Gas retention chronology of Petersburg and other meteorites

Details Gas retention chronology of Petersburg and other meteorites Gas retention chronology of Petersburg and other meteorites

Jul 1972

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1972gecoa..36..755p&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 36, Issue 7, pp.755-772

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21

Scientific paper

Argon and xenon data are presented for a thermal release study on a neutron-irradiated sample of the eucrite meteorite Petersburg. Xenon spallation corrections are made by the method of correlation systematics, and the relationship of lunar systematics to the systematics derived for the Angra dos Reis meteorite is discussed. Correlation systematics are also used in reevaluation of neutron-activation xenon data for other meteorites in which spallation effects are prominent. Petersburg has no excess Xe 129 attributable to in situ decay of I 129 , and a Pu 244 / U 238 ratio corresponding to onset of xenon retention 146 ± 14 million years after the chondrite St. Severin. The argon data show substantial loss of radiogenic Ar 40 and do not define an Ar 40 -Ar 39 plateau, establishing a lower limit K-Ar age of 4.35 × 10 9 yr, relative to an assumed age of 4.60 × 10 9 yr for St. Severin. Comparison with strontium data for other eucrites and the chondrite Guareña suggests an interval of 220 million years between fractionation from a rubidium-rich reservoir and the final cooling of Petersburg. The calcium-rich achondrite Lafayette has no detectable decay products of either I 129 or Pu 244 , indicating a gas-retention formation time at least 350 million years after St. Severin. The current best value of the Pu 244 / U 238 ratio in the chondrite St. Severin at the time of its formation is 0.0154 ± 0.0014, 21 per cent higher than previously reported.

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