The transition from carbonatitic to carbonate-silicate magmas in carbonated eclogites

In the last decades, several studies focused on the effect of CO2 on phase equilibria within carbonated eclogitic rocks to achieve information about the deep carbon cycle and the processes that control the carbon storage into the Earth’s mantle. Nowadays the effect of temperature (T), pressure (P) and oxygen fugacity (fO2) on the melt composition remains still unclear. This experimental study aims to determine the melt composition of CO2-rich melts at fO2 buffered by the coexistence of carbon and carbonate as function of P and T. We performed experiments using Voggenreiter 840 t Walker-type multi anvil press available at HP/HT Lab at National Institute of Geophysics and Volcanology (INGV) in Rome. We employed for all the experiments a synthetic starting material representative of the Dolomite-Coesite-Diopside-Graphite buffering assemblage (DCDG; Luth, 1993), doped with FeTiO3 and TiO2 and ~3 wt% iridium used as redox sensor to calculate the oxygen fugacity during each experiment. The obtained results have been combined with published data (Stagno et al., 2015), and compared with thermodynamic calculations (Luth, 1993). Preliminary results demonstrated that the transition from a carbonatitic melt (1-5 wt% SiO2) formed at 900°C and a hybrid carbonate-silicate melts (20-25 wt% SiO2) formed at 1200°C can occur within less than 1 log unit of fO2 by a process called redox melting of elemental carbon-bearing eclogite rocks.