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U-Th-Pb and Rb-Sr systematics of Apollo 17 boulder 7 from the North Massif of the Taurus-Littrow Valley

Earth and Planetary Science Letters

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Abstract

Portions of highland breccia boulder 7 collected during the Apollo 17 mission were studied using UThPb and RbSr systematics. A RbSr internal isochron age of 3.89 ?? 0.08 b.y. with an initial 87Sr/86Sr of 0.69926 ?? 0.00008 was obtained for clast 1 (77135,57) (a troctolitic microbreccia). A troctolitic portion of microbreccia clast 77215,37 yielded a UPb internal isochron of 3.8 ?? 0.2 b.y. and an initial 206Pb/207Pb of 0.69. These internal isochron age are interpreted as reflecting metamorphic events, probably related to impacts, which reset RbSr and UPb mineral systems of older rocks. Six portions of boulder 7 were analyzed for U, Th, and Pb as whole rocks. Two chemical groups appear to be defined by the U, Th, and Pb concentration data. Chemical group A is characterized by U, Th, and Pb concentrations and 238U/204Pb values which are higher than those of group B. Group A rocks have typical 232Th/238U ratios of ??? 3.85, whereas-group B rocks have unusually high Th/U values of ??? 4.1. Whole-rock UPb and PbPb ages are nearly concordant. Two events appear to be reflected in these data - one at ??? 4.4 b.y. and one at ??? 4.5 b.y. The chemical groupings show no correlation with documented ages. The old ages of ??? 4.4 b.y. and ??? 4.5 b.y. may, like the younger ??? 4.0 b.y. ages, be related to basin excavation events. ?? 1974.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
U-Th-Pb and Rb-Sr systematics of Apollo 17 boulder 7 from the North Massif of the Taurus-Littrow Valley
Series title:
Earth and Planetary Science Letters
Volume
23
Issue:
3
Year Published:
1974
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Earth and Planetary Science Letters
First page:
445
Last page:
452
Number of Pages:
8