Implementation of an Alpha Damage Annealing Model for Zircon (U-Th)/He Thermochronology With Comparison to a Zircon Fission Track Annealing Model

Radiation damage exerts a fundamental control on He diffusion in zircon, which manifests as correlations between (U-Th)/He date and effective uranium concentration. These correlations can be exploited with modeling to explore long-term thermal histories. This manuscript focuses on one such model, the zircon radiation damage accumulation and annealing model (ZRDAAM) of Guenthner et al. (2013), https://doi.org/10.2475/03.2013.01, by integrating newly defined alpha damage annealing kinetics measured by Ginster et al. (2019), https://doi.org/10.1016/j.gca.2019.01.033, into ZRDAAM. I explore several consequences of this alpha damage annealing model as it relates to (U-Th)/He date-effective uranium (eU) correlations, using representative time-temperature paths and previously published results. Comparison between the current version of ZRDAAM, which uses fission track annealing, and the new annealing model demonstrates that, for thermal histories with prolonged periods at low temperatures (<50 degrees C), alpha dose annealing kinetics yield slightly younger model dates at low to moderate eU concentrations, older dates at moderate to high eU, and substantially younger dates at the highest eU concentrations. The absolute eU concentrations over which the differences are observed varies for a given thermal history, so these ranges should be interpreted as relative or proportional. Younger model dates at high eU in most thermal histories result from lower amounts of annealing that occur with the Ginster et al. (2019) alpha dose annealing kinetics. This annealing model comparison illustrates that the choice of annealing kinetics has the greatest influence over model output for thermal histories involving either prolonged time periods in the 200-300 degrees C temperature window, or a late-stage reheating event.

Automated summary

Radiation damage plays a crucial role in controlling He diffusion in zircon, leading to correlations between (U-Th)/He dates and effective uranium concentration. The integration of alpha damage annealing kinetics into the ZRDAAM model shows that lower temperatures result in slightly younger model dates, while higher uranium concentrations lead to older dates. These differences are most pronounced in thermal histories with extended periods at low temperatures.