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Geochemistry of impactites and crystalline basement-derived lithologies from the ICDP-USGS Eyreville A and B drill cores, Chesapeake Bay impact structure, Virginia, USA

By
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 Lithospheric Research, Center for Earth Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
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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, Private Bag 3, PO Wits, Johannesburg, 2050, South Africa
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Dieter Mader
Dieter Mader
Department of Lithospheric Research, Center for Earth Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
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Axel Wittmann
Axel Wittmann
Museum für Naturkunde–Leibniz Institute at Humboldt University Berlin, Invalidenstrasse 43, 10115 Berlin, Germany, and Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, Texas 77058, USA
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Christian Koeberl
Christian Koeberl
Department of Lithospheric Research, Center for Earth Sciences, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
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Roger L. Gibson
Roger L. Gibson
Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, PO Wits, Johannesburg, 2050, South Africa
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Published:
January 2009

We investigated whole-rock chemical compositions of 318 samples of Exmore breccia (diamicton), impactite (suevite, impact melt rock, polymict lithic impact breccia), and crystalline basement-derived rocks from 444 to 1766 m depth in the International Continental Scientific Drilling Program (ICDP)–U.S. Geological Survey (USGS) Eyreville A and B drill cores (Chesapeake Bay impact structure, Virginia, USA). Here, we compare the average chemical compositions for the Exmore breccia (diamicton), the impactites and their subunits, sandstone, granite, granitic gneiss, and amphibolite of the lithic block section (1095.7–1397.2 m depth), cataclastic gneiss of the impact breccia section, and schist and pegmatite/granite of the basal crystalline section (1551.2–1766.3 m depth). The granite of the megablock (1097.7–1371.1 m depth) is of I-type and is seemingly related to a syncollisional setting. The amphibolite (1377.4–1387.5 m depth) of the lithic block section is of igneous origin and has a tholeiitic character. Based on chemical composition, the Exmore breccia (diamicton) can be subdivided into five units (444.9–450.7, 450.7–468, 468–518, 518–528, and 528–~865 m depth). The units in the depth intervals of 450.7–468 and 518–528 m are enriched in TiO2, MgO, Sc, V, Cr, and Zn contents compared to the other Exmore breccia units. In some samples, especially at ~451–455 m depth, the Exmore breccia contains significant amounts of P2O5. The Exmore breccia is recognized as a mixture of all sedimentary and crystalline target components, and, when compared to the impactites, it contains a significant amount of a SiO2-rich target component of sedimentary origin. The chemical composition of the impactites overlaps the compositional range for the Exmore breccia. The impactites generally display a negative correlation of SiO2 and CaO, and a positive correlation of TiO2, Al2O3, Fe2O3, and MgO with depth. This is the result of an increasing basement schist component, and a decreasing sedimentary and/or granitic component with depth. Suevite units S2 and S3 display distinct enrichment of Na2O by a factor of ~2 compared to all other impactite units, which is interpreted to reflect a higher granitic component in these units.

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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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