Short communication: Experimental factors affecting fission-track counts in apatite

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.

On etching, selection and measurement of confined fission tracks in apatite

“…It was conducted on induced tracks in four prism sections of Durango apatite etched for 20 s in 5.5 M HNO3 at 21 °C. Their nominal mean track lengths are ~16, ~14, ~12, and ~10 µm (Ketcham et al, 2015), and their transmitted-light track densities are between ~2.9 and ~1.9 10 6 cm -2 (Aslanian et al, 2022). The tracks were selected by scanning the samples in transmitted light using two conscious criteria: (1) the entire track could be captured in an image stack with a depth of 1.25 µm; (2) both ends of the track were distinct.…”

“…On the other, it presents a tool for investigating the factors controlling tE or the tE-distribution of the measured population. In the next sections we investigate the influences of the track density and length using Durango apatites annealed to nominal mean lengths of ~16, ~14, ~12 and ~10 µm (Ketcham et al, 2015;Aslanian et al, 2022).…”

Thermal history modeling techniques and interpretation strategies: Applications using HeFTy

“…Thermal history models bring all of this information together; they are the numerical tools we use to interpret thermochronologic data in the context of the temperature sensitivity of thermochronometers (i.e., kinetics derived from experimental observations) and independent knowledge or hypotheses about a study area's geologic history (Fox and Shuster, 2020). Advances in our understanding of additional factors that control individual cooling ages, such as radiation damage (e.g., Flowers et al, 2009) and crystal composition (Carlson et al, 1999) as well as fission-track etching and annealing (Ketcham and Tamer, 2021;Aslanian et al, 2022), have only added to the need for numerical tools to guide the assessment and interpretation of thermochronologic data sets.…”