Trends of variability of garnet megacryst composition from diamond-bearing and diamond-free kimberlite pipes (Yakutia)

The compositions of garnet megacrysts have been studied in representative collections from diverse kimberlite pipes of the Yakutian province. The megacrysts of garnet from diamond-bearing pipes show close ranes of composition and trends of variability. The megacrysts from diamond-free pipes differ in having relatively hih contents of FeO and low contents TiO2 and Cr2O3. In Mg-Fe-Ca diagram the compositions of megacrysts from diamond-bearing kimberlite form a trend parallel to the Mg-Fe axis with relatively constant Ca, while those from diamond-free kimberlite form a trend parallel to the Mg-Ca axis at relatively constant Fe. The compositions of mineral inclusions in megacryst garnets are reported and the paper considers megacryst genesis.