A. L. Albee1, D. S. Burnett1, A. A. Chodos1, O. Eugster1, J. C. Huneke1, D. A. Papanastassiou1, F. A. Podosek1, G. P. Russ1, H. G. Sanz1, F. Tera1, G. J. Wasserburg1
1Charles Arms Laboratory of Geological Sciences, California Institute of Technology, Pasadena 91109
Tóm tắt
The
87
Rb-
87
Sr internal isochrons for five rocks yield an age of 3.65 ± 0.05 × 10
9
years which presumably dates the formation of the Sea of Tranquillity. Potassium-argon ages are consistent with this result. The soil has a model age of 4.5 × 10
9
years, which is best regarded as the time of initial differentiation of the lunar crust. A peculiar rock fragment from the soil gave a model age of 4.44 × 10
9
years. Relative abundances of alkalis do not suggest differential volatilization. The irradiation history of lunar rocks is inferred from isotopic measurements of gadolinium, vanadium, and cosmogenic rare gases. Spallation xenon spectra exhibit a high and variable
131
Xe/
126
Xe ratio. No evidence for
129
I was found. The isotopic composition of solar-wind xenon is distinct from that of the atmosphere and of the average for carbonaceous chondrites, but the krypton composition appears similar to average carbonaceous chondrite krypton.
