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Science 12 December 2008:
Vol. 322. no. 5908, pp. 1678 - 1681
DOI: 10.1126/science.1166283
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Reports

Shock Metamorphism of Bosumtwi Impact Crater Rocks, Shock Attenuation, and Uplift Formation

Ludovic Ferrière,1 Christian Koeberl,1* Boris A. Ivanov,2 Wolf Uwe Reimold3

Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by ~5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.

1 Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
2 Institute for Dynamics of Geospheres, Russian Academy of Sciences, Leninsky Prospect 38-1, 119334 Moscow, Russia.
3 Museum of Natural History (Mineralogy), Humboldt University, Invalidenstrasse 43, D-10115 Berlin, Germany.

* To whom correspondence should be addressed. E-mail: christian.koeberl{at}univie.ac.at

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Science. ISSN 0036-8075 (print), 1095-9203 (online)