U-Th-Pb systematics of some Apollo 16 lunar samplesU, Th, and Pb concentrations and lead isotopic compositions of Apollo 16 samples are interpreted as follows: (1) an early period of lunar differentiation of either global or regional scale occurred about 4.47 b.y. ago; (2) the Imbrian impact event affected many Apollo 16 samples about 3.99 b.y. ago; (3) some Apollo 16 metaclastic rocks and breccias contain a large amount of KREEP-like material; (4) lead produced in the early history of the moon has been concentrated in lunar highland soils yielding high Pb-207/Pb-206 ratios corresponding to apparent ages of more than 4.8 b.y.; and (5) South Ray Crater soils reflect the approximately 2-b.y.-old event previously proposed for the Apollo 12 and 14 samples.
Document ID
19740040176
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Nunes, P. D.
Tatsumoto, M.
Knight, R. J.
Unruh, D. M.
Doe, B. R. (U.S. Geological Survey Denver, Colo., United States)