A NEW 1:24,000-SCALE GEOLOGIC MAP 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 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 Dysartsville Complex (DC).

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

The DC is composed of complexly interlayered felsic and biotite gneisses with minor interlayers of other lithologies mentioned above in the TFF, and a hornblende gneiss of uncertain affinity. These felsic and biotite gneisses are interpreted to be related to the Dysartsville gneiss, a tonalite mapped north of the quadrangle with a U-Pb crystallization age of 468 ± 8 Ma (Bream 1999, 2003). On the Shingle Hollow quadrangle, contacts between the DC and TFF appear to be gradational. The DC may represent diatexite migmatite that originated through anatexis of the TFF or an intrusion into the TFF.

The PMF is subdivided into a metasandstone/quartzite/meta-arkose unit and an undivided unit consisting of interlayered amphibolite and meta-sediments. PMF rocks were metamorphosed to sillimanite-grade conditions and are locally migmatitic. The PMF is interpreted to be unconformably above the TFF and DC.

A thrust fault places the PMF/TFF/DC package structurally above the PMF, resulting in the TFF being in fault contact with the PMF in the NW corner. Generally, foliation planes strike NE with most dip values less than 35°. Although, at the outcrop scale foliation is complexly deformed through folding and migmatization. Steeply-dipping WSW- and SE-trending joint sets were identified. Whole rock geochemical analyses were performed for ten samples. Five stream sediment samples from relatively unmodified watersheds were analyzed to determine heavy mineral concentrations.