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<p>The <sup>40</sup>Ar/<sup>39</sup>Ar dating method holds particular significance for determining the age of basic rocks. However, the presence of extraneous argon (<sup>40</sup>Ar<sub>E</sub>) in some samples generates complex <sup>40</sup>Ar/<sup>39</sup>Ar age spectra, compromising the technique’s utility in modern geochronology. This investigation focuses on deciphering the occurrence of <sup>40</sup>Ar<sub>E</sub> within a diabase and proposes strategies to mitigate its influence. Our results reveal distinct age patterns: separated feldspar yields a well-defined plateau age of 48.73 ± 0.07 (0.12) [2.06] Ma (2σ, MSWD = 0.86, <i>P</i> = 62%), while whole-rock analyses produce saddle-shaped age spectra. Through integration of EPMA major element data, K/Ca ratios from <sup>40</sup>Ar/<sup>39</sup>Ar results, and TIMA-derived mineral proportions, we identify metamorphosed amphibole as the primary host of <sup>40</sup>Ar<sub>E</sub> in this study. Thus, separated components containing metamorphosed amphiboles should be excluded as suitable targets for <sup>40</sup>Ar/<sup>39</sup>Ar geochronology. These findings provide critical guidance for sample selection and interpretation in basic rocks.</p>

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Excess 40Ar retention in metamorphosed amphibole complicates 40Ar/39Ar geochronological interpretation of diabase

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月27日

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  • Wan-Feng Zhang,
  • Jun-Jie Wang,
  • Jian-Lin Chen,
  • De-Wen Zheng,
  • Lin Ma,
  • Ming Xiao,
  • Yu-Lian Zhang,
  • Ying-De Jiang,
  • Yi-Gang Xu

摘要

The 40Ar/39Ar dating method holds particular significance for determining the age of basic rocks. However, the presence of extraneous argon (40ArE) in some samples generates complex 40Ar/39Ar age spectra, compromising the technique’s utility in modern geochronology. This investigation focuses on deciphering the occurrence of 40ArE within a diabase and proposes strategies to mitigate its influence. Our results reveal distinct age patterns: separated feldspar yields a well-defined plateau age of 48.73 ± 0.07 (0.12) [2.06] Ma (2σ, MSWD = 0.86, P = 62%), while whole-rock analyses produce saddle-shaped age spectra. Through integration of EPMA major element data, K/Ca ratios from 40Ar/39Ar results, and TIMA-derived mineral proportions, we identify metamorphosed amphibole as the primary host of 40ArE in this study. Thus, separated components containing metamorphosed amphiboles should be excluded as suitable targets for 40Ar/39Ar geochronology. These findings provide critical guidance for sample selection and interpretation in basic rocks.