Program > Browse abstracts by speaker > Dalou Celia

High-pressure experimental samples are used to quantify C and S elemental and isotopic fractionations during core formation. Although bulk measurements can be performed to accurately determine isotopic fractionations, sample textures may require the use of local micro-analytical techniques, such as secondary ion mass spectrometry (SIMS).

However, SIMS analyses involve calibration and the determination of instrumental mass fractionation (IMF) in reference materials with matrix compositions similar to those of unknown samples. To provide metallic reference materials adapted to C and S measurements via SIMS, we synthesized a series of alloys comprising four FeNi(±Si) compositions (Fe95Ni5, Fe90Ni10, Fe80Ni20, Fe80Ni15Si5), with C or S contents varying from 100 ppm to 4 wt%. We used the "melt spinning" method (IJL, Nancy) to rapidly quench the alloys at ~10^6 K/s. Elemental contents were determined by CS analyser (SARM, CRPG), absolute d13C values by IRMS (Thermoscientific Delta V), and absolute d34S values by MC-ICP-MS (ThermoScientific Neptune).

Preliminary results suggest C isotopic fractionation during melting, with d13C values varying between −28.71 ± 0.34‰ and −13.29 ± 0.07‰ in samples containing 1000 ppm to 2 wt% C. In contrast, S did not undergo isotopic fractionation during sample synthesis; we consistently obtained d34S = 16.01 ± 0.31‰, indistinguishable from the d34S value of the FeS starting material.

We observed no effect of matrix Fe-Ni, Si, or S content on S calibration curves and IMF for d34S measurements. In contrast, we observed that calibration curves for C contents significantly change with the Fe/Ni ratio, and more so with the addition of Si. Additional absolute d13C measurements will reveal if similar effects impact IMF for d13C measurements.

We ultimately recommend eight S-bearing samples as reliable reference materials for S isotopic measurements by SIMS, available to other laboratories worldwide, and we are currently completing our study on C-bearing samples.