Confocal Raman Imaging of Secondary Carbonate‐Bearing Inclusions From the UHP Calc‐Silicate Rocks (Kokchetav Massif): Hydrous Carbonatitic Melt/Fluid Origin and Carbonate‐Bearing Inclusions Evolution

ABSTRACT Findings of primary carbonate‐bearing inclusions in garnet porphyroblasts from the calc‐silicate rock of the Kokchetav massif indicate the presence of hydrous carbonatitic melt at the UHP peak metamorphism. However, two contrasting hypotheses exist for the formation of these inclusions: (1) Inclusions were trapped by garnet in the form of primary carbonatitic melt at peak metamorphism, and (2) inclusions were trapped as mineral aggregate during the prograde metamorphic stage and underwent melting close to the UHP peak metamorphism. A thorough Raman study revealed that UHP secondary carbonate‐bearing inclusions, located in healed cracks, contain calcite, dolomite, quartz, phengite/muscovite, graphite, and CH4, whereas primary carbonate‐bearing inclusions exhibit a distinct mineral association comprising phlogopite, calcite, dolomite, graphite/diamond, allanite, and chlorite. Most likely, primary inclusions initially were trapped as hydrous carbonatitic melt/fluid + mineral aggregate ± silicate melt in the garnet/clinopyroxene. Melting of this mineral aggregate in primary inclusions or decompression at the UHP conditions ( P > 3.5 GPa) resulted in brittle failure of the host mineral and formation of secondary inclusions chains. Both types of inclusions contain daughter minerals and step‐daughter silicates formed by the reaction of the carbonatitic melt/fluid and host garnet. In contrast to the primary inclusions, the secondary inclusions almost do not contain accidentally trapped and retrograde minerals and, thus, are the most suitable for the UHP carbonatitic melt/fluid reconstruction.