SPEED DATING!: ADVICE ON SAMPLING AND APPLICATIONS FOR (U-TH)/HE THERMOCHRONOMETRY

A transformative advance in Earth science is development of thermochronometry to quantify the thermal evolution of rocks through time. Low-temperature thermochronometry – specifically (U-Th)/He dating – is now a cornerstone of geoscience investigations documenting the timing and tempo of thermal processes, including mountain building, landscape evolution and erosion, fault slip, and mineralization. (U-Th)/He thermochronometry exploits the natural decay of isotopes of uranium (U) and thorium (Th), associated alpha particle (He) production, and temperature-sensitive He diffusion (closure temperature) through the crystal. Target phases include apatite, zircon, titanite, hematite, magnetite, goethite, perovskite, and monazite, with collective closure temperatures spanning ~25-300 °C. These tools are well suited to reconstruct the thermal imprint of processes operative in the upper ~10 km of Earth’s crust.

Application of (U-Th)/He thermochronometry to address outstanding Earth science problems requires consideration of the motivating science questions, as well as appropriate sampling strategy, careful sample processing, and detailed target aliquot selection and characterization. Accurate interpretation of (U-Th)/He results, data patterns, and conversion of dates to rates of processes integrates complementary geochemical and/or textural information and independent constraints on the thermal and thus geologic history. Recent advances in our understanding of (U-Th)/He systematics, mass-spectrometry, and development of new (U-Th)/He and ⁴He/³He tools provide the foundation for interpreting increasingly complex datasets from diverse geologic settings. For example, radiation damage accumulation impacts He diffusivity in the apatite, zircon, and titanite and exerts a fundamental control on closure temperature and (U-Th)/He data patterns. This can be exploited to extract more information about thermal histories.

Here we offer current, new, and future method users from the spectrum of Earth science disciplines a forum to ask questions and discuss these systems, their complexities, and how to best apply these tools to effectively address their science questions. Information on sampling protocols and processing, aliquot selection, and available laboratories will be provided.