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Evaporative differentiation of impact-produced melts: Laser-simulation experiments and comparison with impact glasses from the Logoisk crater

By
M.V. Gerasimov
M.V. Gerasimov
Space Research Institute, Russian Academy of Sciences, Profsoyuznaya Street, 84/32 Moscow, 117997, Russiamgerasim@mx.iki.rssi.ru
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O.I. Yakovlev
O.I. Yakovlev
Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin Street, 19, Moscow, 117975, Russia
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Yu.P. Dikov
Yu.P. Dikov
Institute of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetny pereulok, 35, Moscow, 109017, Russia
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F. Wlotzka
F. Wlotzka
Max-Plank-Institut für Chemie, Abteilung Kosmochemie, P.O. Box 3060, D-55020, Mainz, Germany
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Published:
January 01, 2005

Evaporative modification of silicates during impacts by large meteorites is the result of high-temperature processing of colliding silicate materials. There are still unresolved questions about the influence of vaporization on the chemical compositions of impact glasses. Here we present the results of experimental modeling of impact-related high-temperature pulse heating of silicates with compositions representative of Earth's crust. Trends involving differential volatilization of the main rock-forming elements were determined experimentally and compared with those predicted by thermodynamic equilibrium calculations. Our results indicate that impact-induced vaporization is significant for melts at temperatures of 3000–5000 K. As vaporization begins, melts lose Si, Fe, and alkalis and are enriched in Mg, Ca, Al, and Ti. With increased mass loss, melts start to lose Mg while Si and even Na can still be present. Still greater mass loss produces melts enriched in Ca, Al, and Ti. We then attempted to use the experimentally determined trends to look for signs of evaporative differentiation in impact glasses from the Logoisk structure (Byelorussia). Fresh impact glasses from suevites in the Logoisk crater have compositions that are in good agreement with the differentiation trends obtained both experimentally and via thermodynamic calculations in the range of 3000–5000 K. The most useful methods for recognizing evaporative differentiation in the natural glasses are the conservation of the initial Ca/Al ratio and the anti-correlation of Si and Al.

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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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