Formation of Polycrystalline Graphite Aggregates in High-Pressure Metamorphic Rocks from the Kokchetav Massif, Northern Kazkhstan

An inclusion of graphite in zircon from the diamond- and tourmaline-bearing rocks of the Kokchetav massif (Northern Kazakhstan) has been studied. The inclusion, associated with diamond crystals, was identified within the marginal part of the zircon grain. The Raman spectrum of the graphite inclusion is characterized by the presence of an intense band at 1350 cm–1, which is indicative of a high degree of disorder in its structure. An investigation of this inclusion by means of transmission electron microscopy (TEM) allowed us to identify nine randomly oriented high-ordered submicron grains of graphite without relics of diamond. Thus, the presence of the intense band at 1350 cm–1 in the Raman spectra of graphite is not a necessary evidence of its low degree of crystallinity and particularly its formation as a result of diamond graphitization. The formation of the polycrystalline aggregates, consisting of submicron grains of well-ordered graphite, might have been related to rapid crystallization from a high-density C–O–H fluid.