Abstract Micas are among the most commonly-dated minerals by the 40Ar/39Ar technique to determine the crystallization or cooling ages of rocks. Interpretation of the geological significance of these ages is largely dependent on understanding how 40Ar* (radiogenic argon) can be retained or released from the mineral during the thermal history of a terrane. The interlayer ionic porosity (Zi) model, serving as a measure of a mineral’s atomic packing density, has been proposed in an attempt to understand and explain the diffusive behaviour of argon (Ar) and its retention in micas. We tested this model by dating micas from several outcrops using the 40Ar/39Ar and Rb/Sr techniques along a ∼ 5.2 km transect in the Frontenac terrane, Grenville Province, Ontario. This transect is ideal because: (a) the rocks in this small area experienced the same geologic history, and (b) there are a variety of lithologies containing trioctahedral and dioctahedral micas with different chemical compositions. Our results show that trioctahedral and dioctahedral micas yielded 40Ar/39Ar plateau ages that differ by ∼150 Ma. Significantly, although both Mg# and F# correlate with Zi, as predicted by the model, there is no correlation between Mg#, F#, and Zi and the age of the micas in similar lithologies. This suggests that the interlayer ionic porosity model, in itself, may not be suitable for explaining mechanisms of Ar mobility in micas alone. Instead, both internal (chemical composition, bulk rock properties) and external (fluid composition, open/closed-system behaviour) factors that may influence Ar retentivity in micas should be more broadly considered in order to elucidate the significance of their 40Ar/39Ar ages.

中文翻译：

---

层间离子孔隙率模型测试作为三八面体云母中氩扩散率的量度

摘要 云母是通过 40Ar/39Ar 技术确定岩石结晶或冷却年龄最常用的矿物之一。对这些年龄的地质意义的解释在很大程度上取决于对 40Ar*（放射性氩）如何在地体的热历史过程中从矿物中保留或释放的理解。层间离子孔隙率 (Zi) 模型作为矿物原子堆积密度的量度，已被提出以试图理解和解释氩 (Ar) 的扩散行为及其在云母中的保留。我们通过使用 40Ar/39Ar 和 Rb/Sr 技术沿着安大略省格伦维尔省 Frontenac 地体的约 5.2 公里横断面对来自几个露头的云母进行测年来测试该模型。该断面是理想的，因为：(a) 这个小区域的岩石经历了相同的地质历史，以及 (b) 存在多种岩性，含有不同化学成分的三八面体和二八面体云母。我们的结果表明，三八面体和双八面体云母产生了 40Ar/39Ar 平台年龄，相差约 150 Ma。值得注意的是，尽管 Mg# 和 F# 都与 Zi 相关，正如模型所预测的那样，但 Mg#、F# 和 Zi 与类似岩性中云母的年龄之间没有相关性。这表明层间离子孔隙率模型本身可能不适合单独解释云母中 Ar 迁移率的机制。相反，内部（化学成分、大块岩石特性）和外部（流体成分、