KINEMATICS AND DEFORMATION CONDITIONS OF THE GOSSAN-LEAD AND FRIES FAULTS, NORTHWESTERN NORTH CAROLINA

Geologic mapping, and kinematic, and microstructural analysis along the Fries and Gossan-Lead faults, located within the Blue Ridge province of northwestern North Carolina, provide evidence for dominantly top-to-the-NW thrusting at upper greenschist-lower amphibolite-facies conditions. The Gossan-Lead fault separates rocks of the Ashe Metamorphic Suite from basement gneisses, and is characterized by a wide mylonitic zone that extends into both the hanging wall and the footwall. The Fries Fault is located entirely within the basement and appears to be a less discrete zone of mylonitization with diverse rock types and heterogeneous strain intensity. Kinematic indicators consistent with top-to-the-NW thrusting include: SE-plunging mineral lineations, S-C, C-C’, and oblique quartz fabrics, mica fish, and tails on feldspar augen and garnet porphyroblasts. However, locally developed asymmetric folds and crenulations with an orthogonal orientation may suggest these faults record multiple phases of motion. Quartz grains are strongly dynamically recrystallized with evidence for widespread bulging grain boundary migration and subgrain rotation recrystallization, suggesting conditions may be as high as lower amphibolite-facies. In most thin sections feldspar has few subgrains and is not dynamically recrystallized but a few samples provide evidence for incipient development of bulging grain boundary migration, which is consistent with lower amphibolite-facies deformation. Additionally, a lack of biotite retrogression to chlorite provides further support for metamorphism at higher temperatures than most Southern Appalachian Alleghanian-aged faults.