THE BREVARD FAULT: PALEOZOIC MULTIPLE REACTIVATION BELOW AND ABOVE THE DUCTILE-BRITTLE TRANSITION, AND KINEMATIC INSIGHTS FROM FAR-TRAVELED HORSES

The Brevard fault zone (Bfz) is one of the largest faults in the Appalachians, extending from Alabama to Virginia. Although it is not a suture, it had a very complex history of Paleozoic movement and reactivation: (1) 403–345 Ma Acadian-Neoacadian (AN), accompanying the middle-upper amphibolite facies thermal and deformation peak and dextral, SW-directed emplacement of the Inner Piedmont (IP); (2) dextral ~280 Ma lower-greenschist facies ductile early Alleghanian reactivation; and (3) ~260 Ma late Alleghanian brittle dip-slip reactivation. The Bfz is comparable to large faults with polyphase movement in other orogens, e.g., the Periadriatic line in the Alps. Two types of far-traveled, fault-bounded horses have been identified in the Bfz: (1) metasedimentary-granitoid (MG) horses along the southeastern margin of the retrogressive Bfz in NC and SC; and (2) limestone/dolostone horses along the brittle, ~260? Ma Rosman thrust—the contact between Blue Ridge and Brevard fault zone. Field, stratigraphic, petrographic, and Sr-isotope data suggest the carbonate horses are derived from Valley and Ridge carbonates beneath the Blue Ridge–Piedmont megathrust sheet. MG rocks horses occur along faults that cut klippen of the southwest-directed IP, and AN Alto-Six Mile allochthon. LA-ICP-MS U-Pb zircon analyses of metasedimentary mylonite yield dominant 600 and 500 Ma and 2100 to 1300 Ma detrital zircon suites, with rare 1 Ga zircons, with peri-Gondwanan (PG) provenance. PG Neoproterozoic to Cambrian Avalon–Carolina superterrane (AvC) rocks are nowhere in contact with the Brevard fault zone at present erosion level. These far-traveled MG horses could be remnants of AvC rocks that once formed the tectonic lid of the southwest-directed Neoacadian–early Alleghanian (Late Devonian–early Mississippian) orogenic channel formed during north-to-south zippered accretion of AvC. The remnant fossil subduction zone survives as the central Piedmont suture. AvC rocks would have once covered the IP (and easternmost Blue Ridge) to depths of >20 km, and were since eroded. Data from these two suites of horses of markedly different colors provide insights into the mid- to late Paleozoic history and kinematics of the Bfz, IP, and AvC.