The geochemistry of ultramafic to mafic volcanics from the belingwe greenstone belt, Zimbabwe: Magmatism in an archean continental large igneous province

Kenji Shimizu, Eizo Nakamura, Shigenori Maruyama

    Research output: Contribution to journalArticlepeer-review

    47 Citations (Scopus)

    Abstract

    The evolution of the late Archean Belingwe greenstone belt, Zimbabwe, is discussed in relation to the geochemistry of the ultramafic to mafic volcanic rocks. Four volcanic types (komatiite, komatiitic basalt, D-basalt and E-basalt) are distinguished in the 2.7 Ga Ngezi volcanic sequence using a combination of petrography and geochemistry. The komatiites and D-basalts are rocks in which isotopic systems and trace elements are depleted. Chemical variations in komatiites and D-basalts can be explained by fractional crystallization from the parental komatiite. In contrast, komatiitic basalts and E-basalts are siliceous and display enriched isotopic and trace element compositions. Their chemical trends are best explained by assimilation with fractional crystallization (AFC) from the primary komatiite. AFC calculations indicate that the komatiitic basalts and E-basalts are derived from komatiites contaminated with ∼20% and ∼30% crustal material, respectively. The volcanic stratigraphy of the Ngezi sequence, which is based on field relationships and the trace element compositions of relict clinopyroxenes, shows that the least contaminated komatiite lies between highly contaminated komatiitic basalt flows, and has limited exposure near the base of the succession. Above these flows, D- and E-basalts alternate. The komatiite appears to have erupted on the surface only in the early stages, when plume activity was high. As activity decreased with time, komatiite magmas may have stagnated to form magma chambers within the continental crust. Subsequent komatiitic magmas underwent fractional crystallization and were contaminated with crust to form D-basalts or E-basalts.

    Original languageEnglish
    Pages (from-to)2367-2394
    Number of pages28
    JournalJournal of Petrology
    Volume46
    Issue number11
    DOIs
    Publication statusPublished - Nov 2005

    Keywords

    • Belingwe greenstone belt
    • Continental flood basalt
    • Crustal assimilation
    • Komatiite
    • Plume magmatism

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology

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