Exploring the potential of apatite Lu-Hf dating of igneous processes in mafic systems

• Applicant: Dr. Johannes Pohlner
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 569254776

Mafic rocks play a crucial role in deciphering tectonic and ore-forming processes and for finding the causes of past global climate crises, but dating their igneous crystallization with conventional methods (e.g., U-Pb zircon or Ar-Ar) is often difficult or impossible. By contrast, apatite is usually abundant in such rocks, and recent studies testify its high potential to preserve Lu-Hf age information during secondary processes. The Lu-Hf apatite method proved itself reliable for Precambrian rocks, for which it can be directly used to address large-scale geologic problems. Therefore, the principal target of the project is the largest anorthosite complex in the world, the Mesorpoterozoic Kunene Complex (Angola/Namibia). Previous data led to the controversial hypothesis that its magmatic assembly took >120 Myr, which will be tested here. A thorough apatite petrochronology in comparison with previously published baddeleyite/zircon data will enable the compilation of a comprehensive geochronological barcode leading to detailed insights about the duration, rhythm and mechanisms of anorthosite formation. Application of the Lu-Hf method on apatite in younger or deformed/metamorphosed rocks faces challenges and still requires validation. A smaller occurrence of Cretaceous mafic sills in the Silesian Basin (Poland/Czech Republic) will serve to explore the potential of the method for Phanerozoic rocks. Furthermore, metagabbros from the Münchberg Massif (Germany) that show all transitions from weakly metamorphosed gabbros to strongly deformed amphibolites are targeted to investigate the behavior of the apatite Lu-Hf system upon progressive metamorphism and deformation. Moreover, the first quantitative comparison of the advantages of the in-situ variant (faster and with high spatial resolution) and the solution-based variant (higher precision) of Lu-Hf apatite dating will be performed by applying both methods to the same samples. To attain the project objectives, Lu-Hf dating will be accompanied by thorough petrographic characterization, U-Pb dating and mineral chemical and Nd-Hf isotopic studies. Besides new insights into the evolution of the investigated geological units, the outcomes of the project would help future studies in optimizing their analytical strategies, especially to identify opportunities for dating rocks or processes that were previously thought undateable.

• DFG Programme: Research Grants