The closure temperature(s) of zircon Raman dating

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.

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

“…In an approach similar to that of Anderson et al (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.…”

Investigating the Shallow to Mid-Depth (>100–300 °C) Continental Crust Evolution with (U-Th)/He Thermochronology: A Review

“…The radiation damage ages also have a remarkable spread that mirrors that of the ZHe dates, though they are consistently older. These observations suggest that the analyzed zircon crystals also experienced partial annealing under temperature conditions similar to those of the ZHe PRZ, though the consistently older ages (in comparison to the ZHe results) are in disagreement with most estimates that the temperatures necessary for significant zircon annealing are higher than for widespread He diffusion ( [92] and references therein). In addition, the calculated ages correlate with eU, showing evidence that crystals with varying damage densities were subjected to different annealing mechanisms or rates.…”

“…Depending on the target of a study, poorly or highly damaged crystals can be chosen using this tool. In the case of zircon, there is furthermore the possibility of calculating zircon damage dates [91][92][93], which can be an interesting complement to ZHe dating [94]. According to Härtel et al [92], the zircon damage T c ranges from 260 to 370 • C and is therefore slightly higher than the ZHe T c .…”

A zircon classification scheme for sedimentary provenance analysis using radiation damage

“…Schematic diagram showing the different emplacement routes of rocks and the temperature range of zircon crystallization and annealing. Route I: rocks cooling at high rates (e.g., volcanic rocks) rapidly pass through the temperature range of zircon crystallization and radiation‐damage annealing (Härtel, Jonckheere, Wauschkuhn, Hofmann, et al, 2021; Härtel, Jonckheere, Wauschkuhn, & Ratschbacher, 2021; Pidgeon, 2014). Route II: rocks being slowly exhumed reside a prolonged time in the temperature range between zircon crystallization and annealing, e.g., rocks of a granitic batholith.…”

“…In many high‐grade metamorphic rocks, zircons recrystallize and thus experience a reset of the U–Pb isotopic system. Such zircons undergo a complete repair of radiation damage and only accumulate new damage after cooling through the temperature range in which annealing occurs (see below; Härtel, Jonckheere, Wauschkuhn, & Ratschbacher, 2021). When these high‐grade metamorphic rocks are rapidly exhumed through this radiation‐damage annealing zone, the high cooling rate prevents significant annealing.…”