Three-dimensional finite-element modeling of a thin-skinned fold-thrust belt wedge: Provo salient, Sevier belt, Utah

Abstract

Three-dimensional finite-element (FE) analysis of a fold-thrust belt wedge model provides graphical and quantitative information for the strain geometry, kinematics, and mechanics of salient formation in three-dimensionalspace. A nonlinear, elastic-plastic FE model, using the initial basin configuration of the restored Provo salient, Utah, develops realistic deformation features (e.g., salient) in the deformed sedimentary prism. The three-dimensional fold-thrust belt wedge model shows different deformation characteristics (based on S 1 , γ m a x , and σ 1 orientations and material-displacement directions) in different parts of the salient, and its behavior is closely related to the preexisting template of the predeformational basin shape. The model results indicate plane-strain deformation with symmetric finite-strain geometry in the middle of the salient and nonplane-strain deformation with nonsymmetric finite-strain geometry at the lateral boundaries. Thus, conventional two-dimensional plane-strain assumptions in fold-thrust belt analysis (e.g., in balancing cross sections) are reasonable only in the middle of the salient; however, at the lateral boundaries, the results indicate fully three dimensional deformation and suggest that restorations need to be more carefully constrained in three dimensions on the basis of detailed geologic data.