Ultramafic Alkaline Rocks of Kepino Cluster, Arkhangelsk, Russia: Different Evolution of Kimberlite Melts in Sills and Pipes

To provide new insights into the evolution of kimberlitic magmas, we have undertaken a detailed petrographic and mineralogical investigation highly evolved carbonate–phlogopite-bearing kimberlites Kepino cluster, Arkhangelsk kimberlite province, Russia. The are represented by volcanoclastic breccias massive macrocrystic units within pipes as well coherent porphyritic sills. from similar in petrography mineral composition to archetypal (Group 1) kimberlite, whereas sills represent that exhibit wide variation amounts carbonate phlogopite. late-stage melts involves increasing oxygen fugacity fluid-phase (forming segregations exsolution, etc.). These processes accompanied transformation primary Al- Ti-bearing phlogopite toward tetraferriphlogopite transition spinel compositions magmatic chromite magnesian ulvöspinel titanomagnetite. Similar emplaced may be transitional carbonatite shallow crust. characterised low reflect fluid degassing process during an explosive emplacement pipes. age, determined 397.3 ± 1.2 Ma, indicates two episodes ultramafic alkaline magmatism first producing non-economic cluster second economic-grade diamondiferous kimberlites.