Olivine from the Namuaiv Pipe, Kola Alkaline Province: the Primary Melt Evolution and Relation to Kimberlite Magmatism

The results of studying olivines in aillikites from the Namuaiv pipe intruded into the Khibiny Massif, the Kola Alkaline Province, are presented. Phenocrysts and xenocrysts are identified among the olivines. The phenocrysts crystallized directly from the primary aillikite melt. The xenocrysts in the Namuaiv aillikites, characterized by high Mg# (0.89–0.91) and elevated Ni and Ti concentrations, are compositionally similar to olivines from kimberlites of the nearby Arkhangelsk diamondiferous province, although they are distinguished by significantly higher Ca contents. These compositional similarities suggest a possible affinity of the primitive melts that gave rise to both the aillikites and the kimberlites. This elevated calcium in the olivines from the Namuaiv aillikites may reflect differences in the metasomatic modification of the mantle source such as the nature of the metasomatic agent (carbonate vs. aqueous fluid) or variations in the degree of its lherzolitization. The differences in the evolutionary trends of the olivines from aillikites and kimberlites can primarily be attributed to the assimilation of lithospheric material (mainly orthopyroxene) during the ascent of kimberlitic melts.