A NEW GEOLOGIC MAP OF THE OTEEN QUADRANGLE, BUNCOMBE COUNTY, NC

The North Carolina Geological Survey, in conjunction with the United States Geological Survey STATEMAP program, has produced a 1:24,000-scale bedrock geologic map of the Oteen 7.5-minute quadrangle in Buncombe County, NC. Bedrock geology of the Oteen quadrangle is comprised of the Ashe Metamorphic Suite-Tallulah Falls Formation (AMS-TFF), Alligator Back Metamorphic Suite (ABMS), and Brevard Zone (BZ) lithologies.

Non-mylonitic foliations are folded, generally strike NE-SW and dip SE and NW. Mineral lineations and fold axes are generally subhorizontal and trend NE-SW. Mylonitic foliations occur almost exclusively in the Brevard Zone and predominantly strike NE and dip SE. A prominent, steeply-dipping fracture set of azimuth 130°-310° was identified which parallels regional lineaments and is found on the adjoining Black Mountain and Craggy Pinnacle quadrangles.

Neoproterozoic to Cambrian metasediments of the AMS-TFF, the oldest rocks in the area, underlie the northwestern and central portions of the map. Mapped AMS-TFF units include metaconglomerate, metagraywacke, schistose metagraywacke, garnet mica schist, sillimanite schist, amphibolite, and altered ultramafic bodies. They have been metamorphosed to upper amphibolite facies and are locally migmatitic. Too small to be mapped at 1:24,000-scale, trondhjemites occur within the AMS-TFF as cross-cutting dikes and sills ranging in thickness from centimeters to meters.

Structurally above the AMS-TFF to the southeast is the ABMS consisting mainly of phyllite, metasiltstone, metagraywacke, metasandstone, and minor calc-silicate. The contact between the AMS-TFF and ABMS is placed at the first appearance of graphitic schist and is interpreted to be a tectonized unconformity. In contrast to the AMS-TFF, ABMS rocks in the map area are rarely migmatitic.

Structurally above the ABMS to the southeast are BZ units including sericite phyllite, garnet sericite schist, mylonitic metasandstone, siliceous marble, and mylonite. Bodies of mylonitic granitic gneiss within the BZ are interpreted to be fault slices of Henderson granitic gneiss. Rocks within and in close proximity to the BZ contain retrograde greenschist facies assemblages.