On the formation of element carbon during decomposition of CaCO3 at High P-T parameters under reducing conditions

Chepurov, A. I.; Сонин, В. М.; Жимулев, Е. И.; Томиленко, А. А.

doi:10.1134/s1028334x11120233

Cited by 22 publications

(5 citation statements)

References 9 publications

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“…Even at this initial stage, the face of a diamond acquires a relief with an average height of more than 3 µm (Fig. 3c), whereas high-quality as-grown synthetic HPHT diamond crystals usually have a surface roughness of less than 5 nm (Chepurov et al, 2018a). Since several such pyramids formed on the faces of the crystal, after a certain time of growth, the face of a diamond crystal splits into several seg- Figure 5.…”

Section: Morphology Of Diamond Crystals Grown On Seed Crystals In a Mmentioning

confidence: 99%

How do diamonds grow in metal melt together with silicate minerals? An experimental study of diamond morphology

Сонин

Dereppe²,

Жимулев

et al. 2020

Eur. J. Mineral.

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Abstract. The origin and evolution of metal melts in the Earth's mantle and their role in the formation of diamond are the subject of active discussion. It is widely accepted that portions of metal melts in the form of pockets can be a suitable medium for diamond growth. This raises questions about the role of silicate minerals that form the walls of these pockets and are present in the volume of the metal melt during the growth of diamonds. The aim of the present work was to study the crystallization of diamond in a complex heterogeneous system: metal-melt–basalt–carbon. The experiments were performed using a multianvil high-pressure apparatus of split-sphere type (BARS) at a pressure of 5.5 GPa and a temperature of 1500 ∘C. The results demonstrated crystallization of diamond in metal melt together with garnet and clinopyroxene, whose chemical compositions are similar to those of eclogitic inclusions in natural diamond. We show that the presence of silicates in the crystallization medium does not reduce the chemical ability of metal melts to catalyze the conversion of graphite into diamond, and, morphologically, diamond crystallizes mainly in the form of a cuboctahedron. When the content of the silicate material in the system exceeds 5 wt %, diamond forms parallel-growth aggregates, but 15 wt % of silicate phases block the crystallization chamber, preventing the penetration of metallic melt into them, thus interrupting the growth of diamond. We infer that the studied mechanism of diamond crystallization can occur at lower-mantle conditions but could also have taken place in the ancient continental mantle of the Earth, under reducing conditions that allowed the stability of Fe–Ni melts.

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Section: Morphology Of Diamond Crystals Grown On Seed Crystals In a Mmentioning

confidence: 99%

How do diamonds grow in metal melt together with silicate minerals? An experimental study of diamond morphology

Сонин

Dereppe²,

Жимулев

et al. 2020

Eur. J. Mineral.

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“…The experiments were carried out at pressures 5.5–6.0 GPa and temperatures 1350–1400 °C with duration over 45 h in the diamond stability field 56 . The details of the procedure are described in 11 , 15 , 57 . The measurement errors were ± 0.2 GPa and ± 25 °C.…”

Section: Methodsmentioning

confidence: 99%

The composition of the fluid phase in inclusions in synthetic HPHT diamonds grown in system Fe–Ni–Ti–C

Сонин

Томиленко

Жимулев

et al. 2022

Sci Rep

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Diamonds grown by high pressure high temperature process (HPHT) are usually characterized by yellow color and high contents of nitrogen. Introduction of Ti decreases nitrogen content in diamond. Understanding the formation of nitrogen-poor diamond is very important not for the progress of HPHT process only, but because these diamond varieties represent the rare natural stones, although their crystallization conditions have not been clarified yet. Here we studied the composition of fluid phase in synthetic diamonds. The experiments were performed using a high-pressure apparatus BARS at pressures 5.5–6.0 GPa and temperatures 1350–1400 °C. It was found that introduction of metallic Ti leads to concentration of nitrogen mainly as nitrogenated hydrocarbons. The hypothesis that elucidates the formation of low-nitrogen diamond in Fe–Ni is proposed: the presence of Ti leads to an increase of hydrogen fugacity in the metal melt which drastically reduces the nitrogen solubility. As a result, nitrogen concentrates in the form of complex hydrocarbon compounds, while diamond grows colorless and characterized by very low nitrogen content. It is suggested that the proposed mechanism acts the same way in the presence of other metals which are strong reducing agents.

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“…In comparison with MgCO 3 , CaCO 3 reacting with Fe 0 proceeded much slower. For CaCO 3 -Fe 0 coupling in closed systems, Ca-wüstites were identified after reactions at 3-5.5 GPa and 1573-1673 K (5-48 h) with solid carbon in the form of graphite (Chepurov et al, 2011). Similarly for deeper subduction geotherms, interaction of CaCO 3 -Fe 0 system at 4-16 GPa and 923-1673 K was established as (Martirosyan et al, 2016):…”

Section: Carbonates Reduction By Reduced Mantlementioning

confidence: 99%

Fate of Carbonates in the Earth’s Mantle (10-136 GPa)

Gao

Yuan

et al. 2022

Front. Earth Sci.

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Earth carbon cycle shapes the evolution of our planet and our habitats. As a key region of carbon cycle, subduction zone acts as a sole channel transporting supracrustal carbonate rocks down to the mantle, balancing carbon budget between the Earth’s surface and the interior, and regulating CO2 concentration of the atmosphere. How carbonates evolve at depth is thus, a most fundamental issue in understanding carbon flux and carbon sequestration mechanism in the Earth. This study reviews prominent progresses made in the field of crystal chemistry of carbonates along subduction geotherms. It clearly finds that, in addition to common carbonates in the Earth’s crust, several new polymorphs of carbonates have been discovered to be stable under high-pressure and high-temperature conditions. This opens possibilities for oxidized carbon species in the deep Earth. However, metamorphic decarbonatation and reduction reactions restrict subducting carbonates to the top-mid region of the lower mantle. Specifically, subsolidus decarbonatation in the form of carbonates reacting with silicates has been proposed as an efficient process releasing CO2 from slabs to the mantle. Besides, carbonate reduction in the metal-saturated mantle likely results in generation of super-deep diamonds and a considerable degree of carbon isotope fractionation. Review of these novel findings leads us to consider three issues in the further studies, including 1) searching for new chemical forms of carbon in the mantle, 2) determining the reduction efficiency of carbonates to diamonds and the accompanying carbon isotope fractionation and 3) concerning carbon cycle in subduction of continental crust.

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On the formation of element carbon during decomposition of CaCO3 at High P-T parameters under reducing conditions

Cited by 22 publications

References 9 publications

How do diamonds grow in metal melt together with silicate minerals? An experimental study of diamond morphology

How do diamonds grow in metal melt together with silicate minerals? An experimental study of diamond morphology

The composition of the fluid phase in inclusions in synthetic HPHT diamonds grown in system Fe–Ni–Ti–C

Fate of Carbonates in the Earth’s Mantle (10-136 GPa)

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