Carbonated mantle domains at the base of the Earth's transition zone

Wei dong Sun*, Chris J. Hawkesworth, Chao Yao, Chan chan Zhang, Rui fang Huang, Xi Liu, Xin lei Sun, Trevor Ireland, Mao shuang Song, Ming xing Ling, Xing Ding, Zhao feng Zhang, Wei ming Fan, Zhong qing Wu

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    26 Citations (Scopus)

    Abstract

    The oxygen fugacity of the upper mantle is 3–4 orders of magnitude higher than that of the lower mantle and this has been attributed to Fe2 + disproportionating into Fe3 + plus Fe0 at pressures > 24 GPa. The upper mantle might therefore have been expected to have evolved to more oxidizing compositions through geological time, but it appears that the oxygen fugacity of the upper mantle has remained constant for the last 3.5 billion years. Thus, it indicates that the mantle has been actively buffered from the accumulation of Fe3 +, and that this is linked to oxidation of diamond to carbonate coupled with reduction of Fe3 + to Fe2 +. When subducted plates penetrate into the lower mantle, compensational upwelling transports bridgmanite into the transition zone, where it breaks down to ringwoodite and majorite, releasing the ferric iron. The system returns to equilibrium through oxidation of diamond. Early in Earth history, diamond may have been enriched at the base of the transition zone in the Magma Ocean, because it is denser than peridotite melts at depths shallower than 660 km, and it is more buoyant below. Ongoing oxidation of diamond forms carbonate, leading to relatively high carbonate concentrations in the source of ocean island basalts.

    Original languageEnglish
    Pages (from-to)69-75
    Number of pages7
    JournalChemical Geology
    Volume478
    DOIs
    Publication statusPublished - 5 Feb 2018

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