Abstract

Paleozoic carbonates that cover the eastern half of the North American craton preserved a bedding-parallel shortening fabric up to 800 km away from the Appalachian-Ouachita orogenic front as recorded by mechanical twins in calcite. A strain fabric is present in 29 of 31 samples from three traverses within the flat-lying cratonic cover sequence: Jasper, Arkansas, to Minneapolis, Minnesota, Bluefield, West Virginia, to Madison, Wisconsin; and Albany, New York, to Hamilton, Ontario. Twinning is found only in Paleozoic carbonates and is absent in Cretaceous limestones. In the two southernmost traverses, the orientation of the principal shortening axis (e1) is perpendicular to the thrust front and parallel to the thrusting direction of the southern Appalachians and the Ouachitas. The magnitude of calcite shortening strain (<6%) and the calculated differential stress (<90 MPa) decrease exponentially away from the orogenic front until twinning is absent. The northernmost traverse shows greater complexity, probably of its location in the bend of the Appalachian trend. We conclude that the regional strain fabric preserved in the cratonic cover sequence of eastern North America was produced by late Paleozoic orogenic stresses of the Appalachian-Ouachita orogeny, and that compressive stresses was transmitted over distances greater than 1200 km away from the active plate margin.

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