Application of multi‐kinetic apatite fission track and (U‐Th)/He thermochronology to source rock thermal history: a case study from the Mackenzie Plain, NWT, Canada

Abstract

AbstractShale of the Upper Cretaceous Slater River Formation extends across the Mackenzie Plain of the Canadian Northwest Territories and has potential as a regional source rock because of the high organic content and presence of both oil‐ and gas‐prone kerogen. An understanding of the thermal history experienced by the shale is required to predict any potential petroleum systems. Our study integrates multi‐kinetic apatite fission track (AFT) and apatite (U‐Th)/He (AHe) thermochronometers from a basal bentonite unit to understand the timing and magnitude of Late Cretaceous burial experienced by the Slater River Formation along the Imperial River. We use LA‐ICP‐MS and EPMA methods to assess the chemistry of apatite, and use these values to derive the AFT kinetic parameter rmr0. Our AFT dates and track lengths, respectively, range from 201.5 ± 36.9 Ma to 47.1 ± 12.3 Ma, and 16.8 to 10.2 μm, and single crystal AHe dates are between 57.9 ± 3.5 and 42.0 ± 2.5 Ma with effective uranium concentrations from 17 ppm to 36 ppm. The fission track data show no relationship with the kinetic parameter Dpar and fail the χ2‐test indicating that the data do not comprise a single statistically significant population. However, when plotted against their rmr0 value, the data are separated into two statistically significant kinetic populations with distinct track length distributions. Inverse thermal history modelling of both the multi‐kinetic AFT and AHe datasets, reveal that the Slater River Formation reached maximum burial temperatures of ~65–90 °C between the Turonian and Paleocene, indicating that the source rock matured to the early stages of hydrocarbon generation, at best. Ultimately, our data highlight the importance of kinetic parameter choice for AFT and AHe thermochronology, as slight variations in apatite chemistry may have significant implications on fission track and radiation damage annealing in apatite with protracted thermal histories through the uppermost crust.