Connecting visual metamictization to radiation damage to expand applications of zircon (U-Th)/He thermochronometry

Armstrong, Emma M.; Ault, Alexis K.; Kaempfer, Jenna M.; Guenthner, William R.

doi:10.1016/j.chemgeo.2024.121949

Cited by 2 publications

(2 citation statements)

References 54 publications

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“…B1). Zircon grain clarity was initially considered because this characteristic correlates with radiation damage (e.g., Ault et al, 2018;Armstrong et al, 2024), which influences zircon He retentivity (and therefore the ZHe date) and zircon density (and therefore the estimated mass and eU values). Grain clarity thus can be useful information to record during grain selection and is retained in the twoaxis zircon GEM (Fig.…”

Section: Appendix B: Additional Sample and Methods Informationmentioning

confidence: 99%

“…3.2; Appendix A). Zircon grain clarity is known to correlate with radiation damage (e.g., Ault et al, 2018;Armstrong et al, 2024), which influences He retentivity and zircon density, making grain clarity useful information to record during grain selection. We include further discussion of grain clarity and a two-axis zircon GEM in Appendix B, but we do not discuss zircon clarity further in the main text as this parameter does not impact the geometric corrections and uncertainties (Table C2).…”

Section: Selecting a Morphologically Representative Zircon Crystal Su...mentioning

confidence: 99%

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The Geometric Correction Method for zircon (U–Th) ∕ He chronology: correcting systematic error and assigning uncertainties to alpha-ejection corrections and eU concentrations

Zeigler,

Baker,

Metcalf

et al. 2024

Geochronology

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Abstract. The conventional zircon (U–Th) / He (ZHe) method typically uses microscopy measurements of the dated grain together with the assumption that the zircon can be appropriately modeled as a geometrically perfect tetragonal or ellipsoidal prism in the calculation of volume (V), alpha-ejection correction (FT), equivalent spherical radius (RFT), effective uranium concentration (eU), and corrected (U–Th) / He date. Here, we develop a set of corrections for systematic error and determine uncertainties to be used in the calculation of the above parameters for zircon, using the same methodology as Zeigler et al. (2023) for apatite. Our approach involved acquiring both “2D” microscopy measurements and high-resolution “3D” nano-computed tomography (CT) data for a suite of 223 zircon grains from nine samples showcasing a wide range of morphology, size, age, and lithological source, calculating the V, FT, and RFT values for the 2D and 3D measurements and comparing the 2D vs. 3D results. We find that the values derived from the 2D microscopy data overestimate the true 3D V, FT, and RFT values for zircon, with one exception (V of ellipsoidal grains). Correction factors for this misestimation determined by regressing the 3D vs. 2D data range from 0.81–1.04 for V, 0.97–1.0 for FT, and 0.92–0.98 for RFT, depending on zircon geometry. Uncertainties (1σ) derived from the scatter of data around the regression line are 13 %–21 % for V, 5 %–1 % for FT, and 8 % for RFT, again depending on zircon morphologies. Like for apatite, the main control on the magnitude of the corrections and uncertainties is grain geometry, with grain size being a secondary control on FT uncertainty. Propagating these uncertainties into a real dataset (N=28 ZHe analyses) generates 1σ uncertainties of 12 %–21 % in eU and 3 %–7 % in the corrected ZHe date when both analytical and geometric uncertainties are included. Accounting for the geometric corrections and uncertainties is important for appropriately reporting, plotting, and interpreting ZHe data. For both zircon and apatite, the Geometric Correction Method is a practical and straightforward approach for calculating more accurate (U–Th) / He data and for including geometric uncertainty in eU and date uncertainties.

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Section: Appendix B: Additional Sample and Methods Informationmentioning

confidence: 99%

Section: Selecting a Morphologically Representative Zircon Crystal Su...mentioning

confidence: 99%

The Geometric Correction Method for zircon (U–Th) ∕ He chronology: correcting systematic error and assigning uncertainties to alpha-ejection corrections and eU concentrations

Zeigler,

Baker,

Metcalf

et al. 2024

Geochronology

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The daughter–parent plot: a tool for analyzing thermochronological data

Härtel,

Enkelmann

2024

Geochronology

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Abstract. Data plots of daughter against parent concentration (D–P plots) are a potential tool for analyzing low-temperature thermochronology, similar to isochron plots in radioisotopic geochronology. Their purposes are to visualize the main term of the radiometric age equation – the daughter–parent ratio – and to inspect the daughter–parent relationship for anomalies indicating influences of geological processes or analytical bias. The main advantages of the D–P plot over other data analysis tools are (1) its ability to detect systematic offsets in D and P concentrations, (2) its unambiguous representation of radiation-damage-dependent daughter retention, and (3) the possibility to analyze potential age outliers. Despite these benefits, the D–P plot is currently not used for analyzing low-temperature thermochronology data, e.g., from fission-track, (U–Th) / He, or zircon Raman dating. We present a simple, decision-tree-based classification for daughter–parent relationships based on the D–P plot that places a dataset into one of seven classes: linear relationship with zero intercept, cluster, linear relationship with systematic offset, nonlinear relationship, several age populations, scattered data, and inverse relationship. Assigning a class to a dataset enables choosing further data analysis steps and how to report a sample age, e.g., as a pooled, central, or isochron age or a range of ages. This classification scheme aims at facilitating thermochronological data analysis and making decisions more transparent. We demonstrate the proposed procedure by analyzing published datasets from a variety of geological settings and thermochronometers and introduce Incaplot, which is graphical user interface software that we developed to facilitate D–P plotting of thermochronology data.

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Connecting visual metamictization to radiation damage to expand applications of zircon (U-Th)/He thermochronometry

Cited by 2 publications

References 54 publications

The Geometric Correction Method for zircon (U–Th) ∕ He chronology: correcting systematic error and assigning uncertainties to alpha-ejection corrections and eU concentrations

The Geometric Correction Method for zircon (U–Th) ∕ He chronology: correcting systematic error and assigning uncertainties to alpha-ejection corrections and eU concentrations

The daughter–parent plot: a tool for analyzing thermochronological data

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