GEOLOGY OF THE STANDINGSTONE MOUNTAIN 7.5-MINUTE QUADRANGLE, INNER PIEDMONT, NC-SC

Four major Paleozoic thrust packages in Standingstone Mountain quadrangle involve metamorphic units of the Poor Mountain and Tallulah Falls formations, Table Rock gneiss and augen gneiss, and the Henderson Gneiss. A northeast belt of Henderson Gneiss (>5 km wide), the structurally lowest sheet, is transected by a continuous, easterly sheet (0.2 - 0.8 km wide) of resistant, ductilely deformed schist (sheet 2). Southeast-dipping thrusts bound the upper and lower margins of the transecting schist zone; they are not folded and may represent imbricate splays above a single detachment. The schist is correlative to the Brevard-Poor Mountain Transition Member of the Poor Mountain Formation (Hatcher and Acker, 1984, MS-26, SC Geological Survey). Although present in Table Rock quadrangle, Poor Mountain amphibolite is largely absent in sheet 2. Resistant Table Rock gneiss of the Walhalla nappe (sheet 3) is placed over Henderson Gneiss along a sharp regional thrust. North-northwest trending tear faults displace this thrust locally. A gneiss-augen gneiss contact within the Table Rock unit defines a northwest-vergent, overturned antiform in the southern part of the map area. Schist, gneiss, amphibolite, and metaquartzite of the Poor Mountain and Tallulah Falls formations in the Six Mile thrust sheet (sheet 4) overlie the Table Rock gneiss along the Seneca fault. Subsequent to emplacement, the Seneca fault surface was deformed along northeast and northwest folding trends. Significant thrusting, with related folding, which post-dates movement along the Seneca fault, is represented by planar faults and shear zones. They occur as: 1) previously unrecognized thrusts placing Table Rock gneiss westward over Six Mile thrust sheet rocks (locally developed); and 2) mylonitic zones up to several kilometers long within Table Rock gneiss.

Small horsts and grabens mark the southwest termination of the Mesozoic Gap Creek brittle normal fault. They break up the trace of the Seneca fault in the southeast part of the quadrangle.