Abstract
Abstract. Zircon Raman dating based on irradiation damage
is a debated concept but not an established geo-/thermochronological
method. One issue is the temperature range of radiation-damage annealing
over geological timescales. We conducted isochronal and isothermal annealing
experiments on radiation-damaged zircons between 500 and 1000 ∘C
for durations between 10 min and 5 d to describe the annealing
kinetics. We measured the widths (Γ) and positions (ω) of
the ν1(SiO4), ν2(SiO4), and ν3(SiO4) internal Raman bands, and the external rotation Raman
band at ∼974, 438, 1008, and 356 cm−1 after each
annealing step. We fitted a Johnson–Mehl–Avrami–Kolmogorov and a distributed
activation energy model to the fractional annealing data, calculated from
the widths of the ν2(SiO4), ν3(SiO4), and
external rotation bands. From the kinetic models, we determined closure
temperatures Tc for damage accumulation for each Raman band. Tc
ranges from 330 to 370 ∘C for the internal ν2(SiO4)
and ν3(SiO4) bands; the external rotation band is more
sensitive to thermal annealing (Tc∼260 to
310 ∘C). Our estimates are in general agreement with previous
ones, but more geological evidence is needed to validate the results. The
Tc difference for the different Raman bands offers the prospect of a
multi-closure-temperature zircon Raman thermochronometer.
Funder
Deutsche Forschungsgemeinschaft
Studienstiftung des Deutschen Volkes
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