Science Links Japan | Sr, Nd, C and O isotopic compositions of carbonatite and peralkaline silicate rocks from the Zhidoy complex, Russia. Evidence for binary mixing, liquid immiscibility and a heterogeneous depleted mantle source region.

Sr, Nd, C and O isotopic compositions of carbonatite and peralkaline silicate rocks from the Zhidoy complex, Russia. Evidence for binary mixing, liquid immiscibility and a heterogeneous depleted mantle source region.

Accession number;01A0273659

Title;Sr, Nd, C and O isotopic compositions of carbonatite and peralkaline silicate rocks from the Zhidoy complex, Russia. Evidence for binary mixing, liquid immiscibility and a heterogeneous depleted mantle source region.

Author; MORIKIYO T (Shinshu Univ., Matsumoto, Jpn) TAKANO K (Shinshu Univ., Matsumoto, Jpn) MIYAZAKI T (Niigata Univ., Niigata, Jpn) KAGAMI H (Niigata Univ., Niigata, Jpn) VLADYKIN N V (Vinogradov Inst. Geochemistry, Russian Acad. Sci., Irkutsk, Rus)

Journal Title;J Mineral Petrol Sci

Journal Code:G0150B

ISSN:1345-6296

VOL.95;NO.7;PAGE.162-172(2000)

Figure&Table&Reference;FIG.10, TBL.4, REF.18

Pub. Country;Japan

Language;English

Abstract;Sr, Nd, C and O isotopic compositions were determined for carbonatite and associated peralkaline silicate rocks from the Zhidoy complex in the East Sayan province, Russia. The complex consists predominantly of alkali pyroxenite with a small amount of ijolite, nepheline syenite and carbonatite. Rb-Sr isotopic data for two carbonatite samples, ijolite, and nepheline syenite give a whole rock isochron age of 569 Ma with initial .EPSILON.Sr and .EPSILON.Nd values of about -6.1 and 1.1, respectively. This indicates that the rocks were derived from a single parental magma by magmatic differentiation. Judging from the mode of occurrence, it is presumed that the carbonatites were produced by carbonate-silicate liquid immiscibility. Another two carbonatite samples have .EPSILON.Sr and .EPSILON.Nd values of -9.3 and -11.8, 2.3 and 3.4, respectively. They show a wide range of variation in initial .EPSILON.Sr and .EPSILON.Nd values. The concentration of Sr in the rock varies from 4660 to 13600 ppm. The chemical and isotopic variations in the carbonatite are not due to crustal contamination but are the result of the mixing of two different carbonatitic components. It is concluded that alkaline magmatism occurred at least twice in the Zhidoy area: (1) the first magmatism produced the alkali pyroxenite cumulate and the carbonatite with low initial 87Sr/86Sr ratio; (2) the second one produced the ijolite, nepheline syenite and high-.EPSILON.Sr carbonatite. The generation of magmas with different 87Sr/86Sr and 143Nd/144Nd ratios may reflect an isotopic heterogeneity of the mantle source region. (author abst.)

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