Early history of Earth's crust-mantle system inferred from hafnium isotopes in chondrites

Martin Bizzarro, Henning Haack, M. Rosing, J.A. Baker, D. Ulfbeck

    Research output: Contribution to journalJournal articleResearchpeer-review

    170 Citations (Scopus)

    Abstract

    The Lu to Hf decay series has been widely used to understand the nature of Earth's early crust-mantle system. The interpretation, however, of Lu-Hf isotope data requires accurate knowledge of the radioactive decay constant of Lu (¿176), as well as bulk-Earth reference parameters. A recent calibration of the ¿176 value calls for the presence of highly unradiogenic hafnium in terrestrial zircons with ages greater than 3.9 Gyr, implying widespread continental crust extraction from an isotopically enriched mantle source more than 4.3 Gyr ago, but does not provide evidence for a complementary depleted mantle reservoir. Here we report Lu-Hf isotope measurements of different Solar System objects including chondrites and basaltic eucrites. The chondrites define a Lu-Hf isochron with an initial Hf/Hf ratio of 0.279628 ± 0.000047, corresponding to ¿176 = 1.983 ± 0.033 x 10yr using an age of 4.56 Gyr for the chondrite-forming event. This ¿176 value indicates that Earth's oldest minerals were derived from melts of a mantle source with a time-integrated history of depletion rather than enrichment. The depletion event must have occurred no later than 320 Myr after planetary accretion, consistent with timing inferred from extinct radionuclides.
    Original languageEnglish
    JournalNature
    Volume421
    Issue number6926
    Pages (from-to)931-933
    Number of pages3
    ISSN0028-0836
    DOIs
    Publication statusPublished - 2003

    Cite this