Mantle metasomatism—precursor to continental alkaline volcanism

Suzanne Y. Wass*, N. W. Roge

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    121 Citations (Scopus)

    Abstract

    REE distributions of an unusual suite of mantle-derived amphibole/apatite rich xenoliths have very steep, LREE-enriched chondrite-normalised patterns with no Eu anomalies. These are closely analogous to REE distributions of carbonatitic and kimberlitic rocks. A wide range in absolute abundances of REE reflects the varied mineral assemblages of this xenolith suite and, together with other trace element and volatile concentrations, supports an origin by fractionation of, or separation from, a volatile-charged LIL-enriched (possibly kimberlitic/carbonatitic) magma. Such a magma could be a medium for volatile transfer, addition of Ti, V, K and P, and LREE enrichment within the upper mantle. It is postulated that such metasomatism in the upper mantle is a necessary precursor to continental alkaline volcanism. Geochemical modelling based on REE suggests that a pyrolite source +0.35% apatite (total of 0.5% apatite), with amphibole accounting for all K2O, can yield basanitic liquids with approximately 1–10% partial melting if the source is LREE-enriched (La about 20 times chondrite and Yb about 4.5–5 times chondrite). REE and trace element contents of the host rocks indicate that little exchange of these elements has occurred between xenolith and host magma during transport and emplacement.

    Original languageEnglish
    Pages (from-to)1811-1823
    Number of pages13
    JournalGeochimica et Cosmochimica Acta
    Volume44
    Issue number11
    DOIs
    Publication statusPublished - Nov 1980

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