TECTONIC EVOLUTION OF THE OUACHITA MOUNTAINS FRONTAL ZONE AND ARKOMA BASIN: INSIGHTS FROM MICROSTRUCTURAL ANALYSES

The Ouachita Mountains in southeastern Oklahoma and western Arkansas represent the exposed part of the larger Ouachita Orogenic System that extends from western Alabama to southwestern Texas. The system was dominated by Paleozoic shallow to deep-water deposition on the rifted, southern margin of Laurentia after the break-up of Rodinia. Convergent processes replaced tectonic quiescence in the late Paleozoic as subduction developed during the final assembly of Pangea. As a result, imbricated Pennsylvanian rocks in the Ouachita frontal zone are separated from the mildly-deformed, Pennsylvanian (and younger) Arkoma Basin by the Choctaw fault. While frontal zone macrostructures are well-studied, the kinematics remain incomplete since the role of smaller-scale processes is poorly understood. Here, we present microstructural analyses that a focus on more fully constraining the kinematics in the frontal zone and Arkoma Basin. The data includes spatial variations in shortening direction and intensity along with changes in deformation conditions as reflected by deformation mechanisms.

The target units are the Pennsylvanian sandstones that are well-exposed and provide appropriate markers for detailed microscale strain analysis. Oriented samples were photographed and analyzed with transmitted light and cathodoluminescence. Normalized Fry and Rf/f methods yield finite strains that are used to assess variations in magnitude and orientation both across and along strike. Microscale shortening computed across the frontal zone and Arkoma Basin can be added to established macroscale estimates to provide a more complete kinematic analysis. Deformation mechanism timing and abundance determined via microstructural point counts provide indications of spatial and temporal changes in deformation conditions.