Xenon isotopes in lunar anorthosites, basalts and dunites.

The xenon abundances of basaltic and anorthositic lunar rocks have been investigated experimentally. Estimates are obtained of the concentrations of radiogenic, cosmogenic, and primary isotopes in highly metamorphic and slightly metamorphic rock samples. Temperature fractions of radiogenic Xe-129 were obtained by means of stepwise heating. Excessive amounts of Xe-136, Xe-134, Xe-132, and Xe-131 were also found. Some possible mechanisms for the occurrence of heavy xenon in planetary atmospheres are discussed. The large variations in the composition of xenon were attributed to the presence of a cosmogenic component formed by the spallation of barium nuclei by photons with energies in the range 100-700 MeV. Xenon release curves show that processes of metamorphism on the moon would be sufficient to account for the partial release of xenon at low-temperature.