Fission track etching and annealing phenomenon in phlogopite and their applications

Abstract

Systematic annealing experiments on fission tracks in phlogopite have been carried out under standard etching conditions to obtain the correction curve for the ages of phlogopite, which might have been lowered due to geological annealing of fossil fission tracks. Variation of fission track density with etching time at different annealing temperatures has been analysed in order to standardize the etching conditions. All the tracks in phlogopite are annealed by heating at 590 °C for 1 h. Extrapolation of experimental data suggests that a temperature of 215 °C would be required for 1 Ma to remove all the tracks. The corrected age of a phlogopite sample from Neyyur village, Kanya Kumari District, India, is 395 ± 20 Ma. The mean values of fission fragment range for induced 235U fission tracks, uranium concentration, activation energy, and an effective paleoisotherm for fission track clock in the Neyyur village phlogopite are 17.7 ± 2.0 μm, 3.12 × 10−9 g/g, 1.8 eV, and 150 °C, respectively.