Effect of predeformational basin geometry in the kinematic evolution of a thin-skinned orogenic wedge: Insights from three-dimensional finite element modeling of the Provo salient, Sevier fold-thrust belt, Utah

摘要

In fold-thrust belts, sedimentary cover rocks are detached from undeformed basement and undergo crustal-scale shortening and internal deformation. We have investigated a three-dimensional (3-D), nonlinear, elastic-plastic finite element model using the restored Provo salient of the Sevier belt as our initial configuration. In the model the deformed sedimentary prism displays large-scale geometries that are seen in many natural fold-thrust belts (e.g., arcuate salient, wedge-shaped cross section) and kinematics that are compatible with observations in the internal and external portions of the Provo salient; these suggest that the model can be used to predict geologic information that is generally not available from detailed observational studies in natural fold-thrust belts (e.g., strain history, material displacements, stress conditions). The model results indicate symmetric, noncoaxial, plane strain paths with consistent stress and strain orientations and material displacement directions in the middle of the 3-D wedge, and fully 3-D, nonsymmetric, noncoaxial, nonplane strain paths with out-of-transport material displacements over the lateral boundaries. The results from test runs further suggest that oblique ramps with strike direction less than 20° from the regional transport direction behave like lateral ramps, and those with strike direction greater than 80° from the regional transport direction behave similar to frontal ramps. Oblique ramps with dips greater than 60° behave like tear faults. These variations in different parts of the wedge are caused mainly by interaction between the transport parallel motion of the moving wedge and the preexisting footwall template of ramps and flats that the wedge has to ride over during its evolution.