Rocky Mountain foreland uplifts; products of a rotating stress field or strain partitioning?

Stress-tensor analysis of minor faults near the structural range fronts of diversely oriented Laramide foreland uplifts in the central Rocky Mountains, Wyoming, indicates that paleo-sigma (sub 1) was horizontal and oriented nearly perpendicular to uplift trends. Trend directions for sigma (sub 1) vary from east-northeast in the north-trending Laramie Range, to northeast in the northwest-trending Bighorn Mountains, to north at east-trending Casper Mountain and in the east-trending central Owl Creek Mountains. Although these compression directions are compatible with models invoking temporally changing stress directions during the Laramide orogeny, the apparent similarity in timing of uplift in these ranges suggests that the computed stress tensors may not reflect regional stress conditions. Recent stress determinations in transpressional regimes suggest that strain partitioning may be an important factor in considering local stress patterns in the vicinity of mountain belt structures oblique to regional trends. In light of these studies, caution should be used in interpreting regional paleostress from structures measured close to the tectonic fronts of Laramide uplifts.