NEW PERSPECTIVE ON LATE PALEOZOIC SLIP HISTORIES ALONG THE MACON FAULT ZONE, EASTERN NORTH CAROLINA PIEDMONT

In the eastern North Carolina Piedmont, the eastern Piedmont fault system, composed of 8 plastic-brittle fault strands, cuts Neoproterozoic-Cambrian island-arc rocks into 9 terranes during Alleghanian orogenesis. It also affects Pennsylvanian granites related to the Rolesville batholith. The Macon fault zone (MFZ) is a member of this system. It is a 4-6-km wide, NE-striking, NW-dipping mylonite zone juxtaposing the western, amphibolite Warren terrane against the eastern, greenschist Spring Hope terrane. Prior mapping indicates it has both dextral and thrust components. EDMAP mapping in the southwestern Inez 1:24K Quadrangle suggests that the MFZ also experienced tops-down-NW, plastic-brittle extension.

From west to east across the Inez area, the intensity of deformation and metamorphism decreases. In the MFZ, the Warren and Spring Hope terrane record these fabric elements: (1) transposed compositional layering, S₀; (2) penetrative schistosity, S_1S; (3) crosscutting mylonitic foliation, S_1C; (4) extensional shear bands, S_1C’; (5) obliquely NW-plunging aggregate and rod lineation, L₁; (6) steeply NW-plunging, NE-verging, upright/steeply inclined folds, F₁ of S_1S-S_1C; (7) crenulation cleavage, S₂ to gently plunging, upright folds, F₂ that refold F₁; (8) mica “fish” and tailed porphyroclasts; (9) kink bands, S₃, and (10) domains of vein fiber lineation, L₂, and brittle faults, microfaults and fractures, S_f. Terrane-stitching granites also contain mylonite shear zones. East of the MFZ, the Spring Hope terrane has a regional schistosity, S_rs, in less strained and lower grade rocks. There, upright, gently NW-plunging folds overprint S_rs and may be related to F₂ within the fault zone. There is no clear evidence that these rocks experienced the same mylonitization as rocks in the MFZ.

Kinematic indicators normal to S_1S-C consistently show dextral slip in the MFZ. Tops-down-NW asymmetry occurs parallel to plastic L₁ and brittle L₂. Fabric geometry is compatible with tops-down-NW extension. Across the Inez area, S_1S-C and fault traces step east from NE to E-W to NE strikes across a small separation. A right stepover, combined with fabric geometries and kinematics, may reflect the evolution of a strike-slip releasing bend along this section of the MFZ, similar to other regional dextral fault strands.