Timing, kinematics, and conditions of deformation of the Towaliga Fault Zone (Alabama)

Ben Clarke, Auburn University
Raphaël Gottardi, Auburn University
Mark Steltenpohl,
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Abstract

The Towaliga fault is a major structural feature of the southern Appalachian Piedmont developed during the Paleozoic Appalachian orogenesis, extending from eastern Alabama into central Georgia. Regionally, the Towaliga fault zone lies south of and subparallel to the Brevard fault zone, a major crustal-scale structure that records phases of prolonged ductile deformation followed by later brittle reactivation. The Towaliga fault zone is commonly interpreted as either a branch of this broader system or a kinematically related structure within the Inner Piedmont that accommodated similar deformation processes. The Towaliga fault zone is expressed as a wide and heterogeneous shear zone, locally reaching widths of up to ~6 km, characterized by mylonitic and ultramylonitic rocks along its core, surrounded by partially mylonitized schists, gneisses, and quartzites that define a broad damage zone. Structural observations indicate a northwest-dipping geometry and well-developed foliation, accompanied by abundant kinematic indicators generally consistent with dextral right-lateral shear, although variations in kinematics suggest a complex and evolving deformation history. Petrologic and microstructural analyses indicate that deformation along the Towaliga fault occurred under amphibolite- to greenschist-facies conditions and progressively transitioned to brittle–ductile and brittle regimes during exhumation. Timing of Towaliga fault zone deformation is poorly constrained. Sparse K-Ar cooling ages of ~300 Ma are interpreted to reflect the timing of late-stage movement or post-deformational cooling associated with the Alleghanian orogeny, but do not resolve the timing of earlier ductile shearing or subsequent reactivation. This study integrates field structural analysis, microstructural characterization, and thermochronologic data to better constrain the timing of deformation, quantify kinematic evolution, and refine the pressure–temperature conditions of fault zone activity. Our results provide new insight into the role of the Towaliga fault zone in strain partitioning and tectonic evolution of the southern Appalachian Piedmont.

Session

Deformation in the upper crust