Geologic investigations in the central Georgia Inner Piedmont and the western flank of the Carolina superterrane: Implications regarding Acadian and Alleghanian collisional orogenesis, fault reactivation, and the Mesozoic breakup of Pangea

Detailed geologic mapping, U-Pb geochronology, igneous petrology and whole-rock geochemical analysis, and structural analysis of the Inner Piedmont and Carolina superterrane were conducted to better define the tectonic history of the southern Appalachian orogen; results yield implications for Acadian/Neoacadian and Alleghanian collisional events and Mesozoic breakup of Pangea. Detailed geologic mapping was focused in the Inner Piedmont at the northeastern end of the Pine Mountain window to investigate an aeromagnetic anomaly that was hypothesized to represent the southwestern continuation of the Brindle Creek fault, which separates the Inner Piedmont terranes (Tugaloo and Cat Square). Evidence supports this hypothesis, while contrasting detrital zircon and metamorphic ages provide insight regarding the paleogeographic position of the Cat Square terrane during deposition, and to processes related to mid-crustal flow in orogenic systems.

Two tectonic models that differ in timing, kinematics, and subduction polarity have been proposed to describe accretion of the Carolina superterrane. Geochronologic and geochemical analysis of mafic plutons better define their timing and petrogenetic origin; data are consistent with derivation in a subduction-zone setting. Emplacement predates main-phase Cat Square terrane plutonism, which is a product of east-dipping B-subduction beneath the Carolina superterrane followed by shutoff of arc-magmatism during A-subduction of the eastern Laurentian margin that resulted in metamorphism and anatectic plutonism in the eastern Inner Piedmont. A hybrid tectonic model synthesizes numerous data from the orogen.

The Towaliga fault contains tectonites that formed under various P-T conditions, revealing a complex reactivation history. Towaliga fault garnet-grade mylonite formed during large-displacement Alleghanian dextral strike-slip, while isolated, km-scale rhomboidal silicified cataclasite pods likely represent ancient dilational step-overs that formed in a small-displacement sinistral strike-slip system during the Mesozoic breakup of Pangea.

The Pine Mountain terrane has a polyphase allochthonous emplacement history that can be delimited by its bounding faults, regional fabric and crosscutting relationships. Palinspastic restoration indicates the Pine Mountain terrane may have originated near the Virginia promontory. The current configuration of the Pine Mountain terrane far outboard in the orogen, combined with its near-shore Neoproterozoic-Cambrian cover strata, suggest it may represent a peri-Laurentian microcontinent that rifted from the margin sometime in the Cambrian.