Olivine From Namuaiy Pipe AIllikite, Kola Alkaline Province: The Primary Melt Evolution and Relation to Kimberlite Magmatism

This study presents petrographic and mineral chemical data for olivine in aillikites from the Namuaiy pipe intruded into the Khibiny Massif, the Kola Alkaline Carbonatite Province. Two distinct olivine populations are identified: phenocrysts and xenocrysts. The phenocrysts crystallized from the aillikite melt, whereas the xenocrysts were entrained from the mantle substrate. Xenocrysts are characterized by high Mg# (0.89–0.91) and elevated concentrations of Ni and Ti, and are compositionally similar to kimberlitic olivines, but differ from them by significantly higher Ca contents. Elevated CaO concentrations in olivines from the aillikites of the Namuaiy pipe may reflect differences in the metasomatic processing of the mantle source (carbonate or aqueous fluid) or the intensity of its lherzolitization. The differences in the evolutionary trends of olivines from aillikites and kimberlites are caused by the assimilation of lithospheric material (mainly orthopyroxene) during the ascent of kimberlitic melts.