THE MACON FAULT ZONE: LITHOLOGIC, GEOMETRIC, AND KINEMATIC FRAMEWORK OF A FOLDED ALLEGHANIAN SHEAR ZONE, EASTERN PORTION OF THE AFTON QUADRANGLE, WARREN COUNTY, NORTH CAROLINA

The North Carolina eastern Piedmont exposes an array of metamorphic, plutonic, and sedimentary rocks spanning from the Neoproterozoic to the Cenozoic. The metamorphic rocks are part of the 633-528 Ma Carolinia superterrane, a(n exotic) peri-Gondwanan island-arc system that was amalgamated to the eastern Laurentian margin in the mid-Paleozoic. The Eastern Piedmont fault system (EPFS), a late Paleozoic-Mesozoic ductile-brittle fault network, dissected the eastern portion of Carolinia into smaller regional terranes during Alleghanian orogenesis. These terranes differ in proportions of magmatic and volcanogenic sedimentary rock types, environments of formation, and crustal levels of tectonothermal overprint.

For the past 8 years, the NC Geological Survey has focused its mapping on the eastern limb of the Wake-Warren antiform where the infrastructural, amphibolite facies Raleigh and suprastructural, greenschist facies Spring Hope terranes are in contact along the Macon fault zone (MFZ), a major EPFS strand. Prior mapping determined a regional scenario involving three folding events. Northwest- or southeast-plunging isoclinal F₁ folds overprint compositional layers. North to northwest-plunging open F₂ folds and northeast-southwest-plunging F₃ folds overprint regional foliation. Strain is inferred to increase in the eastern Raleigh terrane along the MFZ. It is suggested that the MFZ evolved from an east-directed thrust fault placing the Raleigh terrane over the Spring Hope terrane, to a subvertical Alleghanian dextral shear zone. While segments of the MFZ have been studied regionally, there are still portions that lack detailed mapping.

New mapping in the Raleigh terrane supports the polyphase fold history, although the first generation is rarely observed due to the strong overprinting of later fold generations. Also, a high-strain gradient may mark a lithologic break between Spring Hope terrane schist and Raleigh terrane gneiss and is further west than previously mapped. The MFZ appears to be a folded, shallowly dipping, high-strain shear zone that places amphibolite facies Raleigh terrane over greenschist facies Spring Hope terrane. Deformed Pennsylvanian-Permian plutons constrain the MFZ to the Late Paleozoic Alleghanian orogeny.