Deformation and metasomatism recorded by single-grain apatite petrochronology

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