Multi‐Band Raman Analysis of Radiation Damage in Zircon for Thermochronology: Partial Annealing and Mixed Signals

Abstract

Thermochronology studies the timing and rates of geologic phenomena based on the radioactive processes occurring within natural minerals. At the same time, these processes damage the mineral, changing its properties over time. Measurements of self-irradiation damage are thus an important part of thermochronologic studies. Such measurements broke ground for: (a) zircon Raman dating, in which the self-irradiation damage itself is a measure of the age of the sample (Härtel, Jonckheere, Wauschkuhn, Hofmann, et al., 2021;Pidgeon, 2014); (b) the refinement of thermochronometers, whose results are influenced by self-irradiation damage, for example, (U-Th)/ He dating (Anderson et al., 2020;Guenthner et al., 2013); and (c) the applicability of provenance studies, using Raman characteristics of detrital zircons to distinguish thermal histories (Garver & Davidson, 2015;Resentini et al., 2020).Zircon (ZrSiO 4 ) substitutes U and Th for Zr in its structure. Disintegration of 238 U, 235 U, 232 Th, and their daughters damages the lattice by the emission of α-particles and the recoil of the daughter nuclei (Bohr, 1948;Joly, 1907;Mügge, 1922). An α-particle displaces ∼10 2 atoms toward the end of its ∼10-20 μm trajectory through the

Duluth Complex FC1 Apatite and Zircon: Reference Materials for (U‐Th)/He Dating?

“…Fourth, the linear He‐eU relationship shows that He retention in the FC1 zircon was unaffected by radiation damage, although Härtel et al . (2022b) reported the occurrence of high‐damage grains above the α‐dose‐threshold of Guenthner et al . (2013) for enhanced He loss.…”

“…Likewise, Raman spectrometry indicates homogeneous intra‐grain radiation damage in FC1 zircon (Härtel et al . 2022b). Third, the size of the grains and the rapid cooling through the zircon He PRZ (~ 160–200 °C) make a heterogeneous He distribution within grains due to volume diffusion unlikely.…”

A zircon classification scheme for sedimentary provenance analysis using radiation damage

“…The high FWHM is because of significant band asymmetry, likely resulting from substitution‐related strain and disorder (Kempe et al, 2018). The band asymmetry is alternatively explained by damage heterogeneity within a single analysis spot because of a contrasting distribution of actinide elements in zircons (Härtel et al, 2022; Nasdala et al, 2005). The very low α‐dose of hydrothermal zircons is related to the low concentrations of Th and U compared with most magmatic zircons, because such zircons experience migration of U and Th because of fluid activity (Schaltegger, 2007; Tichomirowa et al, 2005).…”

“…For zircons with complex structures (e.g., core–mantle‐rim), the U–Pb ages, U and Th concentrations, and Raman measurements are from the same spot. Zircons with discordant U–Pb ages (e.g., zircons outside the range of 90%–110% concordance in the 238 U/ 206 Pb and 206 Pb/ 207 Pb ages) and heterogeneous grains that show large variations of FWHM and Raman shift within a single zircon were removed (e.g., Härtel et al, 2022). The collected bandwidths were recalculated for the instrumental profile function (IPF) following Váczi (2014).…”

Structural characteristics of radiation‐amorphized ZrSiO4:U,Th according to Raman spectroscopy of Boson peak

“…The tensilecompression stresses, discovered earlier in the crystalline zircon fraction, are still not explored in the amorphous fraction. The spectroscopic estimates of radiation damage to zircon proposed in the literature are based solely on the analysis of the spectra of its crystalline fraction, [13,37,38] while there are no detailed studies of the structure, properties and evolution of the amorphous fraction.…”