Determining the structural development of basement-cored foreland arches is important to understanding the location, geometry, and fracturing of hydrocarbon reservoirs. The north-trending margin of the northeastern Front Range arch is oblique to the average northwest trend of Laramide folds. At the western margin of the Denver Basin, north-trending folds are oblique to northwest-trending folds within the Front Range arch. This bimodal distribution of fold orientations suggests either multistage deformation or a combination of regional and local effects.

Geometric analysis and paleostress inversion of data from minor faults indicate one horizontal compression event oblique to the arch margin which precludes multistage deformation. Changes in fold axis orientations and slip directions from west to east across the arch margin and preliminary 3D balancing support complex strain partitioning between north- and northwest-trending structures.

The northeastern margin of the Front Range arch developed due to backthrusting above a blind, northeast-directed basement thrust system. In the flank of the arch, oblique wedging of basement occurred as movement on the blind, ENE-directed Golden fault system was transferred to WSW-directed backthrusts and folds. Adjacent north-trending folds at the basin margin formed due to bending above the tip of the basement wedge. This variation in structural trends at the margin of the Denver Basin shows that deformation within basement-cored arches may not continue into adjacent basins.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah