A NEW BEDROCK GEOLOGIC MAP OF THE NORTH CAROLINA PORTION OF THE LANDRUM 1:24,000-SCALE QUADRANGLE

The North Carolina Geological Survey produced a new 1:24,000-scale bedrock geologic map of the North Carolina portion of the Landrum 7.5-minute quadrangle in Polk County, cooperatively funded through the STATEMAP component of the National Cooperative Geologic Mapping Program. Bedrock geology of the map area comprises components of the Tallulah Falls (TFF) and Poor Mountain Formations (PMF), unnamed meta-igneous rocks (UMIR), and granitoid gneiss (COgg).

Foliations and compositional layering are both complexly folded. Strike orientations vary but there is a well-defined NW-trending population. Dips are generally shallow and rarely greater than 45°. We identified a prominent, steeply-dipping joint set of azimuth 90-270°, and NE- and NW-trending brittle fault zones characterized by quartz breccias.

Neoproterozoic to Cambrian meta-sediments of the TFF are the oldest rocks here. The TFF rocks are upper amphibolite metamorphic facies and locally migmatitic.

UMIR consist chiefly of hornblende quartzo-feldspathic gneiss and hornblende gneiss. A minor altered ultramafic unit within the UMIR consists of an altered pyroxenite core surrounded by amphibolite. In many localities, porphyroclastic biotite gneiss separates metagraywackes and schists of the TFF from UMIR lithologies.

Previous workers have differing interpretations of UMIR equivalent lithologies. Conley and Drummond (1975) reported that UMIR rocks were intrusions although, more recently UMIR lithologies have been assigned to the amphibolite-rich lower TFF (Davis, 1994; Bream 1999). In our map area UMIR rocks occupy the same structural position as the lower TFF in adjoining quadrangles, but based on structural and textural evidence we favor the interpretation that they are intrusive into the TFF. The UMIR rocks here may represent a compositional variant of the Dysartsville Gneiss identified by Goldsmith and others (1988) and Bream (1999).

The PMF lies structurally above and in fault contact with the TFF and UMIR. Two units within the PMF were identified: 1) meta-sediments and amphibolite, undivided; and 2) quartzite/meta-arkose. PMF rocks are at sillimanite-grade conditions and are locally migmatitic. The fault separating the PMF and TFF is tentatively correlated with the Seneca fault.