THREE-DIMENSIONAL DEFORMATION ANALYSIS OF QUARTZ ARENITES: IMPLICATIONS FOR OUACHITA MOUNTAINS TECTONIC DEVELOPMENT

The Ouachita Mountains are an exposed part of the Ouachita orogenic belt that extends from western Alabama through Mississippi, Arkansas, Oklahoma, and on to the Marathon region of southwestern Texas. The Ouachita system formed during the final assembly of Pangea in the Late Paleozoic. Consisting of clastic-dominated deposits from Cambrian to Early Atokan time, the Ouachita system represents a rather unique opportunity to study foreland structural processes in a clastic-dominated fold-thrust system. Although, the macroscale structure of the frontal zone has been well-studied, the complete kinematic history (i.e., micro- to macroscale) of this clastic-dominated fold-thrust system remains poorly documented. In this work, microstructural analyses are used to more fully constrain the kinematic development of a portion of the Frontal Zone and adjacent Arkoma Basin in the region around Hartshorne, Oklahoma. Our kinematic data set should yield information on variations in shortening direction and intensity along with data on the relative timing of thrust movements in the transition zone from the Frontal Ouachitas to the Arkoma Basin. The target units are the Pennsylvanian Spiro sandstone in the Frontal Zone and sandstones in the Pennsylvanian Krebs Group to the north in the Arkoma Basin. These quartz-rich sandstones provide appropriate markers for detailed microscale strain analysis. Oriented samples are analyzed with the aid of three mutually-perpendicular thin sections that are photographed under both transmitted light and cathodoluminescence. Finite strain magnitudes and orientations are being measured with the normalized Fry and Rf/f methods. These results can be combined to yield maps and cross-sectional profiles of depict variations in deformation intensity and direction. In addition to finite strain analysis, the abundance and relative timing of microscale deformation mechanisms will be determined via systematic point counting of microstructures. This work provides a starting point for a more complete kinematic analysis of the Ouachita Mountains tectonic system.