Abyssal tholeiites from the Oceanographer Fracture Zone - I. Petrology and fractionation

Tsugio Shibata, Stephen E. DeLong, David Walker

    Research output: Contribution to journalArticle

    50 Citations (Scopus)

    Abstract

    Fresh basalts from the Oceanographer Fracture Zone are petrographically and chemically similar to typical abyssal tholeiites, but are somewhat enriched in large ion lithophile elements, with consistent differences among separate dredge hauls. Olivine compositions are in equilibrium with host basalt for reasonable KDvalues, but some plagioclases are anomalously calcic (e.g., a rock highly differentiated in Mg/Mg+Fe bears some plagioclase of An86). Ti/Al in clinopyroxene is approximately constant at 1/6, but Ti+Al abundance decreases in the sequence basalt groundmass cpx, basalt phenocryst+microphenocryst cpx, gabbro cpx (samples from adjacent dredges), an effect that may be related to decrease in cooling rate. Least-squares calculations indicate that 45% of magma with the composition of the more primitive sample must be removed as plagioclase, clinopyroxene and olivine (in the ratio 4.4:2.7:1, respectively) to obtain the composition of the more differentiated sample. Both samples have excess plagioclase on the liquidus, however, which should not be the case for the differentiated composition if it is produced by fractionation of all three phases. The excess of plagioclase and the anomalous plagioclase compositions indicate that the samples cannot be related solely by fractional crystallization. Additional processes such as magma mixing or plagioclase accumulation (or both) must have effected these differences.

    Original languageEnglish
    Pages (from-to)89-102
    Number of pages14
    JournalContributions to Mineralogy and Petrology
    Volume70
    Issue number1
    DOIs
    Publication statusPublished - Mar 1979

    Fingerprint

    Petrology
    petrology
    plagioclase
    Fractionation
    fracture zone
    fractionation
    basalt
    Chemical analysis
    Dredges
    dredger
    olivine
    clinopyroxene
    magma
    gabbro
    phenocryst
    liquidus
    Crystallization
    bears
    Heavy ions
    fractional crystallization

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology

    Cite this

    Abyssal tholeiites from the Oceanographer Fracture Zone - I. Petrology and fractionation. / Shibata, Tsugio; DeLong, Stephen E.; Walker, David.

    In: Contributions to Mineralogy and Petrology, Vol. 70, No. 1, 03.1979, p. 89-102.

    Research output: Contribution to journalArticle

    Shibata, Tsugio ; DeLong, Stephen E. ; Walker, David. / Abyssal tholeiites from the Oceanographer Fracture Zone - I. Petrology and fractionation. In: Contributions to Mineralogy and Petrology. 1979 ; Vol. 70, No. 1. pp. 89-102.
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