Abstract

Measurement and statistical analysis of tectonic stylolite teeth trends in the Big Bend region signify that a compressive event of constant mean trend (N58°E) was responsible for deforming the entire region during Laramide orogeny. However, developing structures locally altered this stress field trajectory in a feedback mechanism at two tectonic scales. The first, represented by changes in the “regional” stress field trajectory from west to east across the Big Bend region, resulted in an average 5° clockwise curvature in stress trajectory. Additional Laramide σ₁ stress field variations, displayed in stress field trajectory maps, were encountered at more local levels across the Terlingua uplift and Boquillas Canyon areas. The stress field curves about 31° counterclockwise as the Terlingua monocline is approached from the north. Likewise, a 15° counterclockwise stress field curvature exists from west to east in the Boquillas Canyon area. These stress field curvatures result from contemporaneously developed structures which locally altered the shape of the field. Knowledge of stress trajectories may be important for identifying fracture trend variations near faults in producing oil and gas fields, and in analyzing faults in earthquake studies.