| Abstract: | This paper reports the results of thermal-release argon analyses of neutron-irradiated samples of the two nakhlite meteorites, Lafayette and Nakhla. The initiation of retention of radiogenic40Ar in Lafayette appears to have been a reasonably well-defined event which occurred (1.33 ± 0.03) × 109 yr ago, as determined by the40Ar-39Ar method. Nakhla also appears to have been retaining argon no longer than 1.3 × 109 yr, but its gas-retention age cannot be considered well-defined because its apparently most-retentive sites have nominal gas-retention ages shorter than those of the less-retentive sites which contain most of its potassium. |
