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Natural diamond formation by self-redox of ferromagnesian carbonate.

ABSTRACT: Formation of natural diamonds requires the reduction of carbon to its bare elemental form, and pressures (P) greater than 5 GPa to cross the graphite-diamond transition boundary. In a study of shocked ferromagnesian carbonate at the Xiuyan impact crater, we found that the impact pressure-temperature (P-T) of 25-45 GPa and 800-900 °C were sufficient to decompose ankerite Ca(Fe²⁺,Mg)(CO₃)₂ to form diamond in the absence of another reductant. The carbonate self-reduced to diamond by concurrent oxidation of Fe²⁺ to Fe³⁺ to form a high-P polymorph of magnesioferrite, MgFe³⁺₂O₄ Discovery of the subsolidus carbonate self-reduction mechanism indicates that diamonds could be ubiquitously present as a dominant host for carbon in the Earth's lower mantle.

SUBMITTER: Chen M

PROVIDER: S-EPMC5856551 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Natural diamond formation by self-redox of ferromagnesian carbonate.

Chen Ming M Shu Jinfu J Xie Xiande X Tan Dayong D Mao Ho-Kwang HK

Proceedings of the National Academy of Sciences of the United States of America 20180226 11

Formation of natural diamonds requires the reduction of carbon to its bare elemental form, and pressures (P) greater than 5 GPa to cross the graphite-diamond transition boundary. In a study of shocked ferromagnesian carbonate at the Xiuyan impact crater, we found that the impact pressure-temperature (P-T) of 25-45 GPa and 800-900 °C were sufficient to decompose ankerite Ca(Fe2+,Mg)(CO3)2 to form diamond in the absence of another reductant. The carbo ...[more]

PMID: 29483248

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