The impact of continental shape in 3D geomechanical models of ancient orogenic belts: An example from the Ancestral Rocky Mountain orogeny

The orientations of ancient intra-cratonic uplifts are commonly used to interpret the boundary tectonism style along concealed, modified, or destroyed continental margins. An implicit assumption is that the tectonism-linked stress field strongly correlated with uplift orientations. However, among other uncertainties, the shape of a stressed domain likely has an influence upon the interior stress field. In many cases of pre-Cenozoic orogenesis, multiple feasible restorations of a continent margin exist. To explore the influence of continent margin position and shape on a hypothetical ancient continental stress field we developed a new 3D geomechanical finite element method (FEM) to evaluate scenarios for the late Paleozoic Ancestral Rocky Mountain orogen (ARMO). Tectonic scenarios were calculated across a range of domains constrained by geologic uncertainty in the pre-ARMO geometry of the continent. Uncertainty for continent geometry prior to the ARMO is estimated from several published palinspastic restorations. The results demonstrate that 10s–100s of km of uncertainty in margin position, as is the case of the ARMO, should not prevent the linkage of stress patterns to styles of boundary tectonism. This work shows it is plausible to simplify the analysis of the ARMO stress/strain field utilizing one continental geometry.