GEOLOGY OF THE SOUTHERN HALF OF DACUSVILLE 7.5-MINUTE QUADRANGLE, PICKENS COUNTY, SOUTH CAROLINA

Geologic mapping at 1:24,000 scale has been completed in the southern half of Dacusville 7.5-minute quadrangle (DQ). The main regional structure there is the Seneca fault, which dips gently southeast and places rocks of the Six Mile thrust sheet over rocks of the Walhalla sheet. Hanging wall units primarily are dark, migmatitic, medium- to coarse-crystalline, schistose muscovite-biotite gneiss, and minor amphibolite, muscovite schist, sillimanite-muscovite schist, and metaquartzite. Footwall units include leucocratic, fine- to medium-crystalline, biotite quartzo-feldspathic gneiss, and a dark biotite, feldspar augen gneiss (BAGN). Locally a biotite, megacrystic feldspar gneiss (individual idioblastic feldspars 4-10 cm in long dimension) is present in the footwall. Both hanging wall and footwall units are intruded by poorly foliated granitoid gneiss.

The strike of the Seneca fault is ~N60°E. It crosses the entire quadrangle and localizes the Machine Creek drainage. Irregularities in its trace indicate the fault has been affected by post-Seneca folding. Cross sections show the Seneca fault in DQ is a shallow-dipping, folded thrust, and locally the allochthon is < 50-100 m thick. Several prominent windows southeast of the main Seneca fault trace lie along major south-flowing drainages, the result of both topographic effect and warping of the thrust.

Foliation attitudes in hanging wall rocks define a prominent, upright to inclined, gentle antiform (beta=33°/N76°E), the southwest continuation of the Stratford Forest antiform in Paris Mountain quadrangle. Stereoplots of footwall BAGN and non-BAGN lithologies indicate both units have undergone similar polyphase folding episodes. The prominent folds in footwall rocks at all scales are northwest-vergent, overturned, tight, chevron-style folds. The biotite granitoid gneiss is interpreted to post-date folding.

Our mapping in DQ indicates the Mesozoic Easley dolerite dike (Snipes and Furr, 1979) is a set of 3-4 dikes (2-4 km long) trending N25°-40°W. The dikes are undeflected as they cross the Seneca fault trace. Two or three poorly exposed zones of siliceous cataclasite and microbreccia strike ~N70°E, transecting foliation in footwall gneiss. The most prominent zone (1.4 km long) lies along the Wolf Creek drainage.