Thermal history of the Peel Plateau, northern Canadian Cordillera, resolved through multikinetic apatite fission-track dating

Abstract

The Peel Plateau of the northern Canadian Cordillera has undergone multiple burial and unroofing events throughout the Phanerozoic, including subsidence and uplift associated with emergence of the Mackenzie Mountains. Episodic unroofing events are evinced by unconformities that represent a period where an unknown amount of material was deposited and eroded. Thermochronological studies have been conducted in neighboring physiographic regions, however no work has been conducted in the Peel Plateau and there is interest to determine whether it shares a similar thermal evolution as the surrounding regions. Apatite fission-track thermochronology (AFT) is a useful method for reconstructing basinal thermal histories as the system is sensitive to upper crustal temperatures, although the kinetics of the thermochronometer are complicated by numerous elemental substitutions within apatite that are known to control the specific temperature window within which fission-tracks anneal. This study uses three strategically positioned AFT samples from Phanerozoic sedimentary rocks to investigate the thermal history of the region from the Devonian to the present. Pooled AFT ages from all samples fail the χ2 test, implying there is a high level of intra-sample age dispersion and potentially indicating the samples contain multiple age populations. To assess whether the data are consistent with multiple kinetic AFT populations, we use grain-specific apatite compositions to derive rmro, a kinetic parameter that accounts for elemental substitutions known to control annealing kinetics of fission-tracks. By plotting AFT ages and track lengths against rmro we identify more-retentive and less-retentive apatite populations within each sample, which serve as independent thermochronometers when incorporated into inverse thermal history modelling. Results from a thermal history model of the Upper Devonian Imperial Formation indicate that the uppermost Paleozoic strata in the Peel Plateau reached maximum burial temperatures (∼165°C–185 °C) in the Triassic and were reheated to lower temperatures (∼90°C–100 °C) under a Cretaceous-Paleocene foreland basin. The temperature regime of the latter burial event is supported by thermal history models of two Cretaceous samples that record peak burial temperatures (∼80°C–90 °C) in the Paleocene to Eocene. This study highlights the capabilities of thermal history modelling from multikinetic AFT data and serves as a reminder that addressing variable annealing kinetics of apatite grains can improve the resolution of thermal models and the associated geologic interpretations.