Internal Sources of Co During Anatexis Under Conditions of High-Temperature Metamorphism (Experimental Data)

Partial melting experiments of garnet-two-mica schist containing 0-20 wt. % graphite were carried out at 900°C and 500 MPa. Experiments have shown that at all graphite contents (within the specified range), metapelite melts are formed by peritectic melting reactions of biotite, muscovite and partly quartz: Bt + Ms + Qz → Kfs + Spl(Hc) + oAm + Sil + Gl. The decreasing Fe/(Fe+Fe) ratio in Fe-Mg minerals with increasing graphite content reflects increasing reducing conditions. Oxygen released as a result of the oxidation-reduction reactions of iron reacts with graphite to form CO. It partially dissolves in the melt to form carbonate complexes of Ca, Mg, K and accompanies it in the form of a free fluid phase. Experiments demonstrate that graphite-bearing metapelites can serve as efficient internal sources of CO during high-temperature metamorphism.