A NEW BEDROCK GEOLOGIC MAP OF THE BREVARD QUADRANGLE, TRANSYLVANIA COUNTY NC AND GREENVILLE COUNTY, SC

The North Carolina Geological Survey, in conjunction with the United States Geological Survey STATEMAP program, has produced a new 1:24,000-scale bedrock geologic map of the Brevard 7.5-minute quadrangle in Transylvania County, NC and Greenville County, SC. Bedrock geology of the Brevard quadrangle comprises components of the Ashe Metamorphic Suite-Tallulah Falls Formation (AMS-TFF), Brevard Zone (BZ), Chauga River Formation (CRF), Henderson Gneiss (HG) and Table Rock plutonic suite (TR).

Foliation and mylonitic foliation generally strike NE and dip SE. Dip values decrease markedly in rocks SE of the BZ. A prominent, steeply-dipping fracture set of azimuth 315°-135° along with a subordinate fracture set of azimuth 225°-45° were identified from joint data. Both linear and planar fabric orientations are similar to those mapped in the Horse Shoe quadrangle to the NE.

Neoproterozoic to Cambrian metasediments of the AMS-TFF underlie the northwestern corner of the quadrangle, and are the oldest rocks in the map area. AMS-TFF rocks have been metamorphosed to upper amphibolite facies and are locally migmatitic.

SE and structurally above the AMS-TFF in fault contact are BZ rocks consisting mainly of greenschist-facies sericite/graphitic phyllite and mylonitic granitic gneiss/phyllonite. The protolith of much of the mylonitic granitic gneiss/phyllonite is interpreted to be HG.

SE and structurally above the BZ in fault contact is a large volume of lineated HG. We identified three subdivisions within the HG based on composition, grain size and degree of deformation.

A thin panel of CRF metasediments concordant with the regional foliation was identified in the central portion of the map. We interpret it to be the continuation of the Eastatoe fault block mapped on the Standingstone Mountain quadrangle by Garihan and Ranson (2007). NW and SE of this panel, isolated bodies of TR granitoid gneiss are present within the HG. Due to the presence of these bodies and the diffuse contact between the main bodies of the HG and TR, we suggest that the TR is in intrusive contact with the HG in this area.

The SE portion of the map is dominated by TR granitic gneiss with the exception of a thin klippe of the Poor Mountain Formation in thrust contact with the TR.