Estimation of radiation damage in titanites using Raman spectroscopy

Beatrix Muriel Heller (1, 2) , Nils Keno Lünsdorf (1) , István Dunkl (1) , Ferenc Molnar (3) , Hilmar von Eynatten (1)

1 Georg-August-University = Georg-August-Universität Göttingen
2 GEOPS - Géosciences Paris Sud
3 Geol Survey Finland, POB 96, FI-02151 Espoo, Finland

Recent studies have shown that a-damage in titanite influences He diffusivity and thus the closure temperature of the (U-Th)/He system in titanite. We compare different methods for measuring the alpha-dose in titanite by Raman spectroscopy. Raman spectra of randomly oriented titanite fragments from the Archean Karelian domain in eastern Finland along with some well-studied young titanites and U-Pb standard reference materials were analyzed and related to the concentration of alpha-emitting elements (U and Th) that generated damage in the respective grains. Automated curve-fitting was performed by the IFORS software and different curve-fitting protocols were tested and compared. The Raman bands at 424 and 465 cm(-1) show a good correlation of full-width at half maximum (FWHM) and position with the alpha-dose. However, these bands are not always present because titanite is highly anisotropic implying that Raman spectra are sensitive to orientation. The intensity-weighted mean FWHM (iw-FWHM) of all Raman bands of a spectrum proves to be the most robust measure of the alpha-dose. A simplified fitting approach considering 15 peaks is sufficient to describe the accumulated alpha-dose. For alpha-doses below 5 x 10(16)alpha/g the iw-FWHM is independent of alpha-dose and ranges from 25 to 50 cm-1. Above this value the iw-FWHM increases linearly with increasing alpha-dose up to 3 x 10(18)alpha/g. The linear correlation can be described as iw-FWHM[cm(-1)] approximate to 39(+/- 1.2)[cm(-1)] + 3.84(+0.61,-0.26) x 10(-17)[cm(-1)/(alpha/g)] x alpha-dose[alpha/g]. The approach provides a pre-selection method to optimize the range of alpha-doses of titanite crystals to be dated by (U-Th)/He thermochronology.

Domaines: Planète et Univers [physics]; Sciences de la Terre

Beatrix Muriel Heller, Nils Keno Lünsdorf, István Dunkl, Ferenc Molnar, Hilmar von Eynatten. Estimation of radiation damage in titanites using Raman spectroscopy. The American Mineralogist, 2019, 104 (6), pp.857-868. ⟨10.2138/am-2019-6681⟩. ⟨hal-02158764⟩