Recycled calcium carbonate is an efficient oxidation agent under deep upper mantle conditions

Observations of high ferric iron content in diamond garnet inclusions and mantle plume melts suggest a highly heterogeneous distribution of ferric iron in the mantle. Recycling of oxidized materials such as carbonates from Earth’s surface by subduction could explain the observed variations. Here we...

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Bibliographic Details
Published in:Communications earth & environment 2021-02, Vol.2 (1), Article 45
Main Authors: Tao, Renbiao, Fei, Yingwei
Format: Article
Language:English
Subjects:
Calcium carbonate
Calcium magnesium silicates
Carbonates
Diamonds
Earth surface
Fayalite
Garnets
Graphite
High temperature effects
Inclusions
Iron
Magnesium
Oxidation
Redox reactions
Slabs
Subduction (geology)
Upper mantle
Valence
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Summary:Observations of high ferric iron content in diamond garnet inclusions and mantle plume melts suggest a highly heterogeneous distribution of ferric iron in the mantle. Recycling of oxidized materials such as carbonates from Earth’s surface by subduction could explain the observed variations. Here we present high-pressure high-temperature multi-anvil experiments to determine the redox reactions between calcium-, magnesium-, or iron-carbonate and ferrous iron-bearing silicate mineral (garnet or fayalite) at conditions representative of subduction zones with intermediate thermal structures. We show that both garnet and fayalite can be oxidized to ferric iron-rich garnets accompanied by reduction of calcium carbonate to form graphite. The ferric iron content in the synthetic garnets increases with increasing pressure, and is correlated with the Ca content in the garnets. We suggest that recycled sedimentary calcium carbonate could influence the evolution of the mantle oxidation state by efficiently increasing the ferric iron content in the deep upper mantle.
ISSN:2662-4435
2662-4435
DOI:10.1038/s43247-021-00116-8