| Summary: | <p>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 <span class="inline-formula"><sup>∘</sup></span>C
for durations between 10 min and 5 d to describe the annealing
kinetics. We measured the widths (<span class="inline-formula">Γ</span>) and positions (<span class="inline-formula"><i>ω</i></span>) of
the <span class="inline-formula"><i>ν</i><sub>1</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>), <span class="inline-formula"><i>ν</i><sub>2</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>), and <span class="inline-formula"><i>ν</i><sub>3</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>) internal Raman bands, and the external rotation Raman
band at <span class="inline-formula">∼974</span>, 438, 1008, and 356 cm<span class="inline-formula"><sup>−1</sup></span> 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 <span class="inline-formula"><i>ν</i><sub>2</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>), <span class="inline-formula"><i>ν</i><sub>3</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>), and
external rotation bands. From the kinetic models, we determined closure
temperatures <span class="inline-formula"><i>T</i><sub>c</sub></span> for damage accumulation for each Raman band. <span class="inline-formula"><i>T</i><sub>c</sub></span>
ranges from 330 to 370 <span class="inline-formula"><sup>∘</sup></span>C for the internal <span class="inline-formula"><i>ν</i><sub>2</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>)
and <span class="inline-formula"><i>ν</i><sub>3</sub></span>(SiO<span class="inline-formula"><sub>4</sub></span>) bands; the external rotation band is more
sensitive to thermal annealing (<span class="inline-formula"><i>T</i><sub>c</sub>∼260</span> to
310 <span class="inline-formula"><sup>∘</sup></span>C). Our estimates are in general agreement with previous
ones, but more geological evidence is needed to validate the results. The
<span class="inline-formula"><i>T</i><sub>c</sub></span> difference for the different Raman bands offers the prospect of a
multi-closure-temperature zircon Raman thermochronometer.</p>
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