Abstract

Following the Grenville orogeny, rocks across the Appalachians record deformation from the Ordovician Taconic, Silurian-Devonian Acadian, and the late Paleozoic Alleghanian orogenies. While there is an abundant record of Taconic and Alleghanian deformation in the Blue Ridge of the southern Appalachians, a record of the Acadian event is limited with the Burnsville shear zone representing the only record of deformation from this event. This shear zone was previously mapped south of the Grandfather Mountain Window from Burnsville, NC southwest towards Clyde, NC and records dextral transpression. This shear zone has been correlated to the Gossan Lead fault north of the Grandfather Mountain Window. While previous studies have constrained the timing of this shear zone near Burnsville, NC, the age of deformation toward its southernmost mapped extent near Clyde, NC has not been constrained. Dynamic recrystallization textures of quartz along with electron backscattered diffraction (EBSD) patterns from quartz [c] axes from samples collected within the shear zone in the Clyde quadrangle place constraints on the deformation temperatures. These constraints were combined with 40Ar/39Ar cooling ages from muscovite to bracket the timing of deformation. Quartz exhibits subgrain rotation recrystallization (SGR) with many portions of the shear zone overprinted by bulging recrystallization (BLG). Combined with opening angles of quartz [c] axis cross girdles, deformation occurred from temperatures of ~400-500° C and was overprinted at temperatures of ~390° C. These data combined with new ages and a muscovite closing temperature of ~400° C suggest that dextral transpression was ongoing in the Clyde quadrangle at ~350 Ma. This is markedly younger than previous constraints north near Burnsville where deformation occurred at >500° C between ~377 and 360 Ma.

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