A NEW 1:24,000-SCALE GEOLOGIC MAP OF THE SOUTHERN HALF OF THE PEA RIDGE 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 Pea Ridge 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 (TFF) and Poor Mountain Formations (PMF), unnamed meta-igneous rocks (UMIR), and granitoid gneiss (GG).

Foliations (compositional layering and schistosity) are generally parallel and complexly deformed. Foliation data define a weak NW strike-trend with most dip values less than 35 degrees. Steeply-dipping joint sets trending ENE and ESE were identified along with ENE-trending quartz breccias defining brittle fault zones likely associated with the Tryon-Marietta fault zone of Garihan and Ranson (1992).

Neoproterozoic to Cambrian TFF meta-sediments are the oldest rocks in the map area. The TFF consists of a porphyroblastic biotite gneiss unit and a structurally higher undivided metagraywacke, schistose metagraywacke, and mica schist unit. In some localities, the porphyroblastic biotite gneiss unit separates meta-sediments of the TFF from UMIR. The TFF has been metamorphosed at upper amphibolite facies and is locally migmatitic.

UMIR consist of hornblende quartzo-feldspathic gneiss, hornblende gneiss, amphibolite, and minor altered ultramafic bodies. Similar to the Landrum quadrangle directly SW, UMIR rocks in Pea Ridge are interpreted to be intrusive into the TFF based on structural and textural evidence, and 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 four units: 1) metasandstone/quartzite/meta-arkose; 2) schist; 3) amphibolite; and 4) an undivided heterogeneous unit consisting of interlayered PMF lithologies. PMF rocks were metamorphosed at sillimanite-grade conditions and are locally migmatitic.

Several small cross-cutting bodies of weakly foliated GG intrude the UMIR and TFF. GG is more resistant than the surrounding rocks and appears to be much less deformed.