Cretaceous to Miocene exhumation of the Purcell Mountains, southeastern British Columbia

The southeastern Canadian Cordillera records post-orogenic extension and core complex formation west of the Rocky Mountains. Geochronology and emplacement depth estimates of intrusions revealed that the Purcell Mountains, located on the interface between the Rocky Mountains and core complexes in the in the Selkirk and Monashee Mountains, underwent >10 km of exhumation since the latest Cretaceous. We investigate the Cenozoic exhumation history of the Purcell Mountains by combining metamorphic petrology and low-temperature thermochronology. We first determine the emplacement depths of two intrusions that span most of the width of the Purcell Mountains. Observed mineral assemblages along six transects through the contact aureoles range from cordierite + andalusite-bearing assemblages in the eastern White Creek aureole to staurolite + andalusite-bearing assemblages in the western Fry Creek aureole, suggesting emplacement depths that range from 8.3–13.6 km to 10.5–14.7 km, respectively. The post-emplacement cooling history is assessed using zircon and apatite (U-Th)/He and apatite fission track thermochronology. These data indicate that 6–8 km of exhumation occurred in the Purcell Mountains between 66 and 30 Ma with accelerated rates between 40 and 30 Ma. An additional 3–6 km of exhumation is recorded between 30 and 0 Ma on the western flank of the Purcell Mountains suggesting reactivation along the Gallagher fault zone. In contrast, an intrusion in the western Rocky Mountains records 2–4 km of exhumation in the Late Cretaceous (108–66 Ma), <2km between 66 and 40 Ma, and 2–3 km during the 40–30 Ma accelerated phase.