GEOMETRY OF THRUST TRAJECTORIES IN THE SOUTHERN APPALACHIAN HINTERLAND OF GEORGIA AND ALABAMA

In the Appalachian Blue Ridge and Inner Piedmont of Georgia and Alabama, breached regional folds trending oblique to regional strike produce 1/2-windows allowing for a 3-D view of the hanging and footwall geometries, and analysis of regional kinematic relationships of the crystalline thrust sheets exposed within these structures. The bounding faults are all low-angle Alleghanian thrusts that telescoped the previously deformed and metamorphosed Laurentian outer margin stratigraphy, significantly shortening that margin (>150%), generally placing higher grade rocks on lower grade rocks, and cutting obliquely through lithostratigraphy, peak metamorphic fabrics (early Carboniferous), and previously emplaced thrust sheets. With respect to much of the deformation in the SE parts of the foreland thrust wedge, most of the frontal hinterland thrusts are “out-of-sequence.” These faults include: A) The Talladega-Cartersville fault (minimum horizontal component of net slip (MHCNS) of 23 km), is oblique to cleavage, and stratigraphy in both hanging and footwalls, cuts progressively structurally downward through several major foreland thrust sheets toward the SW, and decapitates map-scale folds in both hanging and footwalls. B) The Hollins Line/Burnt Hickory Ridge faults (MHCNS of 19 km), a footwall transpressional duplex that imbricates but is semi-concordant to footwall lithostratigraphy, cuts down section to the NW in the hanging wall obliquely through the metamorphic fabrics and >12 km of lithostratigraphy. C) The Allatoona fault (MHCNS of 14 km), decapitates map-scale folds and cuts down section to the NW in its footwall obliquely through the metamorphic fabrics and >11 km of lithostratigraphy. D) The Katy Creek/Stonewall Line fault (MHCNS of 50 km) exhibits a ramp-on-flat geometry with the thrust sub-parallel to its footwall, but cuts up section to the NW through ~14 km of hanging wall ramp stratigraphy. The Hillabee thrust (MHCNS of 18 km) is an exception to those above, being a cryptic pre-metamorphic fault that is concordant to both hanging and footwall sequences (flat-on-flat geometry) across its entire extent (mapped palinspastically >4,600 km²). With the exception of the Hillabee thrust sheet, the other thrust sheets were metamorphosed and polydeformed >40 m.y. before final emplacement (Permian?).