LOCATION: The outcrops are located on Cedar Shoals Creek near where it meets the Enoree River 0.1 mile past the Horseshoe Falls bridge over Cedar Shoals Creek. Horseshoe Falls Road intersects SC 56 1.0 mile north of the bridge over the Enoree River. These outcrops are owned by the South Carolina State Park System. (Fig. 18, Philson Crossroads quadrangle)
DESCRIPTION: These outcrops are the type locality for the Cedar Shoals gneiss of Horkowitz (1984). The Cedar Shoals gneiss comprises quartzo-feldspathic biotite paragneiss and felsic orthogneiss (Horkowitz, 1984). Metamorphic minerals present include sillimanite, muscovite, and garnet. Amphibolite boudins and pods are recognized in the Cedar Shoals gneiss, as well as dismembered metaplutonic rocks with compositions from tonalite to gabbro, and pegmatitic and aplitic dikes. These outcrops are comparable to Inner Piedmont outcrops along the central Piedmont suture on Fairforest Creek in the Glenn Springs quad described by Dennis (1988, stop 9, p. 245).
The slabby appearance, northeasterly strikes, gentle dips (typically 20-40deg.) to the southeast observed here are typical of the easternmost Inner Piedmont in northwestern South Carolina. Some small folds may be observed the axes of which plunge to the south at 15-20deg.. These parallel asymmetric, northwest-vergent mesoscopic folds, mineral lineations, and intersection lineations in the Carolina terrane (Dennis, 1988, 1995). Because foliations are folded without interruption across the central Piedmont suture (i.e. formlines are continuous across the terrane boundary) defining great circles with poles that also plunge 15-20deg. to the south (Dennis, 1988, 1995), and the lineation is a fabric element with a consistent geometry on either side of the terrane boundary, these folds are interpreted to postdate major motion on the central Piedmont suture and be Alleghanian in age.
From this location, Dallmeyer and others (1986) report a 40Ar/39Ar plateau age for biotite at 259+/-5 Ma (their sample 47). This sample and two other Inner Piedmont biotite plateaux from northwest of here in the Enoree quad (their samples 48 and 49) with ages of 272+/-5 and 271+/-5 Ma led these authors to conclude that the Inner Piedmont in this area cooled through 300deg.C ca. 260-270 Ma.
Horkowitz (1984) interpreted that the protoliths of the Cedar Shoals gneiss included graywacke, arenaceous sediments and siliceous/felsic volcanic rocks based on five petrographic modal analyses and plotting his modal data on a QFM diagram.
Structurally these rocks at Cedar Shoals are separated from the central Piedmont suture (as mapped by Horkowitz, 1984) and beneath a ~ 3 km width of biotite gneiss that also includes marbles, calc-silicates, sillimanite-muscovite schist, and garnet-quartzites (Horkowitz, 1984). Horkowitz' (1984) lithologic descriptions for this biotite gneiss unit are reminiscent of the southernmost exposures of Battleground Formation in the Glenn Springs and Pacolet quads (Dennis, 1988, especially p. 231, 246; 1989; Mittwede, 1988, especially p. 253-256). Horkowitz' (1984) biotite gneiss unit may be primarily highly altered metavolcanic rocks of the Carolina terrane and lie east of the central Piedmont suture. If this correlation is true, then the central Piedmont suture lies less than 1 km (across strike) southeast of this site.