Statistical modelling of annealing kinetics of fission tracks in zircon; Reassessment of laboratory experiments

We remodel the annealing kinetics of fission tracks (FTs) in zircon to fit data from 43 laboratory experiments in three earlier publications using spontaneous FT lengths in zircon from the Nisatai Dacite. Heating temperature and time are in the ranges of 350–912 °C and 10− 3–104 h, respectively. The data sets illustrate a transition in annealing process at a certain temperature zone. In order to express the annealing behavior involving the possible transitional process with improved goodness of fit, two types of models are constructed; the hybrid-linear model that consists of the fanning-linear model at high temperature and the parallel-linear model at low temperature, connected with a transitional temperature zone, and the parallel-curvilinear model that approximates smoothly the transition in the annealing process. The validity of the extrapolation of the model to geological time scale is confirmed by comparison with some deep borehole core data. The length estimates by the hybrid-linear model agree well with the borehole data, whilst the estimates by the parallel-curvilinear model show a significant disagreement with highly annealed borehole samples although this model provides good agreement with the experimental data. For the hybrid-linear model, estimates of the partial annealing zone corresponding to isothermal heating for 106 and 107 years are 281–352 °C and 262–330 °C where the top and bottom of the partial annealing zone are defined by the mean length reduction ratio of 0.4 and 0.8, respectively.