The closure temperature(s) of zircon Raman dating

Abstract. We conducted isochronal and isothermal annealing experiments on radiation-damaged zircons between 500 and 1000 °C for durations between ten minutes and five days. We measured the widths (Γ) and positions (ω) of the internal ν₁(SiO₄), ν₂(SiO₄), ν₃(SiO₄), and external rotation Raman bands at ~ 974, 438, 1008, and 356 cm⁻¹. 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 T_c for damage accumulation for each Raman band. T_c range from 330 to 370 °C for the internal ν₂(SiO₄) and ν₃(SiO₄) bands; the external rotation band is more sensitive to thermal annealing (T_c ~ 260 to 310 °C). Our estimates are in general agreement with previous ones, but more geological evidence is needed to validate the results. The T_c difference for the different Raman bands offers the prospect of a multi-closure-temperature zircon Raman thermochronometer.