Abstract: | We report the results of thermal-release argon analyses of neutron-irradiated green glass spherules separated from lunar sample 15426. The gas-retention age, as determined by the40Ar 39Ar method, is (3.38 ± 0.06) X 109yr. This age is similar to those of local mare basalts and distinct from the ages of Appenine Front samples recovered from the same region as 15426. Trapped argon is present in near-surface regions of the spherules, and can be resolved into at least two components requiring separate origins, a shallow (0.1 μ) component with40Ar/39Ar > 30, and a deeper (2 μ) component with 40Ar/36Ar= 2.9. The ratio of trapped40Ar to36Ar is higher than found in any lunar soil and suggests that the trapped gas was implanted early in the spherules' history. The cosmic-ray exposure age is 300 my. |