Abstract Post-Paleozoic tectonic activity in the Appalachian orogen (including the concealed basement of the passive margin) is primarily a consequence of the breakup of Pangaea and the opening of the Atlantic Ocean. It embraces a major tectonic cycle that is marked by Late Triassic-Early Jurassic rifting of the Alleghanian-Variscan orogen and by Middle Jurassic to Recent drifting of the newly forming passive margin.