Rodingite formation from diorite in the Samothraki ophiolite,NE Aegean,Greece

A metasomatic episode in the Samothraki ophiolite involved the formation of rodingites hosted in a diorite, which evolved by the interaction of an H₂O‐rich fluid phase. A pair of samples, which are in close spatial association, was used as an example to investigate this event. It is suggested that this process is characterized by the addition of Ca and the removal of Si and some large ion lithophile elements, under relatively oxidizing conditions where rare earth elements were fairly immobile. The Samothraki rodingites show common geochemical characteristics with similar lithologies elsewhere. A suggested T–X_CO2 path involves a prograde reaction series, which occurred below 550°C and slightly enriched the fluid phase in CO₂. A late infiltration of a highly hydrous fluid drove the fluid phase composition towards low CO₂ potential and led to the formation of late‐stage diopside and vesuvianite. Alternatively, if the fluid had been continuously controlled by an external source, only heating at temperatures below 500°C could have developed the whole process. Copyright © 2001 John Wiley & Sons, Ltd.