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Progressive mixing of meteoritic veneer into the early Earth’s deep mantle

Nature volume 460, pages 620–623 (2009)Cite this article

Abstract

Komatiites are ancient volcanic rocks, mostly over 2.7 billion years old (from the Archaean era), that formed through high degrees of partial melting of the mantle and therefore provide reliable information on bulk mantle compositions1. In particular, the platinum group element (PGE) contents of komatiites provide a unique source of information on core formation, mantle differentiation and possibly core–mantle interaction2,3,4,5,6,7,8. Most of the available PGE data on komatiites are from late Archaean (∼2.7–2.9 Gyr old) or early Proterozoic (2.0–2.5 Gyr old) samples. Here we show that most early Archaean (3.5–3.2 Gyr old) komatiites from the Barberton greenstone belt of South Africa and the Pilbara craton of Western Australia are depleted in PGE relative to late Archaean and younger komatiites. Early Archaean komatiites record a signal of PGE depletion in the lower mantle, resulting from core formation. This signal diminishes with time owing to progressive mixing-in to the deep mantle of PGE-enriched cosmic material that the Earth accreted as the ‘late veneer’ during the Early Archaean (4.5–3.8 Gyr ago) meteorite bombardment.

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Figure 1: PGE contents in Pilbara and Barberton komatiites.
Figure 2: Diagram of Pt and Ru versus age of komatiites.

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Acknowledgements

We thank D. Savard for the PGE analysis, and E. Hanski for comments. We also thank N. Arndt and H. Becker for reviews. This study was partly funded by the ARC (to M.L.F.), the University of Western Australia (to W.D.M.), CSIRO (to S.J.B.) and NSERC (to S.-J.B.). P.P. acknowledges support from the Geological Survey of Finland (GTK).

Author Contributions W.D.M., S.J.B., M.L.F., P.P. and R.H.S. provided samples and data, S.-J.B. analysed the South African and Pilbara samples, the first four authors provided the interpretation, and all co-authors contributed in the form of discussion and critical comment.

Author information

Authors and Affiliations

  1. Department of Geology, University of Oulu, Linnanmaa, 90014 Oulu, Finland,

    Wolfgang D. Maier

  2. Centre for Exploration Targeting, University of Western Australia, 35 Stirling Highway, Crawley 6009, Australia ,

    Wolfgang D. Maier & Marco L. Fiorentini

  3. CSIRO, 26 Dick Perry Avenue, Kensington 6151, Western Australia, Australia ,

    Stephen J. Barnes

  4. Research School of Earth Sciences, Australian National University, Canberra 0200, Australian Capital Territory, Australia ,

    Ian H. Campbell

  5. Geological Survey of Finland, Betonimiehenkuja 4, Espoo 02151, Finland ,

    Petri Peltonen

  6. Department of Geology, University of Helsinki, Gustaf Hällströmin katu 2a, Helsinki 00014, Finland,

    Petri Peltonen

  7. Sciences Appliques, Université du Québec à Chicoutimi, Chicoutimi G7H 2B1, Québec, Canada ,

    Sarah-Jane Barnes

  8. Geological Survey of Western Australia, 100 Plain Street, East Perth 6004, Western Australia, Australia ,

    R. Hugh Smithies

Authors
  1. Wolfgang D. Maier
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Corresponding author

Correspondence to Wolfgang D. Maier.

Supplementary information

Supplementary Information

This file contains Supplementary Methods, Supplementary Figures 3 - 4 with Legends and Supplementary References. (PDF 2187 kb)

Supplementary Table 1

This file contains the whole rock data of the Barberton samples. (XLS 59 kb)

Supplementary Table 2

This file contains the whole rock data of the Pilbara samples. (XLS 27 kb)

Supplementary Table 3

This file contains the analytical accuracy and precision. (XLS 16 kb)

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Maier, W., Barnes, S., Campbell, I. et al. Progressive mixing of meteoritic veneer into the early Earth’s deep mantle. Nature 460, 620–623 (2009). https://doi.org/10.1038/nature08205

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