Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.492l&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 492
Computer Science
Chile, Iron Meteorites, Magnetic Properties, Meteorite Craters, Electron Probes, Glass, Mossbauer Effect, Petrography
Scientific paper
The Monturaqui impact crater in northern Chile was first described by Sanchez and Cassidy in 1966. Petrographic and electron microprobe study of the Monturaqui impactite was published by Bunch and Cassidy in 1972. Field investigations of the crater have not revealed any pieces of unaltered meteorite. However, from studies of the elemental composition of metal spherules embedded in the glass of the impactite the impacting body is identified as an iron meteorite. In our preliminary report we presented the results of an investigation of a piece of Monturaqui impactite using Mossbauer spectroscopy. In this work we will give further information obtained by Mossbauer spectroscopy. The results of electron microscopy and magnetic susceptibility measurements are also presented. In all, seven samples were studied. Iron in the Monturaqui impactite exists in magnetically ordered phases as well as in the paramagnetic states: (a) Magnetically ordered phases: slightly substituted maghemite; nonstoichiometric magnetite; and goethite, which at room temperature is partly in the super-paramagnetic state; and (b) Paramagnetic phases: silicate glass, and in some grains the presence of olivine was proved. The Mossbauer, electron microscopy, and magnetic susceptibility investigation reveal both primary and secondary features of the impactite. The molten glass became enriched in Fe (mainly in ferrous iron) relative to the granite as Fe was transferred from the molten droplets of Fe-Ni alloy. On quenching the alloy, droplets became embedded in the newly formed glass. Both the glass and alloy components can be identified. The Fe-Ni alloy spherules lying close to cracks in the glass have later weathered into a rather complex mixture of Ni-containing iron oxides.
Bentzon M. B.
Knudsen Jens Martin
Koch Bender Chr.
Lipka James J.
Madsen Morten Bo
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