Magmatic evolution of the differentiated ultramafic, alkaline and carbonatite intrusion of Vuoriyarvi (Kola Peninsula, Russia). A LA-ICP-MS study of apatite

The nature of the petrogenetic links between carbonatites and associated silicate rocks is still under discussion (i.e., [Gittins J., Harmer R.E., 2003. Myth and reality of the carbonatite–silicate rock “association”. Period di Mineral. 72, 19–26.]). In the Paleozoic Kola alkaline province (NW Russia), the carbonatites are spatially and temporally associated to ultramafic cumulates (clinopyroxenite, wehrlite and dunite) and alkaline silicate rocks of the ijolite–melteigite series [Kogarko, L.N., 1987. Alkaline rocks of the eastern part of the Baltic Shield (Kola Peninsula). In: Fitton, J.G., and Upton, B.G.J. (eds). Alkaline igneous rocks. Geol. Soc. Special Publication 30, 531–544; Kogarko, L.N., Kononova, V.A., Orlova, M.P., Woolley, A.R., 1995. Alkaline rocks and carbonatites of the world. Part 2. Former USSR. Chapman and Hall, London, 225 pp; Verhulst, A., Balaganskya, E., Kirnarsky, Y., Demaiffe, D., 2000. Petrological and geochemical (trace elements and Sr–Nd isotopes) characteristics of the Paleozoic Kovdor ultramafic, alkaline and carbonatite intrusion (Kola Peninsula, NW Russia). Lithos 51, 1–25; Dunworth, E.A., Bell, K., 2001. The Turiy Massif, Kola Peninsula, Russia; isotopic and geochemical evidence for a multi-source evolution. J. Petrol. 42, 377–405; Woolley, A.R., 2003. Igneous silicate rocks associated with carbonatites: their diversity, relative abundances and implications for carbonatite genesis. Period. di Mineral. 72, 9–17)]. In the small (≈ 20 km2) Vuoriyarvi massif, apatite is typically a liquidus phase during the magmatic evolution and so it can be used to test genetic relationships. Trace elements contents have been obtained for both whole rocks and apatite (by LA-ICP-MS). The apatites define a single continuous chemical evolution marked by an increase in REE and Na (belovite-type of substitution, i.e., 2Ca2+ = Na+ + REE3+). This evolution possibly reflects a fractional crystallisation process of a single batch of isotopically homogeneous, mantle-derived magma. The distribution of REE between apatite and their host carbonatite have been estimated from the apatite composition of a carbonatite vein, belonging to the Neskevara conical-ring-like vein system. This carbonatite vein is tentatively interpreted as a melt. So, the calculated distribution coefficients are close to partition coefficients. Rare earth elements are compatible in apatite (D > 1) with a higher compatibility for the middle REE (DSm : 6.1) than for the light (DLa : 4.1) and the heavy (DYb : 1) REE.