Deciphering apatite (U-Th-Sm)/He age dispersion: a multi-parameter approach

• Applicant: Dr. Birk Härtel
• Subject Area: Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 531299808

Apatite (U-Th-Sm)/He (AHe) dating provides age information for rocks in the 40–80 °C temperature range, ideal for investigating the thermal history in the upper 1-5 km of the continental crust. However, the often-observed intra-sample age dispersion, the variation of single-grain ages beyond analytical uncertainty, complicates the interpretation of AHe data. The dispersion results from the interplay of the sample’s thermal history and the variation in apatite-grain properties such as zoning, chemical composition, or crystallinity. In sediments, the dispersion is enhanced by inheritance of helium from the pre-depositional histories of varying source rocks. As current models fall short of explaining all the age variation, understanding its causes is one of the major challenges in apatite thermochronology. My aim for this research project is toe investigate thes causes by combining AHe dating with several grain-property measurements and analyze their relationship to the age variation. The conventional, whole-grain AHe technique is suboptimal for this prospect: it only allows the analysis of a small number of grains and is limited with regards to grain-property measurements. In contrast, the newly developed laser-ablation AHe technique (LA-AHe) has the potential for elucidating the causes of age dispersion because it enables the efficient dating of hundreds of grains while simultaneously measuring grain properties. The project will involve dating of bedrock samples to quantify the differences between the whole-grain and LA-AHe techniques, and to investigate how different thermal histories affect the grain-property-age relationship. I will also analyze sedimentary samples to study the effects of pre-depositional history. I expect these findings to provide a new foundation for interpreting dispersed AHe data, improve the geological application of AHe dating, and guide the way for investigating age dispersion in other dating methods.

• DFG Programme: WBP Fellowship
• International Connection: Canada
• Host: Professorin Dr. Eva Enkelmann