A natural long‐term annealing experiment for the zircon fission track system in the Songpan‐Garzê flysch, China. (16th May 2019) - Rahn, Meinert
Abstract: Application of the zircon fission track (FT) method to derive reliable cooling histories requires that rocks have undergone temperatures sufficient to reach full resetting prior to cooling. Zircons commonly show significant variation in accumulated radiation damage and therefore FT annealing behaviour. Twenty‐eight samples of mainly anchizonal to lowermost greenschist facies Triassic sandstones from the Songpan‐Garzê flysch, China, were evaluated for their FT annealing status. Literature data suggest a heating period in the range of 100 myr duration. Our results define a temperature range for partial FT annealing of 270–350°C (based on illite crystallinity data), higher than the proposed range for radiation‐damaged zircons. We suggest that the long residence at high temperature has led to annealing of relevant parts of radiation damage along with FT annealing, so that even for long durations of FT annealing, full resetting requires temperatures in the range of greenschist facies conditions typical for zero‐damage zircons.