AN ALLEGHANIAN (?) BRITTLE THRUST AND ASSOCIATED HINTERLAND-DIRECTED BACK-THRUST SYSTEM IN THE WESTERN INNER PIEDMONT OF SOUTH CAROLINA AND ADJACENT NORTH CAROLINA

An unnamed, NW-directed brittle thrust, interpreted to be Alleghanian age, has been traced across Table Rock, Brevard*, Standingstone Mountain, and Horse Shoe* quadrangles in the western Inner Piedmont (IP) of South Carolina and adjacent North Carolina. The fault bounds the SE margin of a narrow outcrop belt of Chauga River Formation (CRF) rocks along its NE-strike length. At Dismal Creek in Standingstone Mountain quadrangle, a splay of this thrust near its leading edge has displaced the older, early-mid Paleozoic Eastatoee ductile thrust (ie. duplicated the footwall Henderson Gneiss-CRF thrust contact). The Slicking Gap normal fault, dipping 25°-30° SE at the surface, approximately parallels the adjacent Alleghanian thrust and lies 1-3 km SE of its surface trace.

Regionally Six Mile thrust sheet rocks lie structurally above Walhalla thrust sheet rocks in the IP. However, associated with the NW-directed Alleghanian thrusting, Walhalla thrust sheet gneisses were back-thrust toward the hinterland over the Six Mile thrust sheet rocks, to the SW, S, and SE. This system of brittle back-thrusts is present in Table Rock, Cleveland, Standingstone Mountain, Zirconia, and Slater quadrangles. Some back-thrusts appear to be localized along or near older greenschist-grade ductile muscovite-quartz shear zone schists and strain-softened zones in Table Rock gneiss produced by earlier gravitational collapse of the IP thrust stack. Back-thrusting deformed Six Mile and Walhalla thrust sheet rocks and locally folded and truncated these older, collapse-related ductile shear zones.

The Slicking Gap normal fault may be related to hanging wall extensional stresses associated with hinterland-directed back-thrusting. Alternately, the normal fault developed, or was reactivated, during later regional Mesozoic SE-ward extension. The Slicking Gap fault is interpreted to be listric and to reactivate the older Alleghanian thrust surface at depth.

*based on NC Geological Survey mapping