APPALACHIAN SUTURES

Sutures are faults that join tectonostratigraphic terranes (TT) to each other, continents to each other, and TT to continental landmasses. Sutures occur in all mountain chains, and in the roots of mountain chains exposed in shields. The numbers of sutures in a chain is determined by its accretionary history, numbers of TT, and the numbers of large and small oceans that closed during its history. The Cretaceous-Tertiary Alps of France, Switzerland, and Austria contain relatively few sutures, because they were formed by subduction of a relatively small amount of ocean crust and accretion of no arcs or other TT. In contrast, the Mesozoic-Tertiary North American Cordillera contains large numbers of sutures that bound TT or suture TT to the continent—without a future continent collider to end its constructional phase.

The Appalachians contain a moderate number of TT, and had an early accretionary history, but are the product of three major accretionary and collisional events, Taconian, Acadian/Neoacadian, and Alleghanian orogenies affecting the entire chain—recording a complete Wilson cycle from the Neoproterozoic breakup of Rodinia to the Permian amalgamation of Pangea. The Appalachians contain several major sutures traceable throughout the orogen: the Baie Vert-Brompton-Whitcomb Summit-Gossan Lead-Hayesville-Allatoona-Hollins line in the western crystalline core (Taconian), Red Indian-Central Piedmont suture (Acadian-Neoacadian), and the least-well known Africa-composite Laurentia suture. Suitably oriented, unfolded segments of these sutures were reactivated, like several other major faults (e.g., Norumbega, Brevard). The Central Piedmont suture, for example, formed during the mid-Paleozoic orogeny, but was reactivated during the Alleghanian with curved segments cut by Alleghanian faults. The Appalachian orogen is a composite orogen containing sutures related to the three major accretionary and collisional events that formed the orogen and amalgamated Pangea. Segments of Appalachian sutures also were zones of crustal weakness that became loci of Triassic-Jurassic normal and sinistral faulting prior to Pangea breakup.