ABANDON THE LARAMIDE: THE SOUTHWEST U.S. IS PART OF THE MEXICAN CORDILLERAN OROGENIC WEDGE

Late Cretaceous to Eocene deformation, magmatism, mineralization, and sedimentation in the southern U.S. and northern Mexican Cordillera, the Borderland, is commonly attributed to the Laramide Orogeny. However, apart from timing, this region shares very few similarities with the archetypal Laramide Orogeny in the central to northern U.S. Rocky Mountain region and is difficult to reconcile with many tectonic and geodynamic models. The most diagnostic characteristics of the Laramide Orogeny, including large basement-involved uplifts, broad peripheral basins in a broken foreland, and the cessation of magmatism, are not observed in the southwest U.S. and northwest Mexico. On a regional scale, this part of the Cordillera exhibits features consistent with a classic orogenic wedge including deeper structural levels exposed in the hinterland and deformation progressively moving up structural-stratigraphic section toward the foreland. The age of deformation, regional orientation of structures, spatiotemporal patterns of magmatism, and commonality of hinterland features suggest that the Borderland is part of the Mexican orogenic wedge, the southernmost segment of the North American Cordillera.