A QUANTITATIVE APPROACH TO UNDERSTANDING REGIONAL STATES OF PALEOSTRESS, APPLIED TO LARAMIDE TECTONICS ON THE COLORARDO PLATEAU

Engaging a variety of structural modeling approaches can help increase confidence in interpreting regional tectonic paleostress conditions, which can provide significant insight into tectonic drivers and structural development. Wide ranging far-field stress conditions can be evaluated by applying boundary-element dislocation modeling to constrained structural geometries and comparing the modeled to observed structural relief patterns on a regional scale. This methodology is applied to Laramide deformation patterns on the Colorado Plateau. On the plateau, Laramide-style deformation is evidenced by ten doubly plunging uplifts and their associated monoclines which individually span hundreds of kilometers in length with up to two kilometers of structural relief. Detailed structural studies of these uplifts are often complicated by variable local paleostress indicators, tectonic motion with significant obliquity, and structural asymmetry. Interpretation of these variably-oriented uplifts is further complicated by the fact that they generally root into a blind basement shear zone resulting in limited exposures to provide hard constraints on the location and orientation of controlling fault structure. Because of this, previous studies have not converged on a consistent interpretation of Laramide regional 3D paleostress state, associated tectonic drivers, or principle controls on uplift formation. Applying various structural modeling techniques has aided our understanding of regional paleostress state from initially enigmatic field observations. In order to constrain blind 3D fault geometries, we have applied trishear fault propagation fold modeling to serial transects across each of the structures, with trajectories at depth constrained through generalized area-depth relationships. We then applied boundary-element dislocation modeling to interpreted 3D fault geometries testing various orientations and relative principal stress magnitudes to constrain the best-fitting Laramide state of stress to match the observed structural patterns on the Colorado Plateau. By integrating these various modeling approaches, we leverage the limited available data into a cohesive structural framework that is capable of testing previously unresolved questions around these iconic structures.