TY - JOUR
T1 - Annealing kinetics of radiation damage in zircon
AU - Ginster, Ursula
AU - Reiners, Peter W.
AU - Nasdala, Lutz
AU - Chanmuang N., Chutimun
N1 - Funding Information:
We thank Cécile Gautheron, Kalin McDannell, and an anonymous reviewer for constructive comments that helped improve this paper. We thank Dr. Thorsten Geisler for sending us the HZ5 data. We thank Dr. Paul Wallace for support with the Renishaw InVia Raman microscope at the University of Arizona. The Horiba LabRAM HR Evolution was located at the University of Vienna, Austria. We thank Dr. George E. Gehrels at the University of Arizona for providing shards of SLB and SLC as well as their U-Pb ages. We thank Dr. Dmitry A. Zamyatin (Zavaritsky Institute of Geology and Geochemistry, Ural Branch, Russian Academy of Sciences, Yekaterinburg, Russia) for performing preliminary EPMA analyses on the GZ samples. And we thank Sarah E.M. Gain [CCFS (Australian Research Council Centre of Excellence for Core to Crust Fluid Systems) and GEMOC (Australian Research Council National Key Centre for Geochemical Evolution and Metallogeny of Continents), Department of Earth and Planetary Sciences, Faculty of Science and Engineering, Macquarie University, Sydney, Australia] for determining U-Pb ages for the GZ samples.
Funding Information:
This research was supported by the National Science Foundation (NSF) Graduate Research Fellowship Program award to Ursula Ginster and by the NSF Grant EAR-1426749 to Peter Reiners.
Publisher Copyright:
© 2019 Elsevier Ltd
PY - 2019/3/15
Y1 - 2019/3/15
N2 - Models of noble-gas diffusion in minerals are essential for thermochronologic interpretations used for understanding the timing and rates of a range of geologic processes including exhumation and burial. For some minerals, diffusive daughter loss depends not only on temperature but also radiation damage. This is particularly true for the zircon (U-Th)/He system. Consequently, realistic interpretation of zircon (U-Th)/He thermochronology needs to account for both accumulation as well as annealing of radiation damage as a function of time and temperature. To date, models use etchable fission track annealing as a proxy for bulk radiation damage annealing. Here we present experimental annealing data and models of bulk radiation damage annealing kinetics in zircon. We show that bulk radiation damage annealing requires significantly higher temperatures and longer durations than that of etchable fission tracks. When fission tracks are completely annealed, bulk radiation damage has been annealed by only 30–50%. Consequently, a zircon (U-Th)/He thermochronology model that uses a fission track annealing algorithm will overestimate annealing resulting in erroneous estimates of He diffusivities and He loss. A time-temperature (t-T) history derived using the fission track annealing algorithm can, therefore, differ significantly from a t-T path derived using bulk radiation damage annealing kinetics. We also show that fractional-annealing-progress depends on the extent of accumulated radiation damage. Accordingly, we present distinct annealing models for low-, moderate-, and high-damage zircon. Each model comprises three annealing regimes with distinct kinetic parameters. The low-fractional annealing (low-φ) regime applies at low temperatures and short heating durations, whereas the high-φ regime applies at high temperatures and long durations. Between the two is a transition regime. We attribute the change in annealing kinetics to the presence of multiple damage-induced defect types that anneal with different activation energies and, therefore, at distinct time-temperature conditions. Comparison with other studies suggest that the low-φ regime is dominated by annealing of point defects that anneal at low temperatures, whereas the high-φ regime is dominated by epitaxial growth and annealing of isolated, stable point defects that anneal with high activation energies.
AB - Models of noble-gas diffusion in minerals are essential for thermochronologic interpretations used for understanding the timing and rates of a range of geologic processes including exhumation and burial. For some minerals, diffusive daughter loss depends not only on temperature but also radiation damage. This is particularly true for the zircon (U-Th)/He system. Consequently, realistic interpretation of zircon (U-Th)/He thermochronology needs to account for both accumulation as well as annealing of radiation damage as a function of time and temperature. To date, models use etchable fission track annealing as a proxy for bulk radiation damage annealing. Here we present experimental annealing data and models of bulk radiation damage annealing kinetics in zircon. We show that bulk radiation damage annealing requires significantly higher temperatures and longer durations than that of etchable fission tracks. When fission tracks are completely annealed, bulk radiation damage has been annealed by only 30–50%. Consequently, a zircon (U-Th)/He thermochronology model that uses a fission track annealing algorithm will overestimate annealing resulting in erroneous estimates of He diffusivities and He loss. A time-temperature (t-T) history derived using the fission track annealing algorithm can, therefore, differ significantly from a t-T path derived using bulk radiation damage annealing kinetics. We also show that fractional-annealing-progress depends on the extent of accumulated radiation damage. Accordingly, we present distinct annealing models for low-, moderate-, and high-damage zircon. Each model comprises three annealing regimes with distinct kinetic parameters. The low-fractional annealing (low-φ) regime applies at low temperatures and short heating durations, whereas the high-φ regime applies at high temperatures and long durations. Between the two is a transition regime. We attribute the change in annealing kinetics to the presence of multiple damage-induced defect types that anneal with different activation energies and, therefore, at distinct time-temperature conditions. Comparison with other studies suggest that the low-φ regime is dominated by annealing of point defects that anneal at low temperatures, whereas the high-φ regime is dominated by epitaxial growth and annealing of isolated, stable point defects that anneal with high activation energies.
KW - Annealing
KW - Annealing model
KW - Fanning linear Arrhenius model
KW - Radiation damage
KW - Zircon
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U2 - 10.1016/j.gca.2019.01.033
DO - 10.1016/j.gca.2019.01.033
M3 - Article
AN - SCOPUS:85061202074
SN - 0016-7037
VL - 249
SP - 225
EP - 246
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
ER -