ABSTRACT Stable C and O isotope compositions have been compiled for the Kovdor, Sokli, Turiy Mys, Vuoriyarvi, Afrikanda, Khibiny, Sallanlatvi, Telyachiy Island, Tiksheozero and Siilinjärvi Carbonatite Complexes of the Kola-Karelia Region. Stable isotope relationships of various carbonate minerals (calcite, dolomite, rare-earth minerals) from several stages of carbonatite evolution have been investigated in order to determine primary compositions and the influence of secondary processes (Rayleigh fractionation in the fluid-carbonate-silicate system, hydrothermal alteration, degassing, crustal contamination). The phoscorite-carbonatite relationship has also been investigated. The data for some phoscorites (Sokli, Vuoriyarvi) are consistent with an origin by carbonatite-silicate liquid immiscibility, whereas those of the Turiy Mys phoscorites suggest the involvement of different sources. The primary carbon isotope compositions obtained for different complexes show a large variation at fairly constant oxygen isotope compositions. This is best explained by mantle heterogeneity, probably related to CO 2 metasomatism or by removal of a 12 C-enriched phase in the mantle.

ABSTRACT The Afrikanda pluton (Kola Peninsula) comprises predominantly olivine- and clinopyroxene-dominant cumulate ultramafic rocks, with subordinate melteigites and ijolites. On the basis of petrographic and geochemical evidence, these rocks are interpreted to have formed at mid-crustal depths from a Ca-rich melanephelinitic magma. Olivinites (+wehrlites) and clinopyroxenites precipitated from separate batches of magma, whereas the foidolites are related to the clinopyroxenites by crystal fractionation. In both cases, the parental magma was derived by partial melting of a metasomatized lithospheric source enriched in pargasite and phlogopite. The melting occurred just above the amphiboleperidotite solidus, thus producing a liquid depleted in K, Ba and Rb, but enriched in light REE , Nb, Ta and Th. Plutonic carbonatitic rocks occur predominantly as branching veins and nests in the clinopyroxenites. They show variable modal composition in terms of both principal (diopside, magnesiohastingsite and calcite) and minor (perovskite, magnetite, titanite, chlorite and ilmenite) rock-forming phases, delineating a series from calcite-amphibole clinopyroxenite to calcite carbonatite. These rocks crystallized from an alkalisilica-rich carbonatitic magma of mantle provenance. Solidification of this magma and accompanying processes (reaction with the wallrock, xenocryst assimilation, fractionation of a Na-rich fluid, and subsolidus re-equilibration) led to the formation of several distinct parageneses comprising over 50 mineral species.