Rodingitization and carbonation, associated with serpentinization of Triassic ultramafic cumulates and lavas in Othris, Greece

Abstract

The Othris region in Central Greece includes sub-oceanic crustal rocks of Middle-Late Triassic age that have undergone low to moderate degrees of metasomatic/metamorphic alteration processes. Alteration documented in these rocks includes rodingitization, serpentinization and carbonation in cumulate wehrlites, ultramafic lavas, mafic dykes and pillow-lavas. Wehrlites and ultramafic lavas are partially to completely serpentinized during ocean floor metamorphism. They were additionally affected by rodingitization, mostly expressed with formation of hydroandradites and hydrogrossulars, closely associated with the breakdown of primary phases of clinopyroxene and plagioclase. We estimate that rodingitization occurred within relatively mildly oxidizing physicochemical conditions, with an increased CO2/H2O ratio.More significant rodingitization affected mafic doleritic dykes that intrude wehrlites: this alteration occurred in parallel to serpentinization of hosting ultramafics via subsequent circulation of relatively alkaline and hydrous fluids. We have calculated that this occurred under low to moderate P-T conditions (180–320 °C, P ≈ 2–5 kbar). Circulation of Ca-rich fluids at shallower crustal levels was responsible for local carbonation phenomena, mostly affecting ultramafic and mafic pillow lavas.