A 3-DIMENSIONAL GEOMECHANICAL FINITE ELEMENT METHOD COMPARISON BETWEEN MODELS OF CONTINENTAL BOUNDARY TECTONISM EXPLAINING THE ANCESTRAL ROCKY MOUNTAIN OROGENY

Late Paleozoic amalgamation of Pangaea was marked in southern Laurentia by east-to-west sequential suturing of the Ouachita-Marathon orogenic belt, and intracontinental uplifts of the Ancestral Rocky Mountains. Recent studies propose two classes of models (2- and 3-sided) to explain the presence, orientation, and intensity of Ancestral Rocky Mountains deformation. In a two-sided model, transpression or oblique collision on the western margin and minimally compressive transform tectonism on the southwestern (Sonoran) margin are combined with Ouachita-Marathon fold belt closure. In a three-sided compression model, the forces from the sequential closure of the Ouachita-Marathon fold belt are combined with the direct compression on the western boundary and long-lived transpressional force on the Sonoran boundary to explain uplifts and basins.

This study compares the evolution of stress and strain between 3D geomechanical finite element domains representing Laurentia for the sequential closure, two-sided, and three-sided compression models of the Ancestral Rocky Mountain Orogeny. The evolution of stress and strain is calculated over sixteen million simulation years with velocity boundary conditions approximating each tectonic hypothesis. Boundaries of Laurentia are restored to their pre-Ancestral Rocky Mountain Orogeny configuration utilizing estimates from published palanspastic restorations and geochemical trends.

The results of this work will be presented in terms of strain and differential stress buildup in the continental domain caused by each tectonic boundary condition. The degree to which strain and differential stress trends align with established trends of major and minor uplifts and the timing of their formation will be highlighted. Preliminary results indicate that it is not necessary to invoke northeast directed compression on the Sonoran boundary nor active compression or transpression on the western margin to generate east-west and north-south differential stress in trends coincident with known uplifts. However, compression or transpression on the western margin enhances the development of stress and strain in these regions.