Abstract
Systematic annealing experiments of fission tracks were carried out with three hornblendes from a granodiorite, a schist and an andesite. Almost all tracks disappeared in 2 hours at 550°C for hornblende from a granodiorite and at 650°C for those from a schist and an andesite. Extrapolation of experimentally determined temperatures suggests that fission tracks in hornblende become undetected, if heated above 300 ± 50°C for the period between 102 and 106 years.
