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Russian Geology and Geophysics

2012 year, number 8

THE ALKALINE AND CARBONATITIC ROCKS OF GORNY ALTAI ( Edel'veis сomplex ) AS INDICATORS OF EARLY PALEOZOIC PLUME MAGMATISM IN THE CENTRAL ASIAN FOLD BELT

V.V. Vrublevskiia, V.I. Krupchatnikova, A.E. Izokhb, and I.F. Gertnera
aTomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
bV.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Alkaline magmatism, carbonatites, mantle plume, Central Asian Fold Belt
Pages: 721-735

Abstract

The minor intrusions of the Edel'veis alkaline-carbonatite complex are bounded by the spurs of the North Chuya Ridge in southeastern Gorny Altai. According to Ar-Ar isotope data, the complex formed in the Middle Cambrian (~507 Ma). All of its components (alkali clinopyroxenite-melanogabbro-alkali syenite + Ca-carbonatite) occur in only one pluton. Silicate igneous rocks are equivalent in silica content and alkalinity to potassic alkaline and subalkalic mafic rocks. Apatite-phlogopitic Ca-carbonatites are enriched in P2O5 (up to 3.6 wt.%), Sr (~2500-5500 ppm), and REE (up to ~2000 ppm) and are, presumably, of liquation genesis. A PREMA-type plume component was a predominant magma source for the complex (εNb (Т) = +6.56... +6.85). According to isotope data (87Sr/86Sr(Т) ~ 0.7032-0.7039; δ18 О ~ 7.5-14.9 ‰; δ13 С ~ -2.7...-8.4 ‰), the fractionation of the melts was accompanied by their crustal contamination. The trace-element composition of the rocks suggests that the complex developed on a continental margin and its development was accompanied by late-collisional rifting and the mixing of moderately depleted (PREMA) and enriched suprasubduction lithospheric mantle (EM I or EM II) with continental crust. It is presumed that the alkaline and carbonatite complexes in the western Central Asian Fold Belt are of primary plume origin and form a LIP within this belt together with other associations produced by Early Paleozoic (510-470 Ma) magmatism.