A NEW 1:24,000-SCALE GEOLOGIC MAP OF THE SOUTHERN HALF OF THE SHINGLE HOLLOW 7.5-MINUTE QUADRANGLE, RUTHERFORD AND POLK COUNTIES, NORTH CAROLINA

The North Carolina Geological Survey has produced a new 1:24,000-scale bedrock geologic map of the southern half of the Shingle Hollow 7.5-minute quadrangle in Polk and Rutherford Counties, cooperatively funded through the STATEMAP component of the National Cooperative Geologic Mapping Program. Bedrock geology of the map area comprises the Tallulah Falls Formation (TFF), Poor Mountain Formation (PMF), and unnamed meta-igneous rocks (UMIR).

Neoproterozoic to Cambrian TFF meta-sediments are the oldest rocks in the map area. The TFF in the study area consists of a biotite gneiss unit with minor metagraywacke, schistose metagraywacke, mica schist, felsic gneiss, and hornblende-biotite gneiss. The TFF has been metamorphosed to upper amphibolite facies and is locally migmatitic.

UMIR consist of mainly quartzo-feldspathic gneiss with minor hornblende quartzo-feldspathic gneiss, hornblende gneiss, and amphibolite. Based on structural and textural evidence, UMIR rocks are interpreted to intrude only the TFF and not the PMF. UMIR rocks may be related to the Dysartsville Gneiss (Goldsmith and others, 1988; Bream, 1999).

The PMF lies structurally above and in fault contact with the TFF and UMIR. The PMF is subdivided into a metasandstone/quartzite/meta-arkose unit and an undivided heterogeneous unit consisting of interlayered metagraywacke, schist, calc-silicate, and amphibolite. PMF rocks were metamorphosed to sillimanite-grade conditions and are locally migmatitic.

Foliations (compositional layering and schistosity) are generally parallel and complexly deformed. Foliation data define a weak NE strike-trend with most dip values less than 35 degrees. Steeply-dipping WSW- and ESE-trending joint sets were identified. Whole rock geochemical analyses (57 elements) were performed for ten representative samples. Five stream sediment samples from relatively unmodified watersheds were analyzed to determine heavy mineral concentrations.