In-situ Lu-Hf for provenance analysis – a methodological perspective

The development of in-situ Lu-Hf LA–ICP–MS/MS geochronology has opened avenues to dating garnet, apatite, xenotime, calcite and epidote-group minerals. Of these phases, garnet and apatite are particularly relevant to provenance analysis, as both can be dated in situ by the U–Pb, Sm–Nd and Lu–Hf systems, are often present in sediments, and retain geochronological as well as geochemical information during erosion, transport and sedimentation. Garnet and apatite also have the benefit of forming in different geological settings to minerals more widely used in provenance analysis, such as zircon. Zircon usually forms during high-temperature processes such as anatexis and magmatic crystallisation, and has a bias towards more felsic rock compositions. Conversely, garnet is a dominantly metamorphic mineral, and usually retains information about the prograde (and sub-anatectic) history of metamorphic rocks, but may also form in hydrothermal settings, and is stable across a wide variety of lithological compositions. Apatite also forms in a wide variety of rock lithologies during metamorphism and magmatism, and therefore can represent more intermediate and mafic magmatic events which are not sampled by zircon. In situ Lu–Hf geochronology therefore provides an excellent tool to understand the timing and conditions of mountain building and magmatic events from the detrital record, but not without methodological and geological caveats and limitations. The application of the method itself, data handling and analytical interpretations will be presented and discussed.