The Importance of redox reactions in fluid transport systems in the Earth's deep mantle: evidence from nano-inclusions

Dorrit Jacob, Richard Wirth, Larissa Dobrzhinetskaya

    Research output: Contribution to conferenceAbstract


    Focused Ion beam assisted TEM studies of inclusions in diamond have opened up a new perspective on the Earth’s deep mantle processes. They enabled direct observation of fluids and have shown a large chemical and redox heterogeneity at the submicron scale, which is not observed in micron-sized inclusions. While crustal metamorphic diamonds are generally formed under oxidizing conditions, polycrystalline diamonds from the Earth's mantle and carbonado have inclusion suites reflecting variable, and sometimes extreme, redox conditions. Diamond fluid compositions, however, fall in the same compositional field for worldwide diamond fluids, regardless of their geodynamic environment. They conform with the fluid end-members established by studies on fibrous diamonds, suggesting a universally important role of a limited number of basic ingredients, namely carbonates, silicates, halides and water. Strong redox gradients reflected by the micro-inclusions indicate diamond precipitation via small-scale, ephemeral redox processes driven by the contrasting oxidation states of fluids and their depositional environment. The susceptibility of the melting point of mantle rocks to the presence of even small amounts of volatiles promotes melting simultaneous to diamond precipitation, which is further enhanced by the changing of fluid composition towards higher water activity. This creates a chemically heterogeneous environment, in which diamonds and their inclusions are precipitated via redox-freezing processes.
    Original languageEnglish
    Number of pages1
    Publication statusPublished - 2014
    EventAmerican Geophysical Union Fall Meeting - San Francisco
    Duration: 15 Dec 201419 Dec 2014


    ConferenceAmerican Geophysical Union Fall Meeting
    CitySan Francisco


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