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Petrographic and geochemical comparisons between the lower crystalline basement-derived section and the granite megablock and amphibolite megablock of the Eyreville B core, Chesapeake Bay impact structure, USA

By
Gabrielle N. Townsend
Gabrielle N. Townsend
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa
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Roger L. Gibson
Roger L. Gibson
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa
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J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, 926A National Center, Reston, Virginia 20192, USA
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Wolf Uwe Reimold
Wolf Uwe Reimold
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany, and Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, P.O. WITS, Johannesburg 2050, South Africa
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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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Katerina Bartosova
Katerina Bartosova
Department of Geological Sciences, University of Vienna, Althanstrasse 14, Vienna A-1090, Austria
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Published:
January 01, 2009

The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ± fibrolite ± garnet ± tourmaline ± pyrite ± rutile ± pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite-K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase-quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ± biotite ± garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ± muscovite ± pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ± epidote ± amphibole.

The lower basement-derived section and both megablocks exhibit similar middle- to upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafic source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites.

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GSA Special Papers

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

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:
January 01, 2009

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