Other
Scientific paper
Jan 1974
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1974gecoa..38...97e&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 38, Issue 1, pp.97-120
Other
6
Scientific paper
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 ± 60) × 10 6 yr and (2880 ± 60) × 10 6 yr, respectively. The two feldspar concentrates of rock 10071 have distinctly higher ages: (3260 ± 60) × 10 6 yr and (3350 ± 70) × 10 6 yr. These ages are still 10 per cent lower than the Rb/Sr age obtained by et al. (1970) and some Ar 40 diffusion loss must have occurred even in the relatively coarse-grained feldspar. The relative abundance patterns of spallation Ne, Ar, Kr and Xe are in agreement with the ratios predicted from meteoritic production rates. However, diffusion loss of spallation He 3 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 Xe 131 differs by nearly 50 per cent in the two rocks. The other Xe isotopes show no variations of similar magnitude. The origin of the Xe 131 yield variability is discussed. Kr 81 was measured in all the samples investigated. The Kr 81 /Kr exposure ages of rocks 10017 and 10071 are (480 ± 25) × 10 6 yr and (350 ± 15) × 10 6 yr, respectively. Exposure ages derived from spallation Ne 21 , Ar 38 , Kr 83 and Xe 126 are essentially in agreement with the Kr 81 /Kr ages. The age of rock 10071 might be somewhat low because of a possible recent exposure of our sample to solar flare particles.
Eberhardt Peter
Geiss Johannes
Graf H.
Grägler N.
Krähenbühl Urs
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