TECTONIC EVOLUTION OF THE PALEOZOIC SE LAURENTIAN MARGIN: GEOLOGIC CONSTRAINTS FROM THE SOUTHERN OKLAHOMA AULACOGEN

Interplay between marginal and intraplate late Paleozoic tectonics in southeastern Laurentia is a subject of debate. In southern Laurentia, intraplate deformation has been attributed to combinations of compressive forces from orogenic belts in the west, southwest, and southeast. Combinations of compression and left-lateral strike-slip are generally accepted mechanisms for formation of uplifts in the Southern Oklahoma Aulacogen (SOA). We have analyzed the Southern Oklahoma Transpressional System (SOTS), a ~500 km long ~50 km wide fault zone that extends from the southeastern Laurentian margin into the plate interior along Cambrian lithospheric weaknesses inherited from the SOA. We construct detailed, time-integrated sedimentary thickness maps of SOTS-related basins and fault zones from literature and from a new interpretation of three 2D seismic reflection lines. We conclude that diachronous closure of the Rheic ocean basin between Laurentia and Gondwana was driven by slab-pull forces on the sinking oceanic plate, which began to detach and/or tear as collision progressed. We propose a conceptual model where diachroneity of oceanic basin closure, and irregular SE Laurentian margin morphology caused variations in distribution of slab-pull forces along the southern Appalachian and Ouachita-Marathon fronts. The resulting irregular force distribution caused clockwise rotation of the local SOTS stress field, changing SOTS kinematics during late Paleozoic time. We infer that these driving mechanics caused most major SOTS fault zones to evolve from ~orthogonal contraction to left-lateral strike-slip during Mississippian-Pennsylvanian time, which can be explained by rotation of the stress regime. We propose that Mississippian faulting was driven by a NE-striking σ1, and that subsequent clockwise rotation of σ1 to more E-striking fits well with late Pennsylvanian fault kinematics.