Short-term annealing characteristics of spontaneous fission tracks in zircon: A qualitative description

Thermal annealing behavior of fission tracks (FT) has not yet been documented under short-term (< 4 min) heating condition. We performed a new series of 17 laboratory heating experiments on spontaneous FTs in zircon at 550–910 °C for ∼4, 10 and 100 s under strict controls of time and temperature using a graphite furnace. FTs were almost completely annealed at 912 °C for 3.9 s, at 858 °C for 10.4 s and at 805 °C for 100.6 s. These results suggest that FTs in zircon are totally annealed at time–temperature conditions of ordinary pseudotachylyte formation (i.e. at 1000 °C for 5 s). The measured FT lengths in ∼4 and 10 s heating runs are shorter than that predicted by previous annealing kinetic models, suggesting a more rapid annealing therein. The component of short tracks in these samples increases suddenly as the annealing proceeds, which has not been observed for longer heating runs including the results of previous studies. Such rapid shortening for ∼4 and 10 s heating is caused by earlier emergence of the annealing process of segmentation.