Abstract
Abstract. The tools for interpreting fission-track data are evolving apace, but, even so, the outcomes cannot be better than the data. Recent studies showed that track etching and observation affect confined-track length measurements. We investigated the effects of grain orientation, polishing, etching and observation on fission-track counts in apatite. Our findings throw light on the phenomena that affect the track counts and hence the sample ages, whilst raising the question: what counts as an etched surface track? This is pertinent to manual and automatic track counts and to designing training strategies for neural networks. Counting prism faces and using the ζ calibration for age calculation are assumed to deal with most etching- and counting-related factors. However, prism faces are not unproblematic for counting, and other surface orientations are not unusable. Our results suggest that a reinvestigation of the etching properties of different apatite faces could increase the range useful for dating and lift a significant restriction for provenance studies.
Highlights
Fission-track dating and temperature–time path modeling are much used thermochronological tools for geological research
We submit this contribution from a concern that, while the tools for interpreting fission-track data are evolving, the calculated ages, age components and thermal histories are only as good as the track counts and the measured track lengths
Recent studies that have taken up the twin issues of etching and observation confirm that both have an effect on confined-track lengths (Jonckheere et al, 2007, 2017; Tamer et al, 2019; Tamer and Ketcham, 2020; Aslanian et al, 2021; Ketcham and Tamer, 2021)
Summary
Fission-track dating and temperature–time path modeling are much used thermochronological tools for geological research. The fission-track method rests on counting and measuring the lattice damage trails caused by uranium fission. Latent fission tracks in apatite are ∼ 20 μm long (Bhandari et al, 1971; Jonckheere, 2003) and ∼ 10 nm wide (Paul and Fitzgerald, 1992; Paul, 1993; Li et al, 2011, 2012, 2014), too thin to observe with an optical microscope. The polished grain mounts are etched to make them visible. It is often taken for granted that factors related to etching and counting are inconsequential, e.g., that counting losses
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