LITHOLOGIC, GEOMETRIC, AND KINEMATIC FRAMEWORK OF THE MACON FAULT ZONE AND RALEIGH TERRANE IN THE NORTH CAROLINA EASTERN PIEDMONT STATUS REPORT

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

For the past 7 years, the suprastructural, greenschist facies Spring Hope and infrastructural, amphibolite facies Raleigh terranes, as well as the Macon fault zone (MFZ), a major EPFS strand, have been the focus of NCGS mapping on the eastern limb of the Wake-Warren antiform. Previous mappers inferred 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 predicted that the MFZ evolved from east-directed thrust fault placing the Raleigh terrane over the Spring Hope terrane, to Alleghanian dextral subvertical shear zone.

New mapping in the Raleigh terrane supports the F₁-F₂-F₃ fold scenario, although the regional foliation is principally mylonitic or phyllonitic, and F₂ folds are tighter than described. F₃ folds produce shallow shear foliation dips and a wide fault zone exposure. A highly deformed mylonitic ridgeline that marks a major lithologic break between high-grade mafic-felsic gneiss and intermediate-grade white mica ± chlorite schist lies west of the currently mapped Raleigh-Spring Hope terrane boundary. The schist may be a lower amphibolite facies lithology within the Spring Hope terrane. Thus, the three fold generations present regional complications in lithologic map and fold interference patterns. It is crucial to work out the geometry of the deformed layers and kinematic elements in order to predict the location of the MFZ.