OPTIMIZING THE ISOTHERMAL PLATEAU FISSION-TRACK DATING METHOD FOR VOLCANIC GLASS SHARDS

The dating of volcanic hydrated glass shards presents considerable dif ficulties. However, within recent years the fission-track method based on the isothermal plateau technique has been successfully applied to such glasses. Age estimates obtained by this means compare very well w ith those based on co-existing mineral phases using the K-Ar, Ar-40/Ar -39 and thermoluminescence techniques. Annealing studies of nuclear tr acks in the temperature range of 100-300-degrees-C have been made for various volcanic glass samples. The activation energy, E(a), for track annealing is determined in the frame of a model involving a unique va lue of E(a) for a given glass sample. These annealing studies suggest that the thermal stability of nuclear tracks in volcanic glasses is ma inly controlled by the SiO2/Al2O3 ratio.