EVIDENCE FOR ITERATED ROTATION OF CONVERGENCE DIRECTIONS DURING ALLEGHANIAN DOCKING

Recent mapping around the Appalachian bend in central Pennsylvania has shown a sequence of contractional directions that is consistent with convergence directions in other areas of the Alleghanian-Ouachita-Variscan orogen. Based on this new data, it is now possible to reconstruct a sequence of rotating convergence vectors. These rotating convergence vectors appear to affect the entire orogen rather than acting as a “zipper” closure as previously proposed.

Initial convergence directions were north to slightly east of north (current orientation for the central Appalachians), creating the fold-and-thrust belts of the Marathon basin, the Ouachita-Black Warrior system, and the initial northern central Appalachian trend. The second convergence direction lay between 330˚ and 340˚ producing the main northern central Appalachian trend, including its extensions in New England and maritime Canada, and the main Variscan trend in Europe. The third convergence direction was approximately 310˚, producing the primary southern Appalachian trend and the Nittany Valley trend. The fourth, and apparently last, convergence direction was approximately 295˚, producing the main central Appalachian trend and the central Texas trend.

The convergence in the initial direction apparently continued for considerably longer than that for the later directions. The transitions to successive convergent directions appear to have been quite abrupt, with no intermediate shortening structures being produced along the foreland margin. This suggests that the docking occurred by iterated rotation of convergence directions rather than a gradual rotation of closure directions.