Fission track dating of volcanic glasses and the thermal history of rocks

Abstract

The fission track method was applied to get information about a sample's thermal history, using Permian pitch-stone glasses from South Tyrol as an example. The fission track ages obtained are lowered due to thermal annealing. They range between 61 m.y. and 186 m.y. Going from the South to the North, the ages decrease. Size studies of the fossil fission tracks reveal that the measured ages are mixed ages, composed of a thermally unaffected and a thermally affected age. The latter part of the mixed ages can be corrected. The corrected fission track ages converge to a mean age of 256 m.y. The thermally unaffected ages date the end of the last thermal event. They range between 21 m.y. and 149 m.y. The measured and the corrected fission track ages as well as the thermal history of the pitchstones are discussed. The results are a typical example how to use fission tracks as geological thermometer.