Program > Browse abstracts by speaker > Bolfan Nathalie

The most abundant mineral in the upper mantle, olivine, is described as nominally anhydrous while its high-pressure polymorph, wadsleyite, can contain up to 3% H2O by weight. Here we focus on the quantification of total H2O content, dissolved as hydroxyl (OH), as well as hydrogen isotopic composition, i.e. ratios, in olivine and wadsleyite using a multi-instrument approach. Our aim is to establish a calibration procedure that allows accurate quantification of the hydrogen content and ratios of D-doped experimental samples using Raman spectroscopy, as confirmed by secondary-ion mass spectrometry (SIMS). Olivine and wadsleyite samples were synthesized under hydrothermal conditions at high pressure and doped with deuterium. Olivine and wadsleyite reference materials that were previously characterized by both FTIR (Fourier Transform Infrared) spectroscopy and ERDA (Elastic Recoil Detection Analysis) were used to calibrate the measurement of water concentrations in the samples using both Raman and SIMS. D-doped olivine reference materials were characterized by ERDA (which is a point beam technique with the advantage to be an absolute quantification method) for their D/H ratio and used to determine the instrument mass fractionation of H isotopes by the ion probe. Then we compared the D/H ratios determined by SIMS to the OD/OH intensity ratio determined by Raman spectroscopy for three wadsleyite samples, finding a conversion factor of 0.85 (error < 1%). After correction of the instrument response, we find that the Raman scattering cross-section (K) of OH is slightly lower than that of OD, still KOH/KOD = 0.95 in agreement with previous studies. Ratios in doped samples can therefore be determined using Raman spectroscopy, which is a more accessible technique than SIMS, with a detection limit of 90 ± 10 ppm wt. for both D2O and H2O.