Zircon (U‐Th)/He thermochronology of Neoproterozoic strata from the Mackenzie Mountains, Canada: Implications for the Phanerozoic exhumation and deformation history of the northern Canadian Cordillera

Abstract

Sedimentary strata of the Neoproterozoic Mackenzie Mountains Supergroup (MMSG) and Windermere Supergroup (WSG) occupy the cores of anticlines in the Mackenzie Mountains of the Canadian Cordilleran Foreland Belt. Stratigraphic and structural evidence suggest that these rocks have undergone several episodes of burial and unroofing relatively intact. We report single‐grain detrital muscovite 40Ar/39Ar and zircon (U‐Th)/He (ZHe) data from a suite of samples across the fold‐thrust belt and the Neoproterozoic stratigraphic record. The strata have not reached high enough temperatures to reset the muscovite 40Ar/39Ar system, and instead our detrital muscovite data refine Tonian‐Cryogenian depositional ages. Single‐crystal ZHe dates range from 432 ± 35 to 46 ± 4 Ma, indicating that MMSG and WSG strata have not been heated sufficiently to fully reset the ZHe system. These factors make the Neoproterozoic strata an attractive natural laboratory to test the utility of the zircon radiation damage and annealing model on the quantification of thermal histories from detrital zircon populations that have accumulated radiation damage over long geologic timescales. Thermal modeling reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo‐Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75–67 Ma in the southwest and 60–55 Ma at the deformation front. Ultimately, relationships between radiation damage and helium diffusion kinetics in zircon explain substantial ZHe date dispersion and elucidate the temperature‐time history of the northern Canadian Cordillera.

Fault Slip and Exhumation History of the Willard Thrust Sheet, Sevier Fold‐Thrust Belt, Utah: Relations to Wedge Propagation, Hinterland Uplift, and Foreland Basin Sedimentation

“…Understanding sources of intrasample dispersion in grain cooling ages is important for evaluating uncertainties in thermochronometric interpretations and optimizing sampling design. Most samples in this study displayed greater dispersion in ZHe grain ages (typical 1σ ~10% of mean age) than expected for analytical uncertainty (~4% of grain age), similar to results of other studies (e.g., Wolfe & Stockli, ; Guenthner et al, ; Powell et al, ; Ault et al, ), partly related to varying radiation damage that affects He diffusion (Guenthner et al, ). Grains were selected for ZHe analysis based on similar eU contents (mostly 30 to 300 ppm) and U‐Pb ages (mostly 2.0–1.0 Ga), and thus similar values of maximum accumulated radiation damage.…”

Thermochronological Evidence of Early Orogenesis, Eastern Pyrenees, France

“…Nonetheless, the two scenarios are so similar that the current calibration of the Guenthner et al () model does not allow us to differentiate between them. It is important to stress that here we have reached the model's limitations emanating from its parameterization requirements, as already detected by previous authors (Powell et al, ; Vacherat et al, ). We note that this model cannot simulate the older ages of our data set for any thermal history with maximum temperatures during rifting (120–95 Ma in simulations) higher than 190 °C (e.g., scenarios 4, 5, 9, 10, 14, and 15).…”

“…This result also clearly illustrates the difficulty in identifying a single t ‐ T history using ZHe ages plotted against eU. As recently noted by some authors in other geologic settings (Anderson et al, ; Johnson et al, ; Powell et al, ; Vacherat et al, ), forward modeling suggests that the damage‐dependent model of diffusion is able to reproduce only qualitatively, not quantitatively, the range of single‐grain ZHe ages and both positive and negative age‐eU correlations. This probably also explains the failure of the HeFTy software to produce plausible thermal histories when performing inverse modeling with too many input data.…”

“…The most recent, rapid cooling history of a sample or a group of samples is dated at opposite ends of the eU concentration spectrum, irrespective of any earlier history. Any earlier thermal histories shape age‐eU correlations for maximum predicted ages and constrain any positive and/or negative correlation trends for these older ages (referred to as the ZHe inheritance curve; Guenthner et al, ; Powell et al, ). This point is illustrated with some sensitivity tests in Figures S5 and S6 and will be discussed below.…”

Deciphering a 2 Gyr‐Long Thermal History From a Multichronometer (U‐Th)/He Study of the Phalaborwa Carbonatite, Kaapvaal Craton, South Africa

“…Advances in (U‐Th)/He thermochronology provide new potential to address this problem. The strong influence of radiation damage on the He retentivity of apatite, zircon, and titanite means that (U‐Th)/He data for these phases can be used to decipher cooling through wide temperature ranges (e.g., Baughman et al, ; Flowers et al, ; Gautheron et al, ; Guenthner et al, ; Orme et al, ; Powell et al, ; Shuster et al, ). For example, zircon and titanite (U‐Th)/He (ZHe, THe) closure temperatures (T c ) can vary by up to 180°C owing to this effect (Guenthner et al, ; Baughman et al, ).…”