Noble gas investigations of lunar rocks 10017 and 10071
The noble gases He, Ne, Ar, Kr and Xe and also K and Ba were measured in the Apollo 11 igneous rocks 10017 and 10071, and in an ilmenite and two feldspar concentrates separated from rock 10071. Whole rock K/Ar ages of rocks 10017 and 10071 are (2350 plus or minus 60) x 10/sup 6/ yr and (2880 plus or minus f 60) x 10/sup 6/ yr, respectively. The two feld spar concentrates of rock 10071 have distinctly higher ages: (3260 plus or minus 60) x 10/sup 6/ yr and (3350 plus or minus 70) x 10/sup 6/ yr. These ages are st ill 10 percent lower than the Rb/ Sr age obtained by Papanastassiou et al., ( Earth Planet. Sei. Lett.; 8: 1 to 19 (1970)) and some /sup 40/Ar diffusion loss must have occurred even in the relatively coarsegrained feldspar. The relative abundance patterns of spallation Ne, Ar, Kr, and Xe are in agrecment with the ratios predicted from meteoritic preduction rates. However, diffusion loss of spallation /sup 3/He is evident in the whole rock samples, and even more in the feldspar concentrates. The ilmenite shows little or no diffusion loss. The isotopic composition of spallation Kr and Xe is similar to the one observed in meteorites. Small, systematic differences in the spallation Kr spectra of rocks 10017 and 10071 are due to variations in the irradiation hardness (shielding). The Kr spallation spectra in the mineral concentrates are different from the whole rock spectra and also show individual variations, reflecting the differences in target element composition. The relative abundance of cosmic ray produced /sup 131/Xe differs by nearly 50 percent in the two rocks. The other Xe isotopes show no variations of similar magnitude. The origin of the /sup 131/Xe yield variability is discussed. /sup 81/Kr was measured in all the samples investigated. The /sup 81/Kr/Kr exposure ages of rocks 10017 and 10071 are (480 plus or minus 25) x 10/sup 6/yr and (350 plus or minus 15) x 10/sup 6/ yr, respectively. Exposure ages derived from spallation /sup 21/Ne, /sup 38/Ar, /sup 83/Kr, and /sup 126/Xe are essentially in agreement with the /sup 81/Kr/Kr ages. The age of rock 10071 might be somewhat low because of a possible recent exposure of the sample to solar flare particles. (auth)
- Research Organization:
- Univ., Bern
- NSA Number:
- NSA-29-022103
- OSTI ID:
- 4342677
- Journal Information:
- Geochim. Cosmochim. Acta, v. 38, no. 1, pp. 97-120, Other Information: Orig. Receipt Date: 30-JUN-74; Bib. Info. Source: UK (United Kingdom (sent to DOE from))
- Country of Publication:
- United Kingdom
- Language:
- English
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