Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The arrival of new LA-ICP-MS equipment at UQAC allowed us to analyse the Os, Ir, Ru and Rh contents of chromite from samples representative of different geological settings including MORB, boninites, komatiites, continental flood basalt picrite, continentaltype and oceanic-type chromitites, and chills of the Bushveld Complex. Our new LA-ICP-MS results combined with previous data confirm that chromite could act as the dominant phase in controlling the whole rock budget of Os, Ir, Ru and Rh, but chromite generally share this role with other phases like PGM whose crystallization seems to be influenced by chromite crystallization. Most primitive mantle normalized PGE profiles of chromite show RuN>RhN with the exception of boninite and arc lavas which tend to show RuN<RhN. The chromite from each different setting has distinctive PGE normalized profiles that can be used to identify parental magma. For example the chromite from the chills of the Bushveld lies between komatiites and picrite rather than boninite.