He diffusion kinetics in highly radiation-damaged zircon: Insights from step-heating experiments for the (U-Th)/He system

R.O. Sigat, W. Guenthner, L. Nasdala

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Abstract

The zircon (U-Th)/He thermochronometer has been extensively used to study thermal histories in diverse geologic settings. The accuracy of thermal and geologic interpretations relies on a robust understanding of ⁴He diffusion. Guenthner et al. (2013) parametrized the relationship between ⁴He diffusion kinetics and radiation damage, which is implemented in the zircon radiation damage accumulation and annealing model (ZRDAAM). This model represented an important step towards a more comprehensive understanding of ⁴He diffusion; however, lingering questions and avenues for further improvements remain. The present work aims to expand upon and complement previously published diffusion kinetics with new step-heating experiments on high-damage zircon crystals above the rollover point from decreasing to increasing diffusivities (,1–2 × 10¹⁸ α/g). Accurate characterization of the damage-diffusivity relationship at and above the rollover point is crucial for the continued use of ZRDAAM in deep-time (>1 Ga) thermal history applications. We prepared c-axis oriented, thinly sliced, Sri Lankan zircons for step-heating experiments consisting of specimens GZ8 (2.53 × 10¹⁸ α/g), G168 (2.92 × 10¹⁸ α/g), GZ5 (3.97 × 10¹⁸ α/g), and G4 (4.70 × 10¹⁸ α/g). We report preliminary kinetic parameter values of Eₐ = 120.23 ± 0.71 kJ/mol (1σ) and D₀ = (2.20 ± 0.31) × 10⁻³ cm²/s (1σ) for G168, which agree with observed Eₐ and D₀ data trends from previously published experimental datasets. Although further work needs to be done, results for specimen G168 present convincing evidence for the robustness of the diffusion kinetics of ZRDAAM for high radiation damage levels.
Original languageEnglish
Title of host publicationThermo2023
Subtitle of host publication18th International Conference on Thermochronology, Riva del Garda, Italy, September 2023. Abstract volume
Pages163
Number of pages1
Publication statusPublished - Sep 2023

Austrian Fields of Science 2012

  • 105113 Crystallography
  • 105116 Mineralogy
  • 104026 Spectroscopy

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