Toward FAIR Fission-Track Data Multi-Approach Reassessment of the Sudbury Drill Core

Thermo2025 Poster download HERE

Correspondence to: Ling Chung (ling.chung@unimelb.edu.au)

1. Motivations

Recent studies reveal external detector method (EDM) derived AFT ages are often younger than revised or reanalysed LA-ICP-MS fission-track (LAFT) data. Such discrepancies occur not only between laboratories but also among analysts within the same group, using the same mineral separates. Examples include the Gawler Craton and southeast Australia, where early AFT datasets obtained by the external detector method (EDM) returned younger ages compared to more recent LA-ICP-MS fission-track (LAFT) results [1-4].

This conflict is also evident from LAFT analyses of samples from the 3440-m-deep Sudbury Igneous Complex (SIC) drill hole, previously dated using the EDM approach [5]. These samples were subsequently examined as a case study to investigate the underlying causes of age discrepancies. The resulting insights motivated the present study, which aims to systematically evaluate potential sources of such inconsistencies.

2. Experimental process

Archived Sudbury EDM mounts were re-analysed by analyst 2 (An2) at the same laboratory (Lab1) using image-based EDM (IEDM) and LAFT. A pilot sample and its high-resolution overview map were then transferred to Lab2 for EDM analysis by An3, who marked the grains analysed directly on the overview map. The mount was subsequently returned to Lab1 for coordinated LAFT analysis of those grains. Overview maps thus enabled cross-lab grain documentation and direct LAFT–EDM comparison.

3, Preliminary results and investigations

·     All AFT ages obtained here are systematically older than those of the original study.

·     IEDM and LAFT ages from An2, and LAFT ages from An3, are concordant within uncertainty.

·     EDM ages from An3 are younger than their paired LAFT ages.

To identify the causes, we evaluated factors critical to AFT age determination: area selection, spontaneous (ρ_s), induced (ρ_i), and dosimeter (ρ_d) track densities, zeta calibration (ζ), and uranium concentration estimates. Area selection ranges were comparable among analysts. However, ρ_s values from An1 were lower than those of An2 and An3, while ρ_d values from An3 were lower than those of An1 and An2 (with An2 slightly higher than An1). These patterns suggest that younger ages in the original study may reflect undercounting of spontaneous tracks by An1, while divergence between An2 and An3 is linked to difference in ρ_d estimates with ζ differences also contributing.

4. Implications

This study provides the first robust inter-analyst evaluation of EDM and LAFT datasets on identical mounts, advancing beyond earlier EDM–LAFT comparisons that were typically limited to a single analyst and focused primarily on uranium concentration estimates (e.g., U = ρ_i / ρ_d × U_std) [6,7]. The results demonstrate methodological variability between analysts, highlighting the need to standardise measurement protocols, the advantages of image-based documentation, and the importance of transparent, accessible reporting to support FAIR (Findable, Accessible, Interoperable, and Reusable) fission-track data [8].

References

[1] Boone, S.C. et al. (2016). Australian Journal of Earth Sciences, 63(3), pp.315-331.

[2] Glorie, S. et al. (2019). Ore Geology Reviews, 115, p.103193.

[3] McMillan, M. et al. (2019). Terra Nova, 32(2), pp.109–121.

[4] Gleadow, A.J. et al. (2002). Tectonophysics, 349(1-4), pp.5-21.

[5] Lorencak, M. et al. (2004) Earth and Planetary Science Letters, 227(1-2), 87-104.

[6] Hasebe, N. et al. (2004). Chemical Geology, 207, 135-145.

[7] Seiler, C. et al. (2023). Chemical Geology, 635, 121623.

[8] Kohn, B. P. et al. (2024). GSA Bulletin, 136(9-10), 3891-3920.