STRUCTURE AND STRATIGRAPHY ACROSS THE REEDY RIVER THRUST FAULT, INNER PIEDMONT OF SOUTH CAROLINA

The boundary between the high-grade Inner Piedmont core and the medium-grade southeast flank was delineated across South Carolina by Overstreet and Bell in 1965. Griffin, 1971 and 1978, interpreted this boundary as a tectonic slide separating two northwest-verging nappes. In 1998, Nelson and others mapped the same contact in Greenville and Spartanburg counties as an unnamed thrust fault at the base of their Laurens thrust sheet (LTS).

That fault, herein the Reedy River thrust fault (RRTF), has been traced by detailed mapping for 50 miles (81 km) from Fork Shoals in southern Greenville County northeastward to Thicketty in western Cherokee County. Massive granite with minor biotite gneiss and sporadic amphibolite characterize the LTS from Fork Shoals to Reidville, southwest of Spartanburg. Near Reidville the granite is in contact with a thick, layered sequence of fine - to coarse-crystalline biotite gneiss that extends to Thicketty.

Three separate marker horizons help define the biotite gneiss stratigraphy. In structural order they are: 1) quartzite associated with garnet mica schist, 2) mica schist interlayered with amphibolite, and 3) rocks of the Hammet Grove ultramafic suite. The three horizons also define a large, open, northeast-plunging, overturned antiform, and the northwest limb of that fold is truncated by the RRTF.

Northwest of the RRTF, interlayered sillimanite-mica schist, biotite gneiss, and minor amphibolite compose the footwall rocks of the Six Mile thrust sheet. This layered package extends unbroken from Fork Shoals to Thicketty. In particular, recent work in the Greer-Taylors area of Greenville County shows no evidence for a thrust fault inferred by Nelson and others to separate the Paris Mountain and Six Mile thrust sheets. These relations suggest 1) the Six Mile thrust sheet underlies the RRTF from Fork Shoals to Thicketty, and 2) the Paris Mountain thrust sheet is more restricted than previously mapped or does not exist.