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<p>CaCO<sub>3</sub> is one of the most abundant carbonates at the Earth’s surface. It is transported into the mantle in substantial quantities via subducted slabs and participates in the deep mantle carbon cycle along with other mantle materials. Our experiments utilized the CaCO<sub>3</sub>–Fe–SiO<sub>2</sub> system to simulate the environment of subducted oceanic crust entering the deep mantle. In situ X-ray diffraction experiments were performed on the CaCO<sub>3</sub>–Fe–SiO<sub>2</sub> system at pressures of 25–53 GPa and temperatures of 1200–2250&#xa0;K using a laser-heated diamond anvil cell. The results indicate that redox reactions occur within the pressure range of 25–53 GPa and the temperature range of 1500–2000&#xa0;K, leading to the formation of CaSiO<sub>3</sub> + FeO + Fe<sub>3</sub>C. At higher temperatures of 2000–2250&#xa0;K and pressures of 25–53 GPa, the products are CaSiO<sub>3</sub> + Fe<sub>3</sub>O<sub>4</sub> + Fe<sub>7</sub>C<sub>3</sub>. The mineral assemblage of Fe<sub>3</sub>O<sub>4</sub> and Fe<sub>7</sub>C<sub>3</sub>, crystallizing under temperature conditions corresponding to the slab-mantle interface, can be encapsulated as inclusions in superdeep diamonds, such as those from the Juina area of Brazil. This assemblage may serve as an indicator of diamond formation at depths of approximately 700–1300&#xa0;km in the deep mantle.</p>

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Redox reactions in subducted CaCO3–Fe–SiO2 as a potential source of superdeep diamond inclusions

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月25日

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  • Mengqi Guo,
  • Xinyang Li,
  • Zhu Mao,
  • Fangfei Li,
  • Liang Li,
  • Qiang Zhou

摘要

CaCO3 is one of the most abundant carbonates at the Earth’s surface. It is transported into the mantle in substantial quantities via subducted slabs and participates in the deep mantle carbon cycle along with other mantle materials. Our experiments utilized the CaCO3–Fe–SiO2 system to simulate the environment of subducted oceanic crust entering the deep mantle. In situ X-ray diffraction experiments were performed on the CaCO3–Fe–SiO2 system at pressures of 25–53 GPa and temperatures of 1200–2250 K using a laser-heated diamond anvil cell. The results indicate that redox reactions occur within the pressure range of 25–53 GPa and the temperature range of 1500–2000 K, leading to the formation of CaSiO3 + FeO + Fe3C. At higher temperatures of 2000–2250 K and pressures of 25–53 GPa, the products are CaSiO3 + Fe3O4 + Fe7C3. The mineral assemblage of Fe3O4 and Fe7C3, crystallizing under temperature conditions corresponding to the slab-mantle interface, can be encapsulated as inclusions in superdeep diamonds, such as those from the Juina area of Brazil. This assemblage may serve as an indicator of diamond formation at depths of approximately 700–1300 km in the deep mantle.