REGIONAL ANALYSIS OF LARAMIDE DEFORMATION ACROSS THE COLORADO PLATEAU

Structural geology of the Colorado Plateau principally consists of thick-skinned Laramide deformation manifest as eight doubly plunging, asymmetric basement-cored uplifts with bounding fault-propagation monoclines that trend continuously for 100+ km. Located in the south-central part of the North American Cordillera, the Colorado Plateau province is a relatively undeformed region with vertical structural relief across uplifts ranging from ~1.5 to 2.5 km and regional horizontal shortening of <1%. These uplifts have been exhumed to shallow structural depths and generally root into blind basement shear zones. The blind nature of these structures limits hard constraints on characteristics of the controlling fault structure. To constrain blind fault geometries, we employed a novel technique based on linked kinematic and mechanical modeling. To constrain the geometry of the fault, we applied a trishear fault-propagation method along on serial cross sections to constrain the shallow 3D fault geometry and found the initial fault tip propagated from a depth near the basement-cover contact for most uplifts, which suggests a triggered reactivation along preexisting basement weaknesses. Trajectories of the faults at depth were further constrained through generalized area-depth relationships and are thus found to share a regionally-consistent average horizontal detachment depth of 27(±3) km. Local kinematic studies of these uplifts are complicated by variable paleostress indicators, indications of tectonic motion with significant obliquity, and structural asymmetry, raising questions about the regional stress environment that drove deformation. We evaluated regional tectonic driving stress across the Colorado Plateau by applying boundary-element dislocation modeling on a regional scale using 101 cross section interpretations to inform a 3D fault model. Elastic dislocation modeling yielded a best fit regional driving stress with far-field maximum compressive stress oriented ~060°, with 3D stress ratio of 0.25. By integrating these various structural approaches, we leveraged the limited available geologic data into a cohesive structural framework that is capable of testing previously unresolved questions around these iconic structures.