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Poster communications

Paleomagnetism and Mineralogy of Unusual Silicate Glasses and Baked Soils on the Surface of the Atacama Desert of Northern Chile: A Major Airburst Impact ~12ka ago?

Pierrick Roperch 1 Nicolas Blanco Millarca Valenzuela J. Gattacceca 2 Bertrand Devouard 2 Jean-Pierre Lorand 3 Andrew Tomlinson Cesar Arriagada 4 Pierre Rochette 2
1 GR - Géosciences Rennes
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
3 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
4 Departamento de Geologia
Abstract : Unusual silicate glasses were found in northern Chile in one of the driest place on earth, the Atacama Desert. The scoria-type melted rocks are littered on the ground at several localities distributed along a longitudinal band of about 50km. The silicate glasses have a stable natural remanent magnetization carried by fine-grained magnetite and acquired during cooling. At one locality, fine-grained overbank sediments were heated to form a 10 to 20 cm-thick layer of brick-type samples. Magnetic experiments on oriented samples demonstrate that the baked clays record a thermoremanent magnetization acquired in situ above 600°C down to more than 10cm depth and cooled under a normal polarity geomagnetic field with a paleointensity of 40µT. In some samples of the silicate glass, large grains of iron sulphides (troilite) are found in the glass matrix with numerous droplets of native iron, iron sulphides and iron phosphides indicating high temperature and strong redox conditions during melting. The paleomagnetic record of the baked clays and the unusual mineralogy of the silicate glasses indicate a formation mainly by in situ high temperature radiation. Paleomagnetic experiments and chemical analyses indicate that the silicate glasses are not fulgurite type rocks due to lightning events, nor volcanic glasses or even metallurgical slags related to mining activity. The existence of a well-developped baked clay layer indicates that the silicate glasses are not impact-related ejectas. The field, paleomagnetic and mineralogical observations support evidence for a thermal event likely related to a major airburst. The youngest calibrated 14C age on a charcoal sample closely associated with the glass indicates that the thermal event occurred around 12 to 13 ka BP. The good conservation of the surface effects of this thermal event in the Atacama Desert could provide a good opportunity to further estimate the threats posed by large asteroid airbursts.
Document type :
Poster communications
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https://hal-insu.archives-ouvertes.fr/insu-01265803
Contributor : Isabelle Dubigeon <>
Submitted on : Monday, February 1, 2016 - 3:37:01 PM
Last modification on : Wednesday, October 14, 2020 - 4:16:48 AM

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  • HAL Id : insu-01265803, version 1

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INSU | GR | OSUR | CNRS | UNIV-RENNES1 | UNIV-NANTES | UNIV-AMU | CDF | GR-PPDB | INRA | OSU-INSTITUT-PYTHEAS | CEREGE | UNIV-RENNES | UNIV-ANGERS | LPG | INRAE | TP | PSL

Citation

Pierrick Roperch, Nicolas Blanco, Millarca Valenzuela, J. Gattacceca, Bertrand Devouard, et al.. Paleomagnetism and Mineralogy of Unusual Silicate Glasses and Baked Soils on the Surface of the Atacama Desert of Northern Chile: A Major Airburst Impact ~12ka ago?. AGU Fall Meeting 2015, Dec 2015, San Francisco, United States. pp.NH11A-1882, 2015. ⟨insu-01265803⟩

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