Phase Diagrams of Carbonate Materials at High Pressures, with Implications for Melting and Carbon Cycling in the Deep Earth

Litasov, Konstantin D.; Shatskiy, Anton; Podborodnikov, Ivan V.; Arefiev, Anton V.

doi:10.1002/9781119508229.ch14

Cited by 11 publications

(7 citation statements)

References 208 publications

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“…Its pressure–temperature ( P – T ) phase diagram has a range of ambient pressure to 100 GPa. Numerous stable and metastable phases, including CaCO 3 -II, -III, -IIIb, -VI, and -VII, aragonite-II, post-aragonite, CaCO 3 - P 2 1 / c -h, and CaCO 3 - C 222 1 , have been theoretically revealed and experimentally synthesized. − …”

Section: Introductionmentioning

confidence: 99%

Metastable structures of CaCO₃ and their role in transformation of calcite to aragonite and postaragonite

Gavryushkin

Belonoshko

Sagatov

et al. 2020

Crystal Growth & Design

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Using molecular dynamics simulation and evolutionary metadynamic calculations, a series of structures were revealed that possessed enthalpies and Gibbs energies lower than those of aragonite but higher than those of calcite. The structures are polytypes of calcite, differing in the stacking sequence of closepacked (cp) Ca layers. The two-and six-layered polytypes have hexagonal symmetry P6 3 22 and were named hexarag and hexite, respectively. Hexarag is similar to aragonite, but with all the triangles placed on the middle distance between the cp layers. On the basis of the structures found, a two-step mechanism for the transformation of aragonite to calcite is suggested. In the first step, CO 3 triangles migrate to halfway between the Ca layers with the formation of hexarag. In the second step, the two-layered cp (hcp) hexarag structure transforms into three-layered cp (fcc) calcite through a series of many-layered polytypes. The topotactic character of the transformation of aragonite to calcite, with [001] of aragonite being parallel to [0001] of calcite, is consistent with the suggested mechanism. High-temperature X-ray powder diffraction experiments did not reveal hexarag reflections. To assess the possibility of the formation of the polytypes found in nature or experiments, a TEM analysis of ground aragonite was performed. A grain was found that had six superstructure reflections in a direction perpendicular to the plane of the cp layer. This grain is believed to correspond to one of the predicted polytypes, with the diffuse character of the diffraction spots indicating a partial disordering of the cp layer stacking. A topological analysis was also performed, along with energy calculations, of the metastable high-pressure polymorphs CaCO 3 -II, -III, -IIIb, and -VI. The similarity of CaCO 3 -II, -II, and -IIIb to the calcite structure and the small energy difference explain the metastable formation of these polymorphs during the cold compression of calcite. On the basis of the performed analysis, the evolution of the CaCO 3 cation array at calcite to a post-aragonite transformation is described.

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Section: Introductionmentioning

confidence: 99%

Metastable structures of CaCO₃ and their role in transformation of calcite to aragonite and postaragonite

Gavryushkin

Belonoshko

Sagatov

et al. 2020

Crystal Growth & Design

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“…Black and blue lines indicate melting and the aragonite/calcite transition. The purple line shows the aragonite/calcite transition taken from ref . Data for the mantle adiabat and cratonic geotherm are taken from refs and , respectively.…”

Section: Resultsmentioning

confidence: 99%

“…Although the mentioned “calcite-I → calcite-II → calcite-IIIb → calcite-III” phase transitions in CaCO 3 were thoroughly studied both structurally and spectroscopically and the aragonite equation of state (EoS) was constrained throughout its stability field up to 29 GPa and 1673 K, there is a wide gap between the high-temperature boundary of the aragonite stability field and CaCO 3 melting line (Figure ) where neither structures nor properties of thermodynamically stable phases have ever been reported. In a few experimental works, the high-temperature transition of aragonite into a previously unknown phase was studied; the latter was described as “disordered calcite” , “disordered phase” , or “new phase” , , or associated with a low-pressure calcite-V polymorph ( R 3̅ m space group) known to be stable above ∼1240 K at ambient pressure, , and no attempts to reveal any crystal structures, symmetries, or even unit cells have been reported.…”

Section: Introductionmentioning

confidence: 99%

New High-Pressure and High-Temperature CaCO₃ Polymorph

Druzhbin

Rashchenko

Shatskiy

et al. 2022

ACS Earth Space Chem.

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In this work, we report an experimental observation of a new CaCO3 calcite-Vb phase, which occurs as the intermediate between aragonite and calcite-V at pressures >3.5 GPa and temperatures >1200 °C, suggesting it can exist in CaCO3-containing rocks at ∼125–200 km. Calcite-Vb is determined to have the KClO3-type structure with the monoclinic P21/m space group and lattice parameters of a = 6.284(5) Å, b = 4.870(3) Å, c = 3.991(4) Å, β = 107.94(3)°, and V = 116.19(15) Å3. Possible transformation mechanisms between calcite-Vb, aragonite, and calcite-V are illustrated.

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“…The CLIPPIR diamonds are believed to come from such great depth and may derive from metallic liquids. In contrast, oxidized conditions in subducting slabs could provide a very high-pressure environment where crustal-derived carbonates (CaCO3 and MgCO3) might be stable and melt congruently down to depths of the Earth's lower mantle (Litasov et al 2020).…”

Section: Experimental Constraints On Conditions Of Sub-lithospheric D...mentioning

confidence: 99%

Carbonatitic Melts and Their Role in Diamond Formation in the Deep Earth

2021

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Carbonatitic high-density fluids and carbonate mineral inclusions in lithospheric and sub-lithospheric diamonds reveal comparable compositions to crustal carbonatites and, thus, support the presence of carbon-atitic melts to depths of at least the mantle transition zone (~410–660 km depth). Diamonds and high pressure–high temperature (HP–HT) experiments confirm the stability of lower mantle carbonates. Experiments also show that carbonate melts have extremely low viscosity in the upper mantle. Hence, carbonatitic melts may participate in the deep (mantle) carbon cycle and be highly effective metasomatic agents. Deep carbon in the upper mantle can be mobilized by metasomatic carbonatitic melts, which may have become increasingly volumetrically significant since the onset of carbonate subduction (~3 Ga) to the present day.

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Phase Diagrams of Carbonate Materials at High Pressures, with Implications for Melting and Carbon Cycling in the Deep Earth

Cited by 11 publications

References 208 publications

Metastable structures of CaCO₃ and their role in transformation of calcite to aragonite and postaragonite

Metastable structures of CaCO₃ and their role in transformation of calcite to aragonite and postaragonite

New High-Pressure and High-Temperature CaCO₃ Polymorph

Carbonatitic Melts and Their Role in Diamond Formation in the Deep Earth

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Phase Diagrams of Carbonate Materials at High Pressures, with Implications for Melting and Carbon Cycling in the Deep Earth

Cited by 11 publications

References 208 publications

Metastable structures of CaCO3 and their role in transformation of calcite to aragonite and postaragonite

Metastable structures of CaCO3 and their role in transformation of calcite to aragonite and postaragonite

New High-Pressure and High-Temperature CaCO3 Polymorph

Carbonatitic Melts and Their Role in Diamond Formation in the Deep Earth

Contact Info

Product

Resources

About

Metastable structures of CaCO₃ and their role in transformation of calcite to aragonite and postaragonite

Metastable structures of CaCO₃ and their role in transformation of calcite to aragonite and postaragonite

New High-Pressure and High-Temperature CaCO₃ Polymorph