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

• Published in: Geochronology
• Main Authors: D. R. Issler, K. T. McDannell, P. B. O'Sullivan, L. S. Lane
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Geology; QE1-996.5; Stratigraphy; QE640-699; Yukon; Northwest Territories; Canada
• Online Access: https://doi.org/10.5194/gchron-4-373-2022; https://doaj.org/article/6a227817f0254de398fd734da1d15839

Compositionally dependent apatite fission track (AFT) annealing is a common but underappreciated cause for AFT age dispersion in sedimentary samples. We present an interpretation and modelling strategy for samples with variable apatite composition 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 northern Yukon, Canada, both with complicated geological histories and long residence times in the AFT partial annealing zone. Effective Cl values (eCl; converted from r mr0 values) derived from detailed apatite elemental data are used to define AFT statistical kinetic populations with significantly different total annealing temperatures ( ∼110 –185 ∘ 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 of Cl content or D par . Elemental analyses and measured D par for Phanerozoic samples from Yukon and the Northwest Territories confirm that D par 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 ...