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Published January 1970 | public
Book Section - Chapter

O¹⁸/O¹⁶ ratios of Apollo 11 lunar rocks and minerals


Oxygen isotope analyses were obtained on coexisting minerals in 5 lunar microgabbros and basalts. The δO¹⁸ values are: cristobalite (+7·16), plagioclase (+6-06 to +6·33), clinopyroxene (+5·67 to + 5·95), and ilmenite (+3·85 to +4·12). The uniformity of δO¹⁸ suggests a close approach to isotopic equilibrium, with a calculated temperature of formation of about 1200°C, or about the same as terrestrial basalts. These rocks must have crystallized rapidly at low P_(H₂O), as they show no evidence of further oxygen isotope exchange during cooling. The lunar fines and breccias are 0·5 per mil richer in O¹⁸ than the above rocks, indicating addition of an O¹⁸-rich constituent (perhaps carbonaceous chondrites), and/or that O¹⁶ was depleted by vapor fractionation during formation of the abundant glass in these materials. The lunar rocks are very similar in δO¹⁸ to terrestrial mafic and ultramafic igneous rocks and to the chondritic meteorites, suggesting a genetic relationship. However, they are significantly richer in O¹⁸ than several other meteorite groups, such as the basaltic achondrites. The O¹⁸ data also indicate that tektites are unlikely to have originated on the moon.

Additional Information

Sample 10017 was provided by D. S. BURNETT and G. J. WASSERBURG. Some of the laboratory work was done by P. YANAGISAWA. This research was supported by National Aeronautics and Space Administration Contract No. NAS 9-7944.

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