AVALONIAN/CAROLINA TERRANE EXOTIC CRYSTALLINE ROCK HORSES ALONG THE ALLEGHANIAN BREVARD FAULT IN SOUTH CAROLINA: INSIGHT INTO LATE PALEOZOIC BREVARD FAULT KINEMATICS AND DISPLACEMENT

Two crystalline rock horses located along the SE margin of the Alleghanian dextral Brevard fault zone (Bfz) in NW SC have been known for several decades. These horses occur along a suite of faults that cuts klippen of the SW-directed Inner Piedmont Neoacadian Alto (Six Mile) allochthon. New SHRIMP and LA-ICPMS U-Pb zircon age dates from the metasedimentary (Q-M-chlorite-Pl-calcite mylonite) component of the larger horse yield ages common to the Avalon/Carolina superterrane, exotic to well-known Laurentian assemblages on both sides of the Bfz. The detrital zircon suite in the metasedimentary unit is dominated by 500 and 600 Ma zircons, a second largest population from 1300 to 2000 Ma, and essentially no Grenvillian component. The granitoid component (microcline-Pl-Q-Mu-Bi-gar mylonite) has an age of 432 + 4.8 Ma, suggesting possible derivation from the 430 Ma plutonic suite in northern VA and MD—a prominent component of the Cat Square terrane detrital zircon suite in the Carolinas.

The nearest exposed Avalonian/Carolina superterrane rocks are >150 km to the NE, but nowhere contact the Bfz at present erosion level. While these horses may have originated several hundred km farther NE in the central Appalachians, a plausible explanation for their derivation could be that they are remnants of Avalonian/Carolina terrane rocks that once formed the western part of the upper plate/tectonic lid of the SW-directed Neoacadian-early Alleghanian (Late Devonan-Mississippian) orogenic channel during accretion of Avalon/Carolina. This oblique subduction is responsible for producing the bimodal Late Devonian-Mississippian plutonic suite in the overriding Carolina superterrane upper plate. Today the eroded fossil subduction zone survives as the central Piedmont suture. Carolina/Avalon would have once covered the Inner Piedmont (and easternmost Blue Ridge) to depths of ~20 km, and has since been eroded. These data provide additional insight into the complex history of the Bfz and Piedmont.