Petrography, geochemistry and strontium isotopic composition of the Mbuji-Mayi and Kundelungu kimberlites (Zaire)

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Authors:Fieremans, M.; Hertogen, J.; Demaiffe, D.
Author Affiliations:Primary:
Univ. Leuven, Lab. Struct. Geol., Louvain, Belgium
Other:
Univ. Libre Bruxelles, Lab. Assoc. Geol.-Petrol., Belgium
Volume Title:Kimberlites; I, Kimberlites and related rocks
Volume Authors:Kornprobst, J., editor
Source:Vol.(11A), p.107-120; Third international kimberlite conference, Clermont-Ferrand, France, Sept., 1982, edited by J. Kornprobst. Publisher: Elsevier Sci. Publ., Amsterdam, Netherlands. ISBN: 0-444-42273-0
Publication Date:1984
Note:In English; illus. incl. 4 tables
Summary:Phenocryst phases in the primary kimberlite nodules at Mbuji-Mayi are two generations of olivine (largely pseudomorphosed to phlogopite and calcite), and Cr-chlorite (often rimmed or replaced by phlogopite). True phlogopite phenocrysts are absent. The very fine-grained matrix consists of Cr-chlorite, hydromica, calcite and accessory amounts of apatite, magnetite and rutile. The Kundelungu kimberlites are of the non-micaceous type (fresh olivine phenocrysts, fine-grained chloritic matrix, no phlogopite phenocrysts); they are much lower in carbonates than the Mbuji-Mayi nodules. The low 87Sr/86Sr initial ratios (0.7040-0.7045) of the Mbuji-Mayi and Kundelungu kimberlites attest to negligible contamination with crustal material. The equally low isotopic ratios of rare carbonate inclusions argue for a cogenetic link with the kimberlites. The Zairean kimberlites are generally similar to other kimberlites with respect to trace-element content: a peculiar feature is the low HREE abundances. The unusually large variations of the La/Th and Th/U ratios of the Mbuji-Mayi primary kimberlite points to important trace-element fractionations by fluid phases at mantle levels. The significantly lower strontium isotopic ratios of Cr-diopside megacrysts at Mbuji-Mayi and Kundelungu seem to rule out a direct genetic link with kimberlites. Nevertheless, these megacrysts apparently crystallized from strongly LREE-enriched liquids. [J.M.H.]
Subjects:Alkaline earth metals; Igneous rocks; Intrusions; Isotopes; Kimberlite; Major elements; Matrix; Metals; Mineral composition; Petrology; Phenocrysts; Pipes; Rare earths; Sr-87/Sr-86; Stable isotopes; Strontium; Textures; Trace elements; Ultramafic composition; Africa; Central Africa; Congo Democratic Republic; Kundelungu Plateau; Mbuji-Mayi; Zaire
Abstract Numbers:85M/4651
Record ID:1984046691
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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