1. Sciences de la Terre, Université du Québec à Chicoutimi, Chicoutimi, Quebec G7H 2B1, Canada
2. Department of Geology, University of Pretoria, Pretoria 0002, South Africa
3. South African Nuclear Energy Corporation, Pretoria 0001, South Africa
4. School of Geosciences, University of the Witwatersrand, Wits 2050, South Africa
5. School of Earth, Ocean & Planetary Sciences, Cardiff University, Cardiff CF10 3YE, UK
6. Scottish Universities Environmental Research Centre, East Kilbride G75 0QF, UK
7. Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, USA
8. Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405-7000, USA
9. Ithemba LABS - Gauteng, Wits 2050, South Africa

Correspondence to: W. D. Maier^1,2 Correspondence and requests for materials should be addressed to W.D.M. (Email: wolfgang_maier@uqac.ca).

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 Earth^{2, 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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