Garnet Geochronology: Timekeeper of Tectonometamorphic Processes

Garnet’s potential as a chronometer of tectonometamorphic processes and conditions was fi rst recognized over 30 years ago. The Sm–Nd and Lu–Hf systems have since emerged as the most effective chronometers, permitting age precision of better than ±1 My, even on tiny samples such as concentric growth zones within individual crystals. New, robust analytical methods mitigate the effects of ubiquitous mineral inclusions, improving the precision and accuracy of garnet dates. Important differences between Sm– Nd and Lu–Hf with respect to partitioning, diffusivity, contaminant phases, and isotopic analysis make these two systems powerfully complementary.