- 1FIERCE, Goethe University Frankfurt, Frankfurt am Main, Germany (l.millonig@em.uni-frankfurt.de)
- 2Department of Earth Sciences, Boston University, United States
Garnet has an extensive pressure-temperature (P–T) stability field for a wide variety of rock compositions, and its compositional changes reflect changes during its prograde P–T evolution. The beauty of garnet petrochronometry is thus the ability to extract P–T and temporal (t) information from a single rock-forming mineral with relatively well-known thermodynamic properties.
While still in its infancy, U–Pb dating of garnet by LA–ICPMS is an evolving petrochronological tool with a vast potential and a plethora of possible applications. To assess its reliability and potential systematic differences in comparison with the well-established Sm-Nd ID-TIMS dating technique, we applied garnet U-Pb dating by LA-ICPMS to garnet specimen that were previously dated by Sm-Nd ID-TIMS. The investigated samples include Paleozoic to Cenozoic garnet samples from diverse geotectonic settings and bulk rock compositions, including blueschists, eclogites, metapelites, and meta-rodingites.
Our results indicate that the two dating techniques mostly yield similar results, demonstrating the accuracy of the in situ U-Pb method. We further demonstrate that garnet U-Pb dating by LA-ICPMS can resolve dates from thin garnets rims (<300 µm), which are too narrow to be dated by ID-TIMS. In the case of the meta-rodingite sample, we found that garnet veinlets formed during two events, which were not clearly resolved by ID-TIMS dating. These spatial resolution advantages of the LA-ICPMS technique are contrasted, however, by generally less precise garnet dates compared to the ID-TIMS data. Furthermore, in situ U-Pb dating can be rendered unfeasible mainly by two factors: (1) the presence of and contamination by (inherited) U-rich inclusions (e.g. zircon and monazite); (2) garnet contains more Pb than U, thereby severely limiting the spread in 238U/206Pb which produces significant uncertainties and geologically meaningless dates.
How to cite: Millonig, L. J., Beranoaguirre, A., Albert, R., Marschall, H., Baxter, E., and Gerdes, A.: Accuracy of garnet U–Pb LA–ICPMS compared to Sm-Nd TIMS dating, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19672, https://doi.org/10.5194/egusphere-egu25-19672, 2025.