SOUTHERN APPALACHIAN HINTERLAND FREEWAY SYSTEM BEFORE THE I-85 AND I-95 CORRIDORS: THE EASTERN PIEDMONT FAULT SYSTEM AND LITHOTECTONIC TERRANES IN NORTH CAROLINA

The southern Appalachian hinterland in the NC eastern Piedmont (NCEP) contains an array of terranes that have unclear lithotectonic domain affinity. Historically, four greenschist facies (chlorite-biotite to local staurolite zone) suprastructural and five amphibolite facies (garnet-staurolite-kyanite-sillimanite zone) infrastructural terranes have been interpreted to be parts of Carolinia and Goochland. At least seven strike-slip strands of the late Paleozoic Eastern Piedmont fault system (EPFS) and two late Paleozoic to early Mesozoic normal faults link as a complex ductile-brittle network that juxtapose the terranes. Recent mapping and geochronological studies allow us to propose new hypotheses for the origin of structures and tectonic evolution of these terranes.

The NCEP lies northeast of an EPFS strike change from N40-50E to N-S-N15-20E between SC and VA. This strike change is interpreted as a restraining bend leading to a transpressive strain regime, joining of ductile dextral strands as strike-slip duplex and half-flower structures, metamorphism of igneous and sedimentary protoliths, and granite plutonism. Crystal-plastic shear zone evolution may involve zippered strike-slip then rotational Laurentian–Gondwanan collision during Pangea amalgamation while crystal-plastic-brittle normal faults mark its breakup. All conjugate dextral EPFS strands among suprastructural and infrastructural terranes form Y- and l-type shear zone junctions and internal infrastructural strain yield dextral kinematic indicators for the strands. Zippered shear zone junctions require a combination of dextral and sinistral kinematics; however, data supporting sinistral-slip have not been reported. EPFS strands in the NCEP instead appear to merge as an orogen-scale dextral freeway system that modeling indicates can produce significant displacement. An east-side-south freeway may explain U-Pb zircon geochronology indicating Early Devonian magmatic and sedimentary protoliths in NCEP infrastructural terranes east of Carolinia and Goochland and supports a far traveled origin. Geochronology and thermochronology also show that high-grade metamorphism occurred by the earliest Alleghanian while post-orogenic ductile-brittle uplift of the freeway was active by latest Permian to early Triassic time.