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Petrology of impact melt rocks from the Chesapeake Bay crater, USA

By
Axel Wittmann
Axel Wittmann
Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA
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Ralf T. Schmitt
Ralf T. Schmitt
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany
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Lutz Hecht
Lutz Hecht
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany
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David A. Kring
David A. Kring
Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA
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W. Uwe Reimold
W. Uwe Reimold
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany
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Harold Povenmire
Harold Povenmire
Florida Institute of Technology, Melbourne, Florida 32901, USA
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Published:
January 2009

The Eyreville B drill core in the inner annular moat of the 85-km-diameter Ches-apeake Bay impact structure recovered the first coherent impact melt volumes from within the crater as two bodies, 1 and 5.5 m thick. This study focuses on the petrogenesis of these well-preserved rocks. Mixing calculations reveal that the chemical composition of these melts can be modeled as a hybrid of ~40% sedimentary target and ~60% crystalline basement component. The melt rocks contain abundant lithic and mineral clasts that display all stages of shock metamorphism. Zircon clasts record the cooling of the melt from temperatures above 1700 °C to below 1200 °C within the first minutes after formation. Glassy melt with a peraluminous, rhyolitic composition that contains ~5 wt% water is preserved. This melt records a crystallization sequence of aluminum-rich orthopyroxene and hercynitic spinel, followed by plagioclase, titano-magnetite and cordierite, and late sanidine. Spherulitic aluminosilicate-SiO2-cordierite aggregates that are comparable to buchites at temperatures below ~1465 °C complement this assemblage. Lack of hyaloclastic fragmentation suggests dry emplacement conditions. Complete cooling by conductive heat transfer took ~7 weeks and ~4 years for the 1-m- and the 5.5-m-thick melt bodies, respectively. Alteration stages below ~100 °C produced smectite, phillipsite, chalcedony, and a rare zeolite phase that is tentatively identified as terranovaite.

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Contents

GSA Special Papers

The ICDP-USGS Deep Drilling Project in the Chesapeake Bay impact structure: Results from the Eyreville Core Holes

Edited by
Gregory S. Gohn
Gregory S. Gohn
U.S. Geological Survey, Reston, Virginia, USA
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Christian Koeberl
Christian Koeberl
Department of Earth & Planetary Sciences, Rutgers University, USA
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Kenneth G. Miller
Kenneth G. Miller
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Germany
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Wolf Uwe Reimold
Wolf Uwe Reimold
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Germany
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Geological Society of America
Volume
458
ISBN print:
9780813724584
Publication date:
2009

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