FROM DIAMOND-BEARING METAMORPHIC ROCKS OF THE KOKCHETAV MASSIF

. 40Ar/39Ar analyses were made on maruyamaite (potassium-dominant tourmaline) from tourmalinequartz-feldspar rocks discovered within the Kumdy-Kol microdiamond deposit (Kokchetav massif, North Kazakhstan). Turmaline yielded well-defined 40Ar/39Ar plateau age spectra whose values coincide within the error - ages of 502.3 & PLUSMN;8.0, 502.2 & PLUSMN;8.0, 506.0 & PLUSMN;8.0 Ma. These ages are much younger than the age of 530 & PLUSMN;2 Ma determined for high-pressure metamorphism by different methods. Thus, the formation of tourmaline-rich rocks of the Kumdy-Kol deposit cannot be associated with the high-pressure metamorphic events, and, therefore, testifies in favor of the low-pressure nature of maruyamaite. Based on the coincidence of age data for tourmaline crystals with different potassium contents, it can be concluded that the K/Ar system in tourmaline can be used for dating metasomatic and metamorphic processes.