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On the age of KREEPIt is noted that the variable Rb-Sr model ages of lunar highland rocks containing a significant amount of KREEP basalt may be best explained by some fractionation of Rb from Sr during metamorphism 3.9 billion years ago, but the uniformity of the KREEP-type trace-element pattern in different highland samples indicates that elements such as the rare earth were hardly fractionated at all during the metamorphic event. Data are presented which show that the Rb/Sr fractionation 3.9 billion years ago was due to Rb mobilization alone in most cases and that this fractionation can be accounted for by coupling of Rb to other, less volatile incompatible elements. Variations of Rb in lunar highland rocks are analyzed, a correction method is applied for the Rb/Sr fractionation, and results are evaluated separately for Apollo 16 VHA and KREEP basalts, Apollo 17 noritic breccias, Apollo 14 KREEP breccias, Apollo 15 KREEP basalts, and Apollo 15-KREEP-enriched breccias. Evidence for volatilization of alkalis from glasses of impact origin is summarized, and an apparent correlation is discussed between meteoritic component (as given by the Ir/Au ratio) and rock type (as given by the U or Rb content) for many lunar highland samples.
Document ID
19780032326
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Palme, H.
(Chicago, University Chicago, Ill., United States)
Date Acquired
August 9, 2013
Publication Date
December 1, 1977
Publication Information
Publication: Geochimica et Cosmochimica Acta
Volume: 41
Subject Category
Lunar And Planetary Exploration
Accession Number
78A16235
Funding Number(s)
CONTRACT_GRANT: NGL-14-001-167
Distribution Limits
Public
Copyright
Other

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