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The core of the Blue Ridge anticlinorium in northern Virginia

By
James W. Clarke
James W. Clarke
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Published:
January 01, 1984

Proterozoic Y and Z granitic rocks compose the core of the Blue Ridge anticlinorium in northern Virginia. The oldest units are the Flint Hill Gneiss; an augen-bearing gneiss; the “Pedlar Formation”; and a porphyroblastic granitic gneiss. These appear to have ages in the 1,000-m.y. to 1,100-m.y. range. The porphyroblastic granitic gneiss is in fault contact with the Flint Hill; the Flint Hill grades into the augen-bearing gneiss; and the “Pedlar” appears to be in gradational contact with the Flint Hill. The porphyroblastic granitic gneiss carries xenoliths of an older layered biotite gneiss that lie transverse to the foliation of the host gneiss. The 1,010-m.y.-old Marshall Metagranite intrudes the porphyroblastic granitic gneiss and the Flint Hill Gneiss. Granitic rocks of the 700-m.y.-old Robertson River Formation intrude the Flint Hill Gneiss, the augen-bearing gneiss, and the porphyroblastic granitic gneiss. All units of the core of the anticlinorium are cut by metabasaltic dikes, which are presumed to be feeder dikes for the younger metavolcanic rocks of the Catoctin Formation of the region. The presence of charnockitic rocks in the western part of the core of the anticlinorium indicates that a granulite grade of metamorphism was reached in this terrane. The absence of hypersthene in other rocks of the area may reflect only their chemical and mineral composition. The possibility exists that these disparate-facies rocks were juxtaposed tectonically.

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Contents

GSA Special Papers

The Grenville Event in the Appalachians and Related Topics

Mervin J. Bartholomew
Mervin J. Bartholomew
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Geological Society of America
Volume
194
ISBN print:
9780813721941
Publication date:
January 01, 1984

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