THE COX CREEK FAULT AND ITS RELATIONSHIP TO THE BURNSVILLE FAULT, BLUE RIDGE THRUST COMPLEX, WESTERN NORTH CAROLINA

The Burnsville fault is a Devonian amphibolite-facies dextral strike-slip shear zone that separates the eastern and western Blue Ridge of western North Carolina. The Burnsville fault lies within the Fries thrust sheet, the structurally highest thrust sheet in the Blue Ridge thrust complex. Previous work has noted a structure between the Fries fault and the Burnsville fault, the Cox Creek fault, which separates two Grenville basement units of differing Paleozoic metamorphic grade. McHugh et al. (2009) reported that the Cox Creek fault is a southeast-dipping amphibolite-facies shear zone characterized by top-to-northwest sense of shear, based on analyses of outcrops near the branch line between the Fries and Cox Creek faults. These authors suggested two hypotheses for the origin of the Cox Creek fault: 1) the Cox Creek fault formed during transpression associated with movement along the Burnsville fault, or 2) the Cox Creek fault is a high-grade Alleghanian thrust fault. This purpose of this study was to investigate the extent of the Cox Creek fault in the Mars Hill, NC and adjacent quadrangles and to evaluate the hypotheses of McHugh et al. (2009). Within the study area, the Cox Creek fault lies 3 to 5 km northwest of the Burnsville fault. The Cox Creek fault is characterized by shallow to moderately plunging, northeast-southwest mineral elongation lineations and a well developed foliation that dips steeply southeast. Oriented thin sections from the Cox Creek shear zone show dextral oblique sense of shear. The recrystallization of plagioclase and K-feldspar, occurrence of myrmekite along K-feldspar grain boundaries, and mineral assemblages observed suggest deformation at amphibolite-facies conditions. The similarity in conditions of deformation in the Cox Creek and Burnsville faults and the presence of dextral kinematics in both faults supports the hypothesis that the Cox Creek fault may be associated with dextral movement along the Burnsville fault.