Pennsylvania salient of the Appalachians: A two-stage model for Alleghanian motion based on new compilations of Piedmont data
Donald U Wise, Mathew L Werner, 2004. "Pennsylvania salient of the Appalachians: A two-stage model for Alleghanian motion based on new compilations of Piedmont data", Orogenic curvature: Integrating paleomagnetic and structural analyses, Aviva J. Sussman, Arlo B. Weil
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This study proposes a model for the origin of the Pennsylvania salient of the Appalachians based on data compilations that challenge the currently popular one-stage transport model. A contour map of the numerical values of the changing local strikes of axial traces shows an elbow-like geometry passing seamlessly across both the Piedmont Province and the Valley and Ridge Province. A new compilation of 46 tectonic transport vectors derived from local studies in the Piedmont also shows direct continuation into patterns of published vectors in the Valley and Ridge Province. Two distinct transport vector populations, each normal to the strike of a linear segment on either side of the elbow, appear in both Taconian and Alleghanian data. The new model proposes that an Eocambrian corner of the craton acted as a template for several major Paleozoic nappe displacements on the craton, each normal to a linear segment of the elbow. The first Alleghanian motion, mostly east of the Susquehanna River, was N30–40E or normal to the strike of the Reading Prong segment. Slightly younger Alleghanian motion west of the river was N65–70W or normal to the evolving Blue Ridge segment. Overprinting, some drag rotation, and greater total uplift occurred in the axial region. The younger Blue Ridge mega-décollement terminated laterally to the NNE in Pennsylvania as a series of en echelon structures that produced the final shape of the Juniata/Nittany culmination, the downwarp of the greater Anthracite synclinorium, and the Shawangunk segment of the Kingston orocline. The model clearly needs additional testing but is in accord with the observed evidence of dual directions of tectonic transport in the Piedmont Province, the same data that argue against the simpler one-stage model based only on Valley and Ridge data.