Abstract

The Coyah Granite of Guinea intruded western portions of the Rokelide orogen following a tectonothermal event at ca. 550 Ma. It records a biotite-muscovite plus whole-rock Rb-Sr isochron age of 533 ± 7 m.y. (MSWD = 1.6) which is interpreted to closely date crystallization. The Osceola Granite represents a major lithotectonic element in the pre-Cretaceous crystalline basement of peninsular Florida. Five biotite concentrates from cuttings recovered from four wells penetrating the pluton record 40Ar/39Ar plateau ages ranging between 527.4 ± 1.9 m.y. and 534.6 ± 2.0 m.y. Petrographic characteristics of the four samples suggest relatively rapid post-magmatic cooling, and the plateau ages are interpreted to closely date emplacement of the pluton. Similarities in age and petrographic characteristics combine to suggest that the Coyah and Osceola Granites were initially part of a sequence of plutons emplaced along the northwestern margin of the Gondwana continent. Portions of this terrane amalgamated with Laurentia during late Paleozoic assembly of Pangea. Various exotic lithotectonic terranes which had previously accreted (or were at least proximal) to the North American Craton were transported to their present structural position in the southern-central Appalachian orogen during this collision.

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