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An overview of the Grenville basement complex of the Pine Mountain window, Alabama and Georgia

James W. Sears
James W. Sears
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Robert B. Cook, Jr.
Robert B. Cook, Jr.
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January 01, 1984

Grenville basement rocks and their metasedimentary cover are exposed in the Pine Mountain window of Georgia and Alabama. The Grenville complex of the window includes charnockite, charnockite gneiss, feldspathic and migmatitic augen gneiss, and mylonite. The metasedimentary cover, the Pine Mountain Group, consists of an approximately 2 km-thick sequence of aluminous and graphitic schist, orthoquartzite and dolomitic marble.

Schistosity of the Grenville rocks conforms to that of the enclosing Pine Mountain Group, is parallel to compositional layering and the basement-cover interface, and is the axial surface of the Auburn, Memory Hill, and Thomaston nappes. In Alabama, the basement-cover interface was refolded coaxially about a N70E axis so that the axial surfaces of the major fold-nappes are folded isoclinally. To the northeast, complex interference folding resulted in development of broad basins and domes and curvilinear axial traces of folds of foliation. An apparent increase in strain to the southwest closely corresponds to the appearance of thick sheets of basement-derived mylonite and an increase in metamorphic grade from kyanite-garnet-muscovite-staurolite-biotite in Georgia to sillimanite-biotite-muscovite-anatectite in Alabama.

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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
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Publication date:
January 01, 1984



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