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Shock metamorphism of siliceous volcanic rocks of the El'gygytgyn impact crater (Chukotka, Russia)

By
Eugene P. Gurov
Eugene P. Gurov
Institute of Geological Sciences, National Academy of Sciences of the Ukraine, 55b Oles Gontchar Street, Kiev 01054, Ukraine
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Christian Koeberl
Christian Koeberl
Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, AustriaCorresponding author: christian.koeberl@univie.ac.at.
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Wolf Uwe Reimold
Wolf Uwe Reimold
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa
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Franz Brandstätter
Franz Brandstätter
Natural History Museum, P.O. Box 417, A-1014 Vienna, Austria
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Kassa Amare
Kassa Amare
Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
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Published:
January 01, 2005

The 18-km-diameter El'gygytgyn crater is located on the Chukotka peninsula, northeastern Russia. It represents the only currently known impact structure formed in siliceous volcanics, including tuffs. The impact melt rocks and target rocks provide an excellent opportunity to study shock metamorphism of volcanic rocks. The shock-induced changes observed in porphyritic volcanic rocks from El'gygytgyn can be applied to a general classification of shock metamorphism of siliceous volcanic rocks.

Strongly shocked volcanic rocks with phenocrysts converted to diaplectic quartz glass and partially melted feldspars as well as cryptocrystalline matrices are widespread in the El'gygytgyn crater. In particular, the following different stages of shock metamorphism are observed: (i) weakly to moderately shocked lavas and tuffs with phenocrysts and clasts of quartz and feldspars; (ii) moderately shocked volcanic rocks and tuffs with diaplectic glasses of quartz and feldspars; (iii) strongly shocked lavas and tuffs with phenocrysts of diaplectic quartz glass and fused glasses of feldspars in melted matrixes; and (iv) impact melt rocks and impact glasses. In addition, thin glassy coatings of voids in impact melt rocks have been observed.

While the shock-induced changes of clasts of framework silicates in these volcanic rocks do not differ from respective changes in other crystalline rocks, the fine-grained matrix of porphyritic rocks is converted into fused glass at the same shock pressures as feldspar minerals. No remnants of fine-grained quartz are preserved in matrix converted into fused glass by shock.

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Contents

GSA Special Papers

Large Meteorite Impacts III

Thomas Kenkmann
Thomas Kenkmann
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Friedrich Hörz
Friedrich Hörz
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Alex Deutsch
Alex Deutsch
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Geological Society of America
Volume
384
ISBN print:
9780813723846
Publication date:
January 01, 2005

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