21-EPN-FT1-006: Melting phase relations of subduction zone minerals and their nitrogen budget
June 3, 2023

21-EPN-FT1-006: Melting phase relations of subduction zone minerals and their nitrogen budget

Visit by Caterina Melai, University of Bayreuth (Germany) to TA2.9 Ion Probe Facility (IPF), CRPG (France).
Dates of visit: 29 August – 02 September 2022

Report Summary: In this study the phase relations of hydrous aluminosilicate minerals (e.g. montmorillonite, phlogopite, phengite and serpentinite) that are present in sedimentary layers or form during early prograde metamorphism of the oceanic lithosphere are investigated at sub-arc conditions. The investigated minerals are potential hosts for nitrogen at different P-T conditions along the subducting slab, depending on their phase stabilities and the N partitioning upon partial melting of these phases. In the present analytical session, several minerals in equilibrium with melt (quenched glass) have been analysed by means of SIMS.

The measurements in this report were performed using the CAMECA 1280 HR2 Ion Probe at CRPG, France. All the experimental capsules planned for the session were analysed and additional secondary standards were investigated.

The experimental samples showed consistent and reproducible N content on the different measured spots both on the mineral and the melt phase. More challenging was the measurements of the standards that confirmed the existing concern on the possible matrix effect during SIMS measurements of mineral phases. The different behaviour of the light elements analysed in a glass or crystalline matrix appears to have a strong effect on the measured nitrogen ion yield.

The work performed during this analytical session at the SIMS, allowed the acquisition of the N data for the calculation of the partition coefficients between mineral and melt while providing additional evidence for the need of further investigation of the matrix effect for this technique.

Read the full scientific report, with kind permision from Caterina Melai.