Thermal annealing kinetics of induced fission tracks in ZAD zircon from the Serra Geral Volcanic Complex, Brazil

Abstract

This study investigates the thermal annealing kinetics of induced fission tracks in ZAD zircon from the Serra Geral Volcanic Complex, Brazil, and compares results with previously studied ZPC zircon. Both samples underwent identical pre-annealing treatment (1100 °C for 1 h) to remove fossil fission tracks before neutron irradiation and heating experiments at temperatures between 500 and 800 °C for durations of 1–100 h. Comprehensive statistical analysis, including Kolmogorov–Smirnov tests and effect size calculations, confirmed that observed differences between samples reflect genuine material properties rather than measurement bias. ZAD exhibited significantly higher annealing rates and lower activation energy (62 ± 14 kcal/mol) compared to ZPC (80 ± 20 kcal/mol), despite both samples undergoing identical laboratory procedures. This differential behavior is attributed to ZAD’s 20% higher accumulated α-recoil damage (3.34 × 10¹⁶ vs. 2.67 × 10¹⁶ decays/g), which persists as residual damage even after pre-annealing treatment. Calculations of displacements per atom (dpa) further quantified this difference (1.07 × 10⁻³ for ZAD vs. 8.5 × ⁻⁴ for ZPC). The study demonstrates how radiation damage accumulated over different timescales (134 Ma for ZAD vs. 80 Ma for ZPC) creates distinct microstructural defect patterns that significantly influence fission track annealing kinetics, with important implications for zircon thermochronology interpretations and geological thermal history reconstruction.