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U-Th-Pb systematics of some Apollo 17 lunar samples and implications for a lunar basin excavation chronologyU, Th, and Pb concentrations and lead isotopic compositions of selected Apollo 17 soil and rock samples are presented. Concordia treatments of U-Pb whole samples of Apollo 17 mare basalts and highland rocks probably reflect several early thermal events about 4.5 b.y. old more consistently than do U-Pb ages of samples collected at other lunar sites. We propose that all lunar U-Th-Pb data reflect a multistate U-Pb evolution history most easily understood as being related to a complex planetesimal bombardment history of the moon which apparently dominated lunar events from about 4.5 to about 3.9 b.y. ago. Semi-distinct events at about 4.0, about 4.2, and 4.4-4.5 b.y. are evident on whole-rock frequency versus Pb-207/Pb-206 age histograms. Each of these events may reflect multiple cratering episodes. For mare basalts, complete resetting of the source rock U-Pb systems owing to Pb loss relative to U was apparently often approached after a major planetesimal impact.
Document ID
19750055563
Acquisition Source
Legacy CDMS
Document Type
Conference Proceedings
Authors
Nunes, P. D.
Tatsumoto, M.
Unruh, D. M.
(U.S. Geological Survey Denver, Colo., United States)
Date Acquired
August 8, 2013
Publication Date
January 1, 1974
Subject Category
Lunar And Planetary Exploration
Meeting Information
Meeting: Lunar Science Conference
Location: Houston, TX
Start Date: March 18, 1974
End Date: March 22, 1974
Accession Number
75A39635
Funding Number(s)
CONTRACT_GRANT: NASA ORDER T-2407-A
Distribution Limits
Public
Copyright
Other

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