Séminaire - The paradox of moissanite:a new finding in syenitic rocks - Sabrina Nazzareni

IMPMC - Sorbonne Université - 4 place Jussieu, 75005 Paris, tour 23, 4^e étage, couloir 22-23, salle 401

Lundi 3 décembre 2018, 14 h 30

Sabrina Nazzareni - University of Perugia

Abstract

Since its discovery in 1893, moissanite (SiC) was recovered in an increasing number of terrestrial tectonic settings: as inclusions in diamonds, in kimberlites, ophiolites, granulites and metamorphic rocks, and in volcanic breccias. The presence of moissanite in such different rocks opened an intense debate to explain its origin, mainly because it only forms at extremely reducing conditions, i.e. fO2 5-7 log units below Iron-Wustite (IW) for mantle conditions (P = 2-10 GPa T = 1000-1700°C). Despite the increased findings from continental crust sources, moissanite has never been reported from present-day oceanic geodynamic settings.
We discovered moissanite grains in a concentrated diamagnetic fraction from a peralkaline syenite from Azores Islands (Portugal). Moissanite has been characterised by micro-Raman spectroscopy (μ-RS), single-crystal X-ray diffraction (SC-XRD) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Beside, inclusions hosted in moissanite were characterized by μ-RS .