Magmatic Evolution of the Melilitite-Carbonatite-Nephelinite Dyke Series of the Turiy Peninsula (Kandalaksha Bay, White Sea, Russia)

Abstract

Major and trace element data are presented from a suite of INTRODUCTION melilitite–carbonatite–nephelinite dykes, the youngest of three dykes During the last decade, several volumes have outlined swarms in the Turiy peninsula, Russia. The most primitive dykes the progress that has been made in carbonatite research consist of olivine melanephelinites and olivine–melilite mela(Bell, 1989; Egorov, 1991; Bell & Keller, 1995). However, nephelinites that contain high-pressure phases (Cr-diopside and lowcertain problems still remain unresolved. For example, Ca forsteritic olivine). These dykes approximate the composition of what are the petrogenetic relationships between intrusive the parental melt, which probably originated by low-degree partial and volcanic carbonatites? Do carbonatite melts represent melting of metasomatized peridotite. Least-squares mass-balance primary mantle liquids or secondary melts? Are carcalculations and geochemical modelling indicate that differentiation bonatites the products of liquid immiscibility from alkaline was controlled by fractional crystallization involving olivine, clinosilicate melts or do they represent the end products of pyroxene, melilite, Ti-magnetite, apatite, and perovskite. The calfractional crystallization? If carbonatite melts are derived culated modal proportions of the cumulate minerals correspond to by differentiation processes, what were the parental silsome of the rocks seen in alkaline ultramafic plutons elsewhere in icate melts? the Kola peninsula. Calciocarbonatite dykes, with quenched primary Some of these questions can be investigated from the magmatic fabrics, were probably continuously separated by liquid study of the melilitite–carbonatite–nephelinite dyke series immiscibility from an evolved carbonated nepheline melilitite parent. associated with the Turiy complex, Kola (Fig. 1), one of The conjugate silicate liquid to the carbonatitic melt is a melilite several alkaline ultramafic and carbonatite complexes of nephelinite. The distribution of LREE, Zr, Hf, Ta, W, Pb, and the Kola peninsula and northern Karelia (Kukharenko Cu between the carbonatite and melilite nephelinite is in reasonable et al., 1965). One of the main geological features of the agreement with experimental data on element partitioning between Turiy peninsula is the evidence for three distinct episodes alkaline silicate and carbonate melts. of alkaline magmatism. In this paper, the mineralogy and geochemistry of the melilitite–carbonatite–nephelinite dyke series, the youngest of the three groups of dykes at Turiy, are discussed and a quantitative petrogenetic model is proposed for its origin.