Internal CO2 Sources during Anatexis under High-Temperature Metamorphism: Experimental Data

Experiments on partial melting of garnet–two mica schist with 0–20 wt % graphite were carried out at 900°C and 500 MPa. The experiments showed that, at all graphite contents, the melts form due to reactions of peritectic melting of biotite, muscovite, and partly quartz: Bt + Ms + Qz → Kfs + Spl(Hc) + Sil + Gl ± oAm. A decrease in the Fe3+/(Fe3+ + Fe2+) ratio of Fe–Mg minerals with an increasing amount of graphite reflects the enhanced reducing conditions. Oxygen, which is released as a result of oxidation–reduction of Fe, interacts with graphite, which leads to the formation of CO2. It is partly dissolved in the melt with the formation of Ca, Mg, and K carbonate complexes and accompanies the melt in the form of a free fluid phase. The experiments show that the graphite-bearing metapelites could be effective internal CO2 sources under high-temperature metamorphism.