Preprints
https://doi.org/10.5194/gchron-2021-22
https://doi.org/10.5194/gchron-2021-22

  02 Aug 2021

02 Aug 2021

Review status: this preprint is currently under review for the journal GChron.

Simulating sedimentary burial cycles – Part 2: Elemental-based multikinetic apatite fission-track interpretation and modelling techniques illustrated using examples from northern Yukon

Dale R. Issler1, Kalin T. McDannell2, Paul B. O'Sullivan3, and Larry S. Lane1 Dale R. Issler et al.
  • 1Natural Resources Canada, Geological Survey of Canada, Calgary, AB, T2L 2A7, Canada
  • 2Department of Earth Sciences, Dartmouth College, Hanover NH, 03755, United States
  • 3GeoSep Services, Moscow, ID, 83843, United States

Abstract. Compositionally dependent apatite fission track (AFT) annealing is a common but underappreciated cause for age dispersion in detrital AFT samples. We present an interpretation and modelling strategy that exploits multikinetic AFT annealing to obtain thermal histories that can provide more detail and better resolution compared to conventional methods. We illustrate our method using a Permian and a Devonian sample from the Yukon, Canada, both with complicated geological histories and long residence times in the AFT partial annealing zone. Effective Cl values (eCl; converted from rmr0 values), derived from detailed apatite elemental data, are used to define AFT statistical kinetic populations with significantly different total annealing temperatures (~110–245 °C) and ages that agree closely with the results of age mixture modelling. These AFT populations are well-resolved using eCl values but exhibit significant overlap with respect to the conventional parameters, Cl content or Dpar. Elemental analyses and measured Dpar for Phanerozoic samples from the Yukon and Northwest Territories confirm that Dpar has low precision and that Cl content alone cannot account for the compositional and associated kinetic variability observed in natural samples. An inverse multikinetic AFT model, AFTINV, is used to obtain thermal history information by simultaneously modelling multiple kinetic populations as distinct thermochronometers with different temperature sensitivities. A nondirected Monte Carlo scheme generates a set of statistically acceptable solutions at the 0.05 significance level and then these solutions are updated to the 0.5 level using a controlled random search (CRS) learning algorithm. The smoother, closer-fitting CRS solutions allow for a more consistent assessment of the eCl values and thermal history styles that are needed to satisfy the AFT data. The high-quality Devonian sample (39 single grain ages and 202 track lengths) has two kinetic populations that require three cycles of heating and cooling (each subsequent event of lower intensity) to obtain close-fitting solutions. The younger and more westerly Permian sample with three kinetic populations only records the latter two heating events. These results are compatible with known stratigraphic and thermal maturity constraints and the QTQt software produces similar results. Model results for these and other samples suggest that elemental-derived eCl values are accurate within the range, 0–0.25 apfu (rmr0 values of 0.73–0.84), which encompasses most of the data from annealing experiments. Outside of this range, eCl values for more exotic compositions may require adjustment relative to better constrained apatite compositions when trying to fit multiple kinetic populations. Our results for natural and synthetic samples suggest that an element-based multikinetic approach has great potential to increase the temperature range and resolution of thermal histories dramatically relative to conventional AFT thermochronology.

Dale R. Issler et al.

Status: open (until 20 Oct 2021)

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Dale R. Issler et al.

Data sets

A multikinetic approach to apatite fission-track thermal modelling using elemental data: data and model results for a Permian and Devonian sample from northern Yukon Issler, D. R., McDannell, K. T., Lane, L. S., O’Sullivan, P. B. and Neill, O. K. https://doi.org/10.4095/328844

Dale R. Issler et al.

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Short summary
Phanerozoic sedimentary rocks of northern Canada have compositionally heterogeneous detrital apatite with high age dispersion caused by differential thermal annealing. Discrete AFT kinetic populations with variable annealing temperatures are defined using elemental data but are poorly resolved using conventional parameters (Dpar and Cl). Inverse thermal modelling of samples from northern Yukon reveals a complicated record of multiple heating-cooling cycles consistent with geological constraints.