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Experimental alteration of artificial and natural impact melt rock from the Chesapeake Bay impact structure

By
Julien Declercq
Julien Declercq
Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, NO 316, Norway
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Henning Dypvik
Henning Dypvik
Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, NO 316, Norway
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Per Aagaard
Per Aagaard
Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, NO 316, Norway
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Jens Jahren
Jens Jahren
Department of Geosciences, University of Oslo, P.O. Box 1047, Oslo, NO 316, Norway
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Ray E. Ferrell, Jr.
Ray E. Ferrell, Jr.
Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA
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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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Published:
January 01, 2009

The alteration or transformation of impact melt rock to clay minerals, particularly smectite, has been recognized in several impact structures (e.g., Ries, Chicxulub, Mjølnir). We studied the experimental alteration of two natural impact melt rocks from suevite clasts that were recovered from drill cores into the Chesapeake Bay impact structure and two synthetic glasses. These experiments were conducted at hydrothermal temperature (265 °C) in order to reproduce conditions found in melt-bearing deposits in the first thousand years after deposition. The experimental results were compared to geochemical modeling (PHREEQC) of the same alteration and to original mineral assemblages in the natural melt rock samples.

In the alteration experiments, clay minerals formed on the surfaces of the melt particles and as fine-grained suspended material. Authigenic expanding clay minerals (saponite and Ca-smectite) and vermiculite/chlorite (clinochlore) were identified in addition to analcime. Ferripyrophyllite was formed in three of four experiments. Comparable minerals were predicted in the PHREEQC modeling. A comparison between the phases formed in our experiments and those in the cores suggests that the natural alteration occurred under hydrothermal conditions similar to those reproduced in the experiment.

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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

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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