Letter | Published:

Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa

Naturevolume 441pages203206 (2006) | Download Citation

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Abstract

Meteorites provide a sample of Solar System bodies and so constrain the types of objects that have collided with Earth over time. Meteorites analysed to date, however, are unlikely to be representative of the entire population and it is also possible that changes in their nature have occurred with time1. Large objects are widely believed to be completely melted or vaporized during high-angle impact with the Earth2,3. Consequently, identification of large impactors relies on indirect chemical tracers, notably the platinum-group elements4. Here we report the discovery of a large (25-cm), unaltered, fossil meteorite, and several smaller fragments within the impact melt of the giant (> 70 km diameter), 145-Myr-old Morokweng crater, South Africa. The large fragment (clast) resembles an LL6 chondrite breccia, but contains anomalously iron-rich silicates, Fe-Ni sulphides, and no troilite or metal. It has chondritic chromium isotope ratios and identical platinum-group element ratios to the bulk impact melt. These features allow the unambiguous characterization of an impactor at a large crater. Furthermore, the unusual composition of the meteorite suggests that the Morokweng asteroid incorporated part of the LL chondrite parent body not represented by objects at present reaching the Earth.

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Acknowledgements

This work was logistically supported by Business Venture Investments No. 33 (Pty) Ltd. (M.A.G.A). Financial support was provided by S.-J. Barnes, Canada Research Chair in Magmatic Ore Deposits, UQAC. In addition, analytical grants were provided by the University of Pretoria (W.D.M.), and by NASA (A.S. and G.W.L.). ICP analyses at Cardiff University were supported by the Leverhulme Trust (I.McD.) and by a JIF award from the NERC. A.J.B. is supported by NERC Services and Facilities funding to the Isotope Community Support Facility at SUERC. We thank H. Gregoire for assistance in producing the EMS images, and R. Ash and R. Burgess for comments on an early version of the manuscript. Author Contributions All co-authors contributed in the form of data generation and/or discussion and critical comment.

Author information

Affiliations

  1. Sciences de la Terre, Université du Québec à Chicoutimi, Quebec, G7H 2B1, Chicoutimi, Canada

    • W. D. Maier
    •  & M. D. Higgins
  2. Department of Geology, University of Pretoria, 0002, Pretoria, South Africa

    • W. D. Maier
    •  & P. Gräser
  3. South African Nuclear Energy Corporation, 0001, Pretoria, South Africa

    • M. A. G. Andreoli
  4. School of Geosciences, University of the Witwatersrand, Wits, South Africa, 2050

    • M. A. G. Andreoli
    •  & L. D. Ashwal
  5. School of Earth, Ocean & Planetary Sciences, Cardiff University, Cardiff, CF10 3YE, UK

    • I. McDonald
  6. Planetary Sciences, Cardiff University

    • I. McDonald
  7. Scottish Universities Environmental Research Centre, East Kilbride, G75 0QF, UK

    • A. J. Boyce
  8. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, 92093, USA

    • A. Shukolyukov
    •  & G. W. Lugmair
  9. Department of Geological Sciences, Indiana University, Bloomington, Indiana, 47405-7000, USA

    • E. M. Ripley
  10. Ithemba LABS - Gauteng, Wits, 2050, South Africa

    • R. J. Hart

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Competing interests

Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

Corresponding author

Correspondence to W. D. Maier.

Supplementary information

  1. Supplementary Table 1

    Whole rock data for Morokweng meteorite. (XLS 20 kb)

  2. Supplementary Table 2

    Composition of olivines, Morokweng meteorite. (XLS 42 kb)

  3. Supplementary Table 3

    Composition of orthopyroxenes, Morokweng meteorite. (XLS 38 kb)

  4. Supplementary Table 4

    Composition of plagioclase, Morokweng meteorite (XLS 20 kb)

  5. Supplementary Table 5

    Chromite compositions: Morokweng meteorite (XLS 16 kb)

  6. Supplementary Table 6

    Composition of pyrrhotite and pentlandite in Morokweng meteorite. (XLS 17 kb)

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https://doi.org/10.1038/nature04751

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