The closure temperature(s) of zircon Raman dating

Abstract

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 Tc for damage accumulation for each Raman band. Tc 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 (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.

Prolonged Slip on the South Tibetan Detachment Constrains Tectonic Models for Synorogenic Extension in the Central Himalaya

“…(2017), we used the standard equation for the estimation of alpha radiation dose (in units of α/g) as a function of time and parent element concentrations (e.g., Nasdala et al., 2001) to estimate the total amount of damage that might have occurred between MsAr closure in the discovery outcrop at 12.5 Ma and the ZrnHe or ApHe of each analyzed accessory mineral. Published studies suggest that alpha radiation damage does not accumulate significantly in the apatite or zircon structures during cooling until the temperatures drop below mineral‐specific threshold temperature ranges (Anderson et al., 2017; Flowers et al., 2009; Gautheron et al., 2009; Guenthner et al., 2013; Härtel et al., 2021), and those ranges for both minerals are substantially below the nominal closure temperature range for MsAr (Harrison et al., 2009). As a consequence, our calculated alpha doses (Figures 7b and 7d) should be regarded as high overestimates of doses at the time of (U‐Th)/He closure.…”

Zircon Raman thermochronology: Data valuation and measurement protocol

“…As for other thermochronological methods, the interpretation of zircon Raman ages depends on the thermal history of the dated sample. One aspect is the distinction of partial and complete annealing, marking the difference between mixed and reset ages (Wagner, 1981). For unannealed zircons, the measured radiation damage is equivalent to the zircon's -dose (D = D α α ), but decreases with annealing.…”

“…The radiation damage broadens the Raman bands and shifts them to lower wavenumbers. The Raman bandwidths provide a sensitive measure for the accumulated lattice damage (Nasdala et al, 1995;Nasdala et al, 2001). The measured bandwidth and the effective uranium concentration define the Raman age (Härtel et al, 2021).…”

“…In the case of partial annealing, however, the Raman age is a mixed age with no obvious geological significance. Mixed ages are difficult to interpret and cannot be distinguished from reset ages using the standard procedure for annealing detection (Nasdala et al, 2001). On the other hand, inhomogeneous damage distributions due to actinide zoning within zircon grains present a problem for zircon Raman dating.…”