Analysis of joint set dispersion as an indicator of stress field variability in three structural provinces of the Ouachita orogenic belt, Oklahoma and Arkansas

Joint patterns in the central Ouachita Mountains indicate two temporally discrete stress phases. In the early phase, only exposed in lower Atokan and older rocks, the primary cross-fold joint strikes are NNE-SSW. The orientations of these joints were influenced by the development of local structures, especially the strike-slip transfer zones, in the central thrust belt and frontal imbricate zone. A two-stage deformation in this earlier phase is responsible for the structures in the frontal imbricate zone near Big Cedar, Oklahoma. The first stage, which reflects the northward regional transport direction in the Ouachita salient, results in east-west folds characteristic of the regional pattern in the central Ouachitas. In the second stage, a local recess forms near Big Cedar, OK where the Windingstair fault turns northwestward from its east-west strike as a consequence of differential displacement on the Windingstair fault and the Choctaw fault. As a result, the evolving recess causes the development of a pinch zone with a hinge at Big Cedar that induces east-west compression with a right-lateral slip component. The second phase of cross-fold jointing, seen throughout the central Ouachita mountains, indicates the NNW-SSE compression direction derived from the far field convergence of the Yucatan peninsula in the southeast.; Joint orientation in the Ouachita fold and thrust belt, while it can be predicted in a general regional sense, can not be predicted for nearby joints or outcrops with any certainty within the precision of the measurement on scales ranging from decimeter to kilometer. One or more joint sets of regional extent can be present among folded and faulted rocks. Among the small dip domains of the imbricated zone of the western Ouachita belt, between 25 and 50 randomly-selected outcrops are necessary in a 7.5&feet; quadrangle to sample the two regional joint sets. In the eastern imbricated zone of Arkansas, between 10 and 20 randomly-selected outcrops from a 7.5&feet; quadrangle detect the presence of one regional joint set. In the central thrust belt, between 5 and 10 randomly-selected outcrops over a 7.5&feet; quadrangle were sufficient to define two regional joint sets. In the Arkoma basin, between 5 and 10 randomly-selected outcrops permitted sampling of two joint sets, but this time over the larger area of a 30&feet; x 60&feet; quadrangle.; Joints are effective proxies for assessing the spatial parallelism and temporal constancy of stress orientations during joint growth. (Abstract shortened by UMI.)...