Appalachian carboniferous dextral strike‐slip faults: An example from Brookneal, Virginia

Abstract

The northern Appalachian, dextral fault system of late Paleozoic age is also present in the central and southern Appalachians. An example of a dextral strike‐slip fault is the 4 km wide Brookneal shear zone in the southwest Virginia Piedmont. The shear zone is, in part, superimposed on the Melrose Granite where an S‐C mylonite was produced by dynamic recrystallization of all constituent minerals. The Arvonia metasedimentary and Charlotte belt metavolcanic rocks contain spaced dextral shear bands at a consistent +24° ± 3° to the shear zone boundary. A minimum displacement estimate of 17 km was obtained from rotated foliation measurements in the Melrose Granite. The age of movement on the Brookneal shear zone has been constrained by isotopic dating to between 324 and 300 Ma. Other faults in the southern Appalachians, including the Nutbush Creek and Modoc zones show similar ages and relative offsets. Possible plate tectonic models that could account for the late Paleozoic dextral fault system throughout the Appalachians include: (1) tectonic escape resulting from the collision of a plate with North America to the north of the Canadian Appalachians, (2) postcollision interplate readjustments involving counterclockwise rotation of Africa relative to North America, and (3) oblique convergence of eastern North America with an oceanic plate moving west.