Heterogeneous Hadean Hafnium: Evidence of Continental Crust at 4.4 to 4.5 Ga

Author:

Harrison T. M.12345,Blichert-Toft J.12345,Müller W.12345,Albarede F.12345,Holden P.12345,Mojzsis S. J.12345

Affiliation:

1. Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia.

2. Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California at Los Angeles, Los Angeles, CA 90095, USA.

3. Ecole Normale Supérieure, CNRS Unité Mixte de Recherche 5570, 69364 Lyon Cedex 7, France.

4. Department of Geology, Royal Holloway University of London, Egham, TW20 0EX, UK.

5. Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA.

Abstract

The long-favored paradigm for the development of continental crust is one of progressive growth beginning at ∼4 billion years ago (Ga). To test this hypothesis, we measured initial 176 Hf/ 177 Hf values of 4.01- to 4.37-Ga detrital zircons from Jack Hills, Western Australia. ϵ Hf (deviations of 176 Hf/ 177 Hf from bulk Earth in parts per 10 4 ) values show large positive and negative deviations from those of the bulk Earth. Negative values indicate the development of a Lu/Hf reservoir that is consistent with the formation of continental crust (Lu/Hf ≈ 0.01), perhaps as early as 4.5 Ga. Positive ϵ Hf deviations require early and likely widespread depletion of the upper mantle. These results support the view that continental crust had formed by 4.4 to 4.5 Ga and was rapidly recycled into the mantle.

Publisher

American Association for the Advancement of Science (AAAS)

Subject

Multidisciplinary

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