Metamorphic core complexes (MCCs) are domal geological structures that result from the exhumation of the mid-to-lower crust (e.g., Crittenden et al., 1980). These structures are significant because they represent locations of extreme crustal extension and provide illuminating windows into the thermomechanical properties of Earth's lithosphere (e.g., Platt et al., 2015;Whitney et al., 2013). First described in the western United States, MCCs consist of a ductilely deformed metamorphic-plutonic footwall separated from a brittlely deformed hanging wall by a low-angle normal fault (detachment fault) (Armstrong, 1982;Coney, 1980;Wernicke, 1981). Despite their widespread occurrence and tectonic significance, the origin of core complexes-specifically the regional tectonic processes that facilitate footwall exhumation from mid-crustal depths-remains controversial (e.g., Konstantinou et al., 2013). Several orogen-scale dynamic models have been proposed for MCC formation in the North American Cordillera, including: (a) a change in plate motions, (b) dynamic processes of the downgoing slab (e.g., slab rollback), and (c) late or post-orogenic collapse due to overthickened continental crust (e.g., Whitney et al., 2013). In the North American Cordillera, MCCs form an N-S trending belt that traces a pre-extensional lithospheric welt, where crustal thicknesses and