Fission tracks simulated by swift heavy ions at crustal pressures and temperatures

Using a new experimental approach, fission-track formation has been simulated, for the first time, under crustal conditions by exposing natural zircon, at a pressure of 7.5 kbar and a temperature of 250 °C, to a beam of relativistic heavy ions. The latent tracks were investigated using high-resolution transmission electron microscopy, and the diameters of several hundred tracks were measured. The mean values (± σ) of the track diameters were 5.2 ± 0.5 nm and 5.4 ± 0.4 nm for zircon at ambient and elevated pressure-temperature, respectively. Based on the number of measurements, this represents a statistically significant difference between the tracks at ambient vs. high-pressure/temperature conditions. The slightly larger size of the tracks at elevated pressure can be understood in terms of the increased efficiency of the damage process in a strained crystal lattice. This slight variation in track diameter (~ 0.2 nm) at high pressure probably will not affect the dimensions of etched tracks.