U-Th-Pb and Rb-Sr systematics of Apollo 17 boulder 7 from the North Massif of the Taurus-Littrow Valley
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Abstract
Portions of highland breccia boulder 7 collected during the Apollo 17 mission were studied using U
ThPb and RbSr systematics. A RbSr internal isochron age of3.89 ± 0.08b.y. with an initial87Sr/86Sr of0.69926 ± 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 of3.8 ± 0.2b.y. and an initial206Pb/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 and238U/204Pb values which are higher than those of group B. Group A rocks have typical232Th/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.
| 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 |
| DOI | 10.1016/0012-821X(74)90134-4 |
| Volume | 23 |
| Issue | 3 |
| Year Published | 1974 |
| Language | English |
| Publisher | Elsevier |
| Description | 8 p. |
| First page | 445 |
| Last page | 452 |
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