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Abstract <p>In the pelite H<sub>2</sub>O–CO<sub>2</sub> system (2–7 wt % H<sub>2</sub>O and 6–10 wt % CO<sub>2</sub>) at pressures of 3.0–7.8 GPa and temperatures of 900–1090°C, the evolution of the composition of the melt in equilibrium with an eclogite-like association of garnet, phengite, clinopyroxene, coesite, and Fe–Mg calcite was investigated. The experiments modeled the hot subduction of carbonated pelites to depths of 100–240 km. The diamond trap method was used to reconstruct the composition of the melts. With higher <i>PT</i> conditions along the hot subduction geotherm, the composition of the melt evolves from a granite-like silicate to a carbonate-silicate type. The contents of SiO<sub>2</sub> and Al<sub>2</sub>O<sub>3</sub> decrease, while those of CaO and K<sub>2</sub>O increase. The molar ratio of Si/(Ca + Mg&#xa0;+ Fe) in the melt decreases from 40 to 0.5–1.2. The melt formed in the system at 7.8 GPa and 940°C is most enriched in carbonate. At 5.5 GPa and 1030°C, the carbonate-silicate melt coexists with a silicate melt. It is concluded that an increase in H<sub>2</sub>O content from 1 to 2–7 wt % leads to the formation of a volatile-rich carbonate-silicate melt rather than a carbonatitic one in the pelite H<sub>2</sub>O–CO<sub>2</sub> system at pressures ranging from 5.5 to 7.8 GPa. In terms of SiO<sub>2</sub> and alkalis content, this melt resembles primary kimberlitic melts but contains too much CaO. The generation and subsequent migration of such melts could make a substantial contribution to deep carbon and water cycles if the subducting carbonated pelites are additionally heated due to delamination at the slab–mantle wedge boundary, during the convective capture into the mantle wedge, or under overall stagnation of slabs.</p>

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Melting of Carbonated Pelites at PT Conditions of Hot Subduction: Results of Diamond Trap Experiments

  • 期刊论文

  • 发表日期：

    2026年7月11日

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  • A. G. Sokol,
  • A. N. Kruk,
  • O. A. Kozmenko

摘要

Abstract

In the pelite H2O–CO2 system (2–7 wt % H2O and 6–10 wt % CO2) at pressures of 3.0–7.8 GPa and temperatures of 900–1090°C, the evolution of the composition of the melt in equilibrium with an eclogite-like association of garnet, phengite, clinopyroxene, coesite, and Fe–Mg calcite was investigated. The experiments modeled the hot subduction of carbonated pelites to depths of 100–240 km. The diamond trap method was used to reconstruct the composition of the melts. With higher PT conditions along the hot subduction geotherm, the composition of the melt evolves from a granite-like silicate to a carbonate-silicate type. The contents of SiO2 and Al2O3 decrease, while those of CaO and K2O increase. The molar ratio of Si/(Ca + Mg + Fe) in the melt decreases from 40 to 0.5–1.2. The melt formed in the system at 7.8 GPa and 940°C is most enriched in carbonate. At 5.5 GPa and 1030°C, the carbonate-silicate melt coexists with a silicate melt. It is concluded that an increase in H2O content from 1 to 2–7 wt % leads to the formation of a volatile-rich carbonate-silicate melt rather than a carbonatitic one in the pelite H2O–CO2 system at pressures ranging from 5.5 to 7.8 GPa. In terms of SiO2 and alkalis content, this melt resembles primary kimberlitic melts but contains too much CaO. The generation and subsequent migration of such melts could make a substantial contribution to deep carbon and water cycles if the subducting carbonated pelites are additionally heated due to delamination at the slab–mantle wedge boundary, during the convective capture into the mantle wedge, or under overall stagnation of slabs.