EXPANDING APPLICATIONS OF ZIRCON (U-TH)/HE THERMOCHRONOMETRY BY EVALUATING VISUAL METAMICTIZATION AS A RELIABLE PROXY FOR ACCUMULATED RADIATION DAMAGE
Here we evaluate the visual metamictization approach and estimations of radiation damage dose in zircon grains from Archean and Proterozoic samples investigated in Ault et al. (2018), as well as a sample of the Miocene Punchbowl formation with likely Phanerozoic zircon grains. We compare the visual metamictization from dated grains, corresponding ZHe dates, and calculated alpha dose from U and Th decay equations assuming damage accumulates since the U-Pb crystallization age, and from thermal history modeling using the Guenthner (2021) DAAM code and Guenthner et al. (2013) and Ginster et al. (2019) annealing kinetics. These relationships reveal, as expected, that damage calculated from decay equations exceeds that from thermal history modeling for each grain and sample. Grain metamictization tracks damage regardless of calculation approach, even for the samples characterized by uniform ZHe dates regardless of eU. This suggests that visual metamictization provides a first order estimate of accumulated damage. Ongoing work involves comparing these damage estimates with damage inferred from Raman spectroscopy of new grains that have commensurate visual damage to evaluate the robustness of the metamictization approach and understand damage annealing.