FIELD AND THERMOCHRONOMETRIC CONSTRAINTS ON MOTION ALONG THE FRIES AND GOSSAN LEAD FAULTS, NEAR BOONE NC

The Eastern Blue Ridge in the Appalachian Mountains spans from Alabama to Virginia. The Gossan Lead fault marks the edge of the Eastern Blue Ridge in western North Carolina; immediately north of the Grandfather Mountain Window this boundary is complicated by the presence of the Fries fault. These faults have been previously mapped, however, their exact locations and the nature of their intersection is unknown. Moreover, the timing and kinematics of faulting is not well determined, making it difficult to ascertain the tectonic affinity of these structures. We carried out extensive geologic mapping in the Boone quadrangle, determining the kinematics of the faults, and collecting samples for ⁴⁰Ar/³⁹Ar thermochronologic analysis in hornblende and muscovite. The northernmost area in the quadrangle is dominated by the Ashe Metamorphic Suite, which contains amphibolites and mica schists. This unit is separated from the amphibolites of the Pumpkin Patch Formation to the south by the northeast-dipping Gossan Lead fault. South of the Pumpkin Patch Formation is the feldspathic Cranberry Gneiss; the two are separated by the north-dipping Fries fault. The southern contact of the Cranberry Gneiss is marked by the Linville Falls fault, which separates the Blue Ridge rocks from the metaconglomerates and metasiltstones of the Grandfather Mountain Formation. Throughout the field area foliation generally strikes to the northwest and dips moderately to the northeast. Increased strain along the contacts provides evidence for faulting in these areas, and a majority of the shear sense indicators are consistent with thrust faulting. A hornblende ⁴⁰Ar/³⁹Ar age from within the Ashe Metamorphic Suite is consistent with cooling at ~340 Ma. Our field observations and results from hornblende ⁴⁰Ar/³⁹Ar thermochronology show that these faults were likely active as thrust faults during late Neo-Acadian to pre-Alleghenian time.