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Rb-Sr ages and initial strontium in basalts from Apollo 15

Papanastassiou, D. A. and Wasserburg, G. J. (1973) Rb-Sr ages and initial strontium in basalts from Apollo 15. Earth and Planetary Science Letters, 17 (2). pp. 324-337. ISSN 0012-821X. doi:10.1016/0012-821x(73)90197-0.

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Internal isochrons have been determined for six basalts returned by the Apollo 15 mission. The rocks represent each of the major sampling stops during Apollo 15. The ranges in age and I are 3.28 ± 0.04 to 3.44 ± 0.07AE and 0.69923 ± 6 to 0.69937 ± 4. The range in I is very narrow and appears to represent a rather uniform magma source. A detailed study of the initial ⁸⁷Sr/⁸⁶Sr was made on geometrically distinct pieces of 15555. The I value was demonstrated to be well defined to within 3 × 10⁻⁵ and therefore reports of variations in I for this rock are in error. The close similarity in the ages of basalts from both the Apollo 12 and 15 sites indicates that widespread extrusion of basaltic lavas took place at 3.2–3.3 AE. From all of the evidence currently available, the last major episode of mare flows took place at 3.16 ± 0.09AE. No clear demonstration of major extrusions subsequent to this time has yet been found. The onset of mare flooding must have begun prior to 3.7 AE. All the results to date show that subsequent to the formation of the Moon the lunar basalts evolved in a magma reservoir with Rb/Sr ∼ 10⁻² and cannot be derived from a mantle which has a chondritic Rb/Sr.

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Wasserburg, G. J.0000-0002-7957-8029
Additional Information:We thank A.L. Albee and A. Gancarz for the microprobe studies in conjunction with this work. Theodore Wen set up and followed through with the development of the small column chemistry. This work was supported by NASA under NAS 9-8074.
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NASANAS 9-8074
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Caltech Division of Geological and Planetary Sciences2201
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ID Code:118038
Deposited By: Tony Diaz
Deposited On:02 Dec 2022 18:40
Last Modified:02 Dec 2022 18:40

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