Evolution of rodingites along stratigraphic depth in the Iti and Kallidromon ophiolites (Central Greece)

Abstract Rodingitised rocks were collected from the neighbouring Iti and Kallidromon ophiolites. They comprise metasomatic assemblages after serpentinised lherzolite and harzburgite, gabbro and dolerite dykes. The main mineral phases in the metasomatised mantle and gabbroic rocks include grossularitic garnet, chlorite and diopside whereas epidote group minerals were mainly developed at the expense of the dolerite dykes. The fluid phase involved in the metasomatic reactions was highly alkaline in the metasomatising peridotites and less alkaline in the altered gabbro and dolerite. Under such conditions, Ti is assumed to have remained immobile in the whole process while Zr remained constant in the stratigraphically upper rodingitised gabbro and dolerite. Transportation of rare earth elements, Zr, Cr and Ni from the altered mantle segment to the upper gabbro level was assisted by the presence of carbonate and hydroxyl ligands. After consequent breakdown of the carbonate complexes, these elements were deposited in the rodingitised gabbro and dolerite. Rare earths were mainly integrated in the neoblastic diopside whereas Cr and Ni likely formed insoluble hydroxides in that less reducing environment. The metasomatic event happened in the mantle wedge close to the subduction of the Pelagonian carbonates that strongly enriched the fluid phase in CO2. The entrance of an externally derived hydrothermal fluid was responsible for the reduction of pH at the higher levels and the calculated influx of Si in the system.