Methane in Carbonate Melt Inclusions in the Rock-Forming Minerals of Calc-Silicate Rocks of the Kokchetav Massif

Abstract

Secondary inclusions of the carbonate melt in garnets and clinopyroxenes from ultrahigh-pressure calc-silicate rocks were studied. Secondary carbonate inclusions are located in the healed cracks confined to large (100 µm–3 mm) primary carbonate inclusions in garnet. In some cases, the healed cracks form plates that intersect both garnet and inclusions of potassium-bearing clinopyroxene in garnet. The high content of K2O (0.64 wt %) in the healed cracks in clinopyroxene inclusions suggests that their formation and healing took place during the stage of ultrahigh pressures. Interpretation of the Raman spectra of the secondary inclusions of the carbonate melt in garnet and clinopyroxene confirmed the presence of the following phases: methane, graphite, calcite, dolomite, muscovite, and phlogopite. The data obtained allowed us to recognize the stage of ultrahigh pressure metamorphism in the calc–silicate rocks of the Kokchetav massif, during which methane accumulation in the carbonate melt took place, for the first time.