtained for a large clast, from Quenggouk, containing mosaicized olivine and blebs of Fe-Ni metal that may have been subject high shock. This can lead to anomalously high ages as shown previously. It is hoped that I-Xe dating of this inclusion will help to show the causes of this anomalously high age and the degassing history of this inclusion. It is hoped that the complexities of the ordinary chondrite thermal histories will be clarified by the application of these high-sensitivity techniques to individual component parts of these meteorites.

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