EMPLACEMENT KINEMATICS OF THE EXOTIC PINE MOUNTAIN BLOCK, GEORGIA-ALABAMA: NO MISINTERPRETATION OF EXISTING DATA

The Pine Mountain window (PMW) in west-central GA and east-central AL is framed by the Tugaloo terrane (Inner Piedmont) in most of GA. The cover sequence in PMW contains 1.1 and 2.0-2.4 Ga detrital zircons, indicating an Amazonian source and PM block is exotic (Steltenpohl et al.). Alleghanian faults exhibiting different rheologies flank the PMW indicating the faults are not coeval. NW-directed thrusts at peak sillimanite I conditions (E flank; Box Ankle fault, BAF, Rumble shear zone, RSZ), later dextral strike slip at garnet grade (N & E flanks, & internal; Towaliga, TF, Ocmulgee-Central Piedmont suture, OFCPS, Bartletts Ferry?, BFF, Goat Rock?, GRF, faults), and even later chlorite grade dextral strike slip (S flank; Dean Creek-Modoc fault, DCMF) faults occur here, and formed incrementally as the orogen unroofed. Interconnected Jurassic sinistral plastic to semibrittle faults and right stepovers obliquely (<20°) cross the N flank of the window (TF). Proposed kinematic sequence for PMW elements: (1) Early Paleozoic(?) deposition near Gondwana of PMW cover sequence on 1.1 Ga crust; (2) Middle Paleozoic (MPZ; Devonian?) accretion of PM terrane to Laurentia; (3) MPZ (Devono-Mississippian) accretion of Carolina terrane, partial subduction beneath Carolina of Tugaloo and Cat Square terranes (central Piedmont suture/330 Ma OFCPS), and 305 Ma BAF thrusting and RSZ; (4) Upper mid-crustal dextral strike-slip escape and imbrication of the PM block along the TF, BFF, and GRF (~300 Ma) with localized apparent normal slip along TF related to upward escape of the PM block (numerical forward modeling indicate TF and adjacent IP and PMW geometries are incompatible with TF normal displacement); dextral SW propagation of the eastern Piedmont fault system and the DCMF (~280 Ma?); and (5) Permian head-on collision of Gondwana with Laurentia producing the Blue Ridge-Piedmont megathrust sheet propagating along the ductile-brittle transition beheading all earlier terranes, including the PM block (subhorizontal reflections 11-12 km deep in reprocessed COCORP data), transporting them onto the Laurentian platform.