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Evolution of crystalline target rocks and impactites in the Chesapeake Bay impact structure, ICDP-USGS Eyreville B core

By
J. Wright Horton, Jr.
J. Wright Horton, Jr.
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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Michael J. Kunk
Michael J. Kunk
U.S. Geological Survey, MS 926A, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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Harvey E. Belkin
Harvey E. Belkin
U.S. Geological Survey, MS 956, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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John N. Aleinikoff
John N. Aleinikoff
U.S. Geological Survey, MS 963, Denver Federal Center, Denver, Colorado 80225, USA
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John C. Jackson
John C. Jackson
U.S. Geological Survey, MS 954, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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I-Ming Chou
I-Ming Chou
U.S. Geological Survey, MS 954, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
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Published:
January 01, 2009

The 1766-m-deep Eyreville B core from the late Eocene Chesapeake Bay impact structure includes, in ascending order, a lower basement-derived section of schist and pegmatitic granite with impact breccia dikes, polymict impact breccias, and cataclas tic gneiss blocks overlain by suevites and clast-rich impact melt rocks, sand with an amphibolite block and lithic boulders, and a 275-m-thick granite slab overlain by crater-fill sediments and postimpact strata. Graphite-rich cataclasite marks a detachment fault atop the lower basement-derived section. Overlying impactites consist mainly of basement-derived clasts and impact melt particles, and coastal-plain sediment clasts are underrepresented. Shocked quartz is common, and coesite and reidite are confirmed by Raman spectra. Silicate glasses have textures indicating immiscible melts at quench, and they are partly altered to smectite. Chrome spinel, baddeleyite, and corundum in silicate glass indicate high-temperature crystallization under silica undersaturation. Clast-rich impact melt rocks contain α-cristobalite and monoclinic tridymite. The impactites record an upward transition from slumped ground surge to melt-rich fallback from the ejecta plume. Basement-derived rocks include amphibolite-facies schists, greenschist(?)-facies quartz-feldspar gneiss blocks and subgreenschist-facies shale and siltstone clasts in polymict impact breccias, the amphibolite block, and the granite slab. The granite slab, underlying sand, and amphibolite block represent rock avalanches from inward collapse of unshocked bedrock around the transient crater rim. Gneissic and massive granites in the slab yield U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dates of 615 ± 7 Ma and 254 ± 3 Ma, respectively. Postimpact heating was <~350 °C in the lower basement-derived section based on undisturbed 40Ar/39Ar plateau ages of muscovite and <~150 °C in sand above the suevite based on 40Ar/39Ar age spectra of detrital microcline.

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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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