Geochronological Techniques in Argon Isotope Analysis

Argon isotope geochronology exploits the decay of 40K to 40Ar to determine the timing of igneous, metamorphic and hydrothermal processes. Classical potassium–argon (K–Ar) dating measures the radiogenic 40Ar accumulated in mineral separates relative to potassium content, while the 40Ar/39Ar method refines this approach by irradiating samples to produce 39Ar from 39K, enabling internal standardisation and step‐heating experiments. Incremental heating or laser‐ablation protocols release argon in discrete temperature steps or spatial domains, thereby resolving complex thermal histories and distinguishing alteration or recoil effects. Advances in noble gas mass spectrometry, including multiple‐collector and high‐sensitivity configurations, have driven improvements in precision and detection limits, supporting single-grain and microanalytical studies. Rigorous calibration of decay constants, correction for atmospheric and excess argon, and integration with complementary chronometers such as U–Pb have enhanced the reliability and global applicability of argon‐based time scales, from volcanic stratigraphy to crustal fluid evolution.

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Geochronological Techniques in Argon Isotope Analysis publication trend

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Technical terms

K–Ar dating: Radioisotope dating method measuring radiogenic 40Ar produced by decay of 40K.

40Ar/39Ar dating: Incremental heating variant of K–Ar using neutron irradiation to convert 39K to 39Ar for internal standardisation.

Decay constant (λ): Probabilistic rate at which a radioactive nuclide decays, central to age calculations.

Excess argon: Non-radiogenic 40Ar incorporated into a sample that can lead to overestimation of radiometric ages.

Single-crystal analysis: Microanalytical approach measuring only one mineral grain to avoid averaging effects.

Noble gas mass spectrometer: Instrument that separates and quantifies argon isotopes with high precision.

References

1. 40Ar/39Ar age determination using ARGUS VI multiple-collector noble gas mass spectrometer: performance and its application to geosciences. Journal of Analytical Science and Technology (2015).
2. Production of 40Ar by an overlooked mode of 40K decay with implications for K-Ar geochronology. Geochronology (2020).
3. Large Amount of Excess Argon in Hydrothermal Quartz from the Vangtat Orogenic Gold Belt, Southern Laos: New In-Sight from K-Ar and Noble Gas Isotope Analyses. Minerals (2022).
4. Synchrotron Microanalytical Characterization and K/Ar Dating of the GL-O-1 Glauconite Reference Material at the Single Pellet Scale and Reassessment of the Age of Visually Mature Pellets. Minerals (2023).