Abstract

New compilations of geometry and tectonic transport in the Pennsylvania salient suggest that these features continue uninterrupted from the Piedmont through the Valley and Ridge provinces. These data are the basis for a new two-azimuth transport model for origin of the curvature. Edge geometry of an Eocambrian craton and a thickened stratigraphy acted as templates for Alleghanian regional décollement, first as Reading Prong ∼N35°W motion, followed by ∼N68°W Blue Ridge motion. Both displacements involved some drag rotation and overprinting in a central zone. This model avoids the problem of minimal tangential stretching, explains the anthracite basins as trailing-edge graben and basin structures against the autochthonous Pocono Plateau, and produces the Nittany-Juniata culmination as an overprinted pileup of duplexes in the central zone. The model of detachment followed by changing azimuth of motion of a megadécollement sheet may apply to other salients throughout the world.

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