Three-dimensional evolution of a fold-thrust belt salient: Insights from a study of the geometry, kinematics and mechanics of the Provo salient, Sevier Belt, Utah, and from three-dimensional finite element modeling

Most fold-thrust belts (FTBs) have prominent arcuate map patterns with thrust traces convex toward the foreland giving rise to a pattern of salients; the along-strike variations in adjoining salients are typically decoupled from one another along transverse zones that form recesses in the FTB. This pattern of salients and recesses reflects the 3-D nature of deformation within FTBs. The Provo salient of the Sevier FTB in Utah, and its bounding oblique transverse zone (viz. Leamington zone), preserve evidence for elucidating the 3-D evolution of the FTB.; The Leamington zone (LZ) consists of the first-order Leamington Canyon thrust (LCT), associated second-order asymmetric folds and a first-order out-of-syncline reverse fault.{09}A detailed study of the structural geometry of the LZ suggests that it serves as an accommodation zone between structures (e.g. Canyon Range thrust and Tintic Valley thrust) at the boundary between two prominent salients (viz. Provo salient and Central Utah segment) of the Sevier FTB in west-central Utah.; A detailed kinematic study along the LZ reveals three different stages of superimposed deformation that has ramifications for the Provo salient evolution. These progressive deformation patterns that are preserved along the LZ reflect temporal changes in tectonic transport over the oblique ramp as the overall easterly displaced 3-D FTB wedge has interacted with the pre-existing oblique ramp structure. There are also small amounts of superimposed local vertical-axis rotations during later folding and fold-tightening of the folded LCT.; Detailed kinematic history study of mesoscopic and microscopic structures from the Provo salient are used to distinguish between five end-member models of salient formation. Our analysis shows that individual thrust sheets within the Provo salient evolve in different ways at different times. The results further indicate that a salient can have a long and complex deformation history during its evolution.; A geologic-scale 3-D wedge finite element model, using the initial basin configuration of the restored Provo salient, reproduces a number of first-order characteristics seen in the natural FTB. The model FTB wedge experiences different finite strain shapes, strain geometry, kinematics and mechanics of deformation in different portions such as in the middle versus oblique and/or lateral ramps. The numerical modeling is useful for predicting history of strain geometry, material displacement and mechanical conditions related to the evolution of the Provo salient that are not available from detailed structural studies.