4 Structural Geology and Tectonics (Posters)

Thursday, 5 April 2001
8:00 AM - 12:00 PM

GEOLOGIC TRANSECT ACROSS THE TABLE ROCK AND EASTATOE GAP 7.5-MINUTE QUADRANGLES, WESTERN INNER PIEDMONT, GREENVILLE AND PICKENS COUNTIES, SC-NC

Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

A complete northwest to southeast geologic transect from the Brevard fault zone to the Seneca (Sugarloaf Mountain) fault, which floors the Six Mile thrust sheet, is encompassed by the Eastatoe Gap and the Table Rock 7.5-minute quadrangles. Mylonitic Henderson Gneiss (Hgn), structurally above the Brevard fault, displays well-developed shear sense indicators, strain partitioning, and decreasing intensity of deformation southeastward from the Brevard fault. Hgn is separated from an overlying sill-like body of polyphase deformed Table Rock Suite biotite gneiss (TRgn) along a sharp regional contact (intrusive? thrust?) dipping gently-moderately southeast. Two zones of ductile-deformed Poor Mountain amphibolite, biotite gneiss, and garnet schist units, each bound above and below by regionally persistent thrust faults, transect the regional Hgn - TRgn contact at a shallower angle. The two zones (thrust duplicated from one zone) are each 0.2 - 1.5 km wide, exceeding 80 km in strike length. Hgn, the ductile-deformed Poor Mountain units, and a sliver of TRgn are considered here structures of the Stumphouse Mountain nappe (Hatcher, 1999), extending an unknown distance northward into the Brevard, NC quadrangle.

The Walhalla nappe contains TRgn, with complexly interlayered and sheared, discontinuous Poor Mountain amphibolite, garnet schist, metaquartzite, metagabbro, and ultramafic schist units of northeast strike. Previous misinterpretation of the Seneca fault as intricately and repeatedly infolded within rocks of the main body of the Walhalla nappe is herein modified. The Walhalla nappe, a belt ~8 km wide, is footwall to the Six Mile thrust sheet, which contains Poor Mountain and Tallulah Falls formation rocks. Erosional outliers of Poor Mountain rocks above the multiply folded Seneca fault cap the highest quadrangle elevations (3000 - 3300 ft), at Table Rock, Pinnacle, Battered Rock, and Cold Branch mountains, The Stool, and at Caesars Head. Projections from these elevations to the regional trace of the Seneca fault indicate the fault dips ~6° southeast. Brittle faults define an easterly graben of the Marietta-Tyron fault system dissecting Walhalla nappe and Six Mile sheet rocks.