The dunitic mantle-crust transition zone in the Oman ophiolite: Residue of melt-rock interaction, cumulates from high-mgo melts, or both?

Bénédicte Abily*, Georges Ceuleneer

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    47 Citations (Scopus)

    Abstract

    The contact between mantle peridotite and gabbro from the lower oceanic crust is usually underlined by a horizon of dunite. The origin of this dunitic transition zone (DTZ) is still debated. It is viewed either as a pile of cumulus olivine from high-MgO melts, or as former mantle peridotite pervasively percolated by melts undersaturated with pyroxene (e.g., as mid-oceanic ridge basalts [MORBs] at low pressure), and transformed into dunite. We show that the two hypotheses are not mutually exclusive, although they do not account for the same parts of the DTZ. We determined a petrological profi le through a 330-m-thick DTZ that developed at the top of a mantle diapir in the Oman ophiolite. The lowermost 280 m have a reactional origin: olivine and Cr-spinel record the complex percolation and interaction history between mantle peridotite and MORB. In the uppermost 50 m, chemical trends become consistent with a cumulus origin of the dunite, olivine crystallization being a prelude to the crystallization of the overlying gabbros. The DTZ develops largely in response to melt-rock reaction, consistent with the "reactive fi lter" hypothesis, but the proportion of cumulate dunite is high enough to require parent melts with a signifi cantly higher Mg content than the most primitive MORB erupted on the seafl oor.

    Original languageEnglish
    Pages (from-to)67-70
    Number of pages4
    JournalGeology
    Volume41
    Issue number1
    DOIs
    Publication statusPublished - Jan 2013

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