Abstract
Age determinations of impact-produced materials in brecciated meteorites1 are particulary important for understanding the evolutionary history of meteorites. The age characteristics of these meteorites have been examined mostly by the K–Ar method or, in a few cases2, by the Rb–Sr method. However, age data are still rare and, except for a few cases3, the large-ion lithophile (LIL) trace-element chemical features have not been studied in detail. In this respect, the Yamato-79 shocked meteorites are the best specimens for investigation. We report here results of Rb–Sr systematics and trace-element analyses for an almost wholly impact-melted LL-chondrite, Y-790964, one of the Yamato-79 unusual chondrites. The analyses yield an internal isochron age of 1,200±50 (2σ) Myr. The isotopic and trace-element data obtained represent the first clear evidence of the youngest impact-melting and LIL-element fractionations for a complete LL-chondrite, and suggest that the 1,200-Myr-age is a non-trivial marker in the evolution of meteorites.
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Nakamura, N., Okano, O. 1,200-Myr impact-melting age and trace-element chemical features of the Yamato-790964 chondrite. Nature 315, 563–566 (1985). https://doi.org/10.1038/315563a0
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DOI: https://doi.org/10.1038/315563a0
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