Kalin T. McDannell , Paul B. O'Sullivan, Kerry Gallagher, Scott Boroughs

Understanding the long-term erosion and burial history of cratons is challenging due to the incompleteness of the rock record. Low-temperature thermochronology is used to elucidate these surface histories by inverting thermochronological data for the time-temperature history and incorporating sparse constraints and other assumptions about the regional geologic evolution. However, imposing certain assumptions will influence the form of the inferred thermal histories, and in some cases this step may limit impartial assessment of the unknown history in terms of what features are required by the data and those that the data are consistent with (or at least do not contradict). Here we present a study involving laser ablation apatite fission-track data from three central Canadian Shield basement samples collected adjacent to the Hudson Platform Ordovician nonconformity in northern Manitoba and Ontario. Compared to a conventional fission-track analysis, our samples are characterized by up to ~3x the number of dated age grains and > 6–8x the number of track length measurements. The additional data improve inferences that are conditional on the data in Bayesian QTQt inversions, which in turn provide guidance on the potential conditions necessary for informing classical Frequentist inversions using the AFTINV software. Thermal history modeling is thus guided by a heuristic philosophy regarding the use of explicit constraints, which allows us to (i) examine the ability of the Bayesian model to independently infer geologically plausible time-temperature paths from the data (that is, assess sensitivity), (ii) compare the results with the known geology, and (iii) recursively parameterize models with respect to the previous results. QTQt models without time-temperature constraint boxes suggest two reheating events better explain the fission-track data (compared to a monotonic-cooling scenario) and indirectly imply periods at cooler, near-surface conditions in the latest Neoproterozoic to early Paleozoic, and in the Jurassic to early Cretaceous. The timing of such periods are consistent with major Hudson Platform unconformities. Collectively, best-fitting inverse thermal histories establish that the presently exposed basement near the Hudson Bay Basin experienced peak Paleozoic burial at ca. 317 ± 36 Ma (2σ). Burial could have occurred as early as Famennian or as late as Carnian time. A second burial event occurred in the latest Mesozoic to Tertiary at ca. 46 ± 30 Ma, but could have been as early as Aptian and as late as Chattian time. The sample furthest to the east nearer to the Moose River Basin may have experienced peak burial conditions earlier at 83 ± 14 Ma (within uncertainty of other models), synchronous with late Cretaceous sea-level rise. These estimates are in broad agreement with the preserved regional geology and previous thermochronology studies. However, our models support peak burial during Pennsylvanian and Eocene times, which could suggest a more extensive sedimentary cover than implied from preserved Hudson Bay Basin rocks (of well-known depositional age). Such histories are broadly consistent with Williston Basin and Slave craton burial history reconstructions to the west. Sedimentary rocks are estimated to have been ~1.4 ± 0.7 km (2σ) thick in the Paleozoic and ~1.5 ± 0.9 km thick in the latest Mesozoic to middle Cenozoic.