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

Maier Wolfgang D., Andreoli Marco A.G., McDonald Iain, Higgins Michael D., Boyce A. J., Shukolyukov A., Lugmair G. W., Ashwal Lewis D., Gräser P., Ripley Edward M. et Hart R.J.. (2006). Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa. Nature, 441, p. 203-206.

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URL officielle: https://www.nature.com/articles/nature04751

Résumé

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.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:441
Pages:p. 203-206
Version évaluée par les pairs:Oui
Date:11 Mai 2006
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:astéroïde, cratère, Afrique du Sud
Déposé le:16 juill. 2018 19:36
Dernière modification:16 juill. 2018 19:36
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