PALINSPASTIC RESTORATION OF THE SOUTHERN APPALACHIAN INNER PIEDMONT: LINKS BETWEEN THE ACADIAN CLASTIC WEDGE AND HIGH–TEMPERATURE DEFORMATION IN THE CRYSTALLINE CORE OF THE SOUTHERN APPALACHIANS

Geochronologic data document a major Neoacadian (360–340 Ma) tectonothermal event in the southern Appalachian Inner Piedmont (IP), but evidence of this event is not well supported in the southern Appalachian foreland. Palinspastic restoration of the IP from displacement estimates on the Brevard fault zone (BFZ) creates a kinematic model consistent with the location and SW time-transgressive migration of the Acadian clastic wedge in the foreland basin.

The IP is a composite amphibolite grade terrane that extends from VA to AL, reaching sillimanite I and II across its broad core. It is bound to the west by the BFZ and separated from the Carolina superterrane (Ct) to the east by the central Piedmont suture. The BFZ is a 15 to 20 km-wide amphibolite grade shear zone characterized by NE–SW-trending, moderately SE-dipping mylonitic foliations and subhorizontal NE–SW-trending mineral stretching lineations. The complex history of the BFZ involves (1) Neoacadian (Late Dev. to Miss.) high-temperature dextral strike-slip; (2) early Alleghanian (Miss.) greenschist grade dextral strike-slip, and; (3) late Alleghanian (Per.) brittle thrusting. Estimates of SW-directed displacement of the Neoacadian BFZ include minimal 200 km (retrodeformed shape of the Henderson Gneiss) to 400 km (shear zone width). Alleghanian phases account for an additional 50 km of SW–directed displacement associated with the 4 to 6 km-wide early Alleghanian fault zone and 10 km of later NW-directed thrust displacement. Displacements related to the two episodes of BFZ dextral strike–slip motion restore the IP a minimum 250 km to the NE near the Virginia Promontory by the Early Dev. Combining IP Neoacadian deformation, its palinspastic position, and SW migrating Acadian clastic wedge, we propose the following. Early to Mid Dev. oblique NNW-directed collision of the Ct with the eastern Laurentian margin near the New York promontory. Deformation progressed from N to S; the IP and western Tugaloo terrane were subducted beneath the Ct by ~380 Ma initiating partial melting, intrusion of anatectic granitoids, and SW–directed flow along the Neoacadian BFZ. Deposition in the foreland migrated southward to the Virginia Promontory by the Late Dev. and into TN by mid. Miss. Collision of Africa reactivated the BFZ and transported the IP and Ct to their final positions.