STRUCTURAL DEVELOPMENT ALONG THE WESTERN FLANK OF THE EASTERN PIEDMONT IN NORTH CAROLINA

The North Carolina eastern Piedmont exposes an array of metamorphic, igneous, and sedimentary relationships. Its rocks and ductile-brittle faults range from Neoproterozoic to early Mesozoic in age. They record the 1) magmatic and volcaniclastic evolution of a peri-Gondwanan island-arc, the Carolina Zone; 2) intra-arc tectonism during ~560 Ma Virgilina deformation; 3) accretion to eastern Laurentia in the middle Paleozoic Taconic/Cherokee orogeny; 4) Laurentian-Gondwanan continental convergence and Pangean supercontinent construction in the late Paleozoic Alleghanian orogeny; and 5) Mesozoic continental breakup during the rift-drift opening of the Atlantic Ocean.

During Pennsylvanian-Permian Alleghanian orogenesis, ductile strike-slip deformation overprinted the eastern Piedmont. Dextral transpression formed the Eastern Piedmont fault system, an anastomosing network of northeast-striking fault zones. They partition the first-order Carolina Zone into at least eight second-order tectonostratigraphic terranes having greenschist facies suprastructural or amphibolite facies infrastructural mineral assemblages and fabric elements. On the western flank of the eastern Piedmont, fault strands anastomose through island-arc rocks of several terranes, forming a 1-10 km-wide zone, the Nutbush Creek-Lake Gordon fault system (NCLG). The principal structure of the orogenic fault network, the NCLG extends at least 200 km from the Virginia state line to south-central North Carolina. Permo-Triassic ductile-brittle normal faults, nonconformable Late Triassic clastic sedimentary rocks and Jurassic diabase dikes record Mesozoic rifting and Pangean supercontinent breakup. The Jonesboro and Fishing Creek normal faults truncate the western flank of the eastern Piedmont and bound the eastern margin of the Durham sub-basin of the Deep River Triassic rift basin. Structures overprinting the western flank of the eastern Piedmont mark a late Paleozoic to Mesozoic ductile-to-brittle, strike-slip to dip-slip tectonic transition. This transition links structures and fabric elements thought to be widely separated in time and space into a progressive sequence reflecting transpressional hinterland buildup of a Pangean collisional orogenic zone and its extensional collapse during continental breakup.