MINERALOGY OF THE MELILITITE-NEPHELINITE-CARBONATITIC DYKE SERIES ROCKS FROM TURIY PENINSULA (KANDALAKSHA GULF OF THE WHITE SEA)

摘要

The later group of dykes developed over the Turiy peninsula complex forms the following evolutionary row of rocks: olivine and olivine-melilite melanephelinite- olivine- nepheline melilitite-nepheline melilitite- melilite nephelinite- carbonatite- nephelinite. The first generation dykes are suggested to be closest to the initial melt composition; they contain such high baric xenocrysts as Cr-diopside and low-Ca forsterite, representing, probably, the mantle xenoliths desintegration products. Phenocrysts and matrix phases include Ca-bearing olivine, clinopyroxene of varying composition, Na-akermanite melilite, biotite, kaersutite, nepheline, nosean, sanidine, analcimes, titanomagnetite, ilmenite, perovskite, Ti-garnet. Crystallization temperatures for olivine and clinopyroxene (1250-1300 deg C) were determined by mineral-liquid equilibrum and appeared to be similar to the experimental liquidus temperatures for natural olivine melanephelinites (H. Yoder, C. Tilley, 1962). Wide varieties of clinopyroxenes composition (as a function of the rock mafic index, as well as within a single zonal phenocryst)- from diopside- hedenbergite enriched in Ti and Al up to aegirine and aegirine-augite- indicate a complex polybaric fractionation of the primary olivine-melilite melanephelinite melt, initial one for the Turiy peninsula dyke series.