Immiscible Transition from Carbonate-rich to Silicate-rich Melts in the 3 GPa Melting Interval of Eclogite + CO2 and Genesis of Silica-undersaturated Ocean Island Lavas

Abstract

We explore the partial melting behavior of a carbonated silicadeficient eclogite (SLEC1; 5 wt % CO2) from experiments at 3 GPa and compare the compositions of partial melts with those of alkalic and highly alkalic oceanic island basalts (OIBs). The solidus is located at 1050–1075 C and the liquidus at 1415 C. The sub-solidus assemblage consists of clinopyroxene, garnet, ilmenite, and calcio-dolomitic solid solution and the near solidus melt is carbonatitic ( 20 wt %), may be plausible sources or contributing components to melilitites and melilititic nephelinites from oceanic provinces, as they have strong compositional similarities including their SiO2, FeO*, MgO, CaO, TiO2 and Na2O contents, and CaO/Al2O3 ratios. Carbonated silicate partial melts from eclogite may also contribute to less extreme alkalic OIB, as these lavas have a number of compositional attributes, such as high TiO2 and FeO* and low Al2O3, that have not been observed from partial melting of peridotite CO2. In upwelling mantle, formation of carbonatite and silicate melts from eclogite and peridotite source lithologies occurs over a wide range of depths, producing significant opportunities for metasomatic transfer and implantation of melts.