The timing and processes of ductile deformation and metasomatism can be documented using apatite petrochronology. We integrated microstructural, U-Pb, and geochemical analyses of apatite grains from an exhumed mylonitic shear zone in the St. Barthélémy Massif, Pyrenees, France, to understand how deformation and metasomatism are recorded by U-Pb dates and geochemical patterns. Electron backscatter diffraction (EBSD) analyses documents crystal plastic deformation characterized by low-angle boundaries (<5°) associated with dislocation creep and evidence of multiple slip systems. Laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb maps indicate that dates in deformed grains reflect, and are governed by, low-angle dislocation boundaries. Apatite rare earth element (REE) and U-Pb behavior is decoupled in high-grade gneiss samples, suggesting REEs record higher-temperature processes than U-Pb isotopic systems. Apatite from (ultra)mylonitic portions of the shear zone showed evidence of metasomatism, and the youngest dates constrain the age of metasomatism. Collectively, these results demonstrate that crystal plastic microstructures and fluid interactions can markedly change apatite isotopic signatures, making single-grain apatite petrochronology a powerful tool for dating and characterizing the latest major deformation and/or fluid events, which are often not captured by higher-temperature chronometers.

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单粒磷灰石岩石年代学记录的变形和交代作用

可使用磷灰石岩石年代学记录延性变形和交代作用的时间和过程。我们整合了来自法国比利牛斯山脉圣巴泰勒米地块的挖掘出的糜棱岩剪切带的磷灰石晶粒的微观结构、U-Pb 和地球化学分析，以了解 U-Pb 日期和地球化学模式如何记录变形和交代作用。电子背散射衍射 (EBSD) 分析记录了以与位错蠕变相关的低角度边界 (<5°) 为特征的晶体塑性变形和多个滑移系统的证据。激光烧蚀电感耦合等离子体质谱 (LA-ICP-MS) U-Pb 图表明变形晶粒中的日期反映了低角度位错边界并受其支配。磷灰石稀土元素 (REE) 和 U-Pb 行为在高品位片麻岩样品中是解耦的，这表明 REE 记录了比 U-Pb 同位素系统更高的温度过程。来自剪切带（超）糜棱部分的磷灰石显示出交代作用的证据，并且最年轻的日期限制了交代作用的年龄。总的来说，这些结果表明，晶体塑性微结构和流体相互作用可以显着改变磷灰石同位素特征，使单粒磷灰石岩石年代学成为测定和表征最新主要变形和/或流体事件的有力工具，这些事件通常无法被更高的-温度计时器。最年轻的日期限制了交代的年龄。总的来说，这些结果表明，晶体塑性微结构和流体相互作用可以显着改变磷灰石同位素特征，使单粒磷灰石岩石年代学成为测定和表征最新主要变形和/或流体事件的有力工具，这些事件通常无法被更高的-温度计时器。最年轻的日期限制了交代的年龄。总的来说，这些结果表明，晶体塑性微结构和流体相互作用可以显着改变磷灰石同位素特征，使单粒磷灰石岩石年代学成为测定和表征最新主要变形和/或流体事件的有力工具，这些事件通常无法被更高的-温度计时器。