Raman mapping reveals alpha radiation damage zonation and its annealing in Durango apatite

The accumulation of alpha radiation damage and its annealing in apatite are critical to thermochronological studies but remain difficult to characterize. We conducted annealing experiments on four slices from a single Durango apatite crystal and used high-resolution Raman spectroscopy mapping to analyse peak positions and full width at half maximum (FWHM) of the ν₁(PO₄) and ν₃(PO₄) bands. Track densities were measured in different regions of the crystal, and a normalized track-density reduction model was applied to estimate the original alpha radiation damage. In addition, heavy-ion irradiation was used to simulate the fission process and enhance the visibility of confined tracks.

Our results show that the FWHM of the ν₁(PO₄) band is a robust indicator of alpha radiation damage accumulation in apatite and does not correlate with fission-track damage in Durango apatite. The spatial zoning pattern of FWHM closely matches that of effective uranium (eU), and among samples with similar eU contents, those subjected to higher annealing temperatures exhibit lower FWHM values. Furthermore, alpha radiation damage does not significantly influence the annealing behaviour of fission tracks in Durango apatite. Although the behaviour of Raman peak positions remains enigmatic, our results suggest that it is influenced by both apatite chemical composition and radiation damage accumulation. This study demonstrates that high-resolution Raman spectroscopy provides a novel and quantitative approach to directly link radiation damage with thermal history in apatite. This methodology could potentially improve thermochronological apatite models and interpretation enabling detailed, spatially resolved insights into damage accumulation and annealing processes in geological studies.