GEOCHEMISTRY AND PETROGENESIS OF THE MELILITITE-NEPHELINITE-CARBONATITE DYKE SERIES OF TURIY PENINSULA (KANDALAKSHA GULF OF THE WHITE SEA)

摘要

The paper summarizes the new data on geochemistry of the melilitine-hephelinite-carbonatite dyke series of Turiy peninsula. Olivine and olivine-melilitic melanephelinites representing the first generation of dykes are supposed to be close in composition to the primary melts originated from the low degree melting of a carbonatized mantle peridotite at the depth of 75-80 km. Quantitative mineralogical- geochemical modelling shows the leading role of a fractional crystallization while the initial melt differentiation process, with participation of olivine, a clinopyroxen of varying composition, melilite, titanomagnetite, apatite and perovskite. The calcite carbonatite dykes, with quenched primary magmatic fabrics of endocontact zones, have the composition which is closely similar to the world-mean calcite carbonatite. The dyke carbonatites are supposed to be derived by a liquid immiscibility from a melilite-nephelinite melt enriched in CO_2, with segregation of about 5 percent of the Ca-rich carbonate liquid. Distribution of LREE, Zr, Hf, Ta, W, Pb and Cu in the co-existing carbonatites and melilite nephelinites corresponds to experimental data on behaviour of these elements within the 《alkaline silicate melt- carbonatite melt》 system.