Etching and annealing studies of fission tracks in chlorite and their applications in dating

Abstract

Etching characteristics of fission fragment tracks in chlorite from central Sierra Nevada Batholith, California, USA, are studied using HF as the track etchant. Systematic annealing experiments are carried out in order to obtain correction factor for the age of chlorite, which has suffered annealing during its geological history. Complete erasure of fission tracks in chlorite occurs for 4 hrs annealing at 600°C. Extrapolation of experimental annealing data suggests that a temperature of 155°C would remove all fission tracks in chlorite in 1 Ma. The annealing correction of 15% determined by the age-plateau method gives the corrected age as 161±30 Ma for this mineral. Uranium content in chlorite is quite low (∼0.315 ppm). The mean value of activation energy is 1.6 eV.