Graphite to diamond transformation during sediment–peridotite interaction at 7.5 and 10.5 GPa

Гирнис, А. В.; Brey, Gerhard P.; Bulatov, Vasily V.; Höfer, Heidi E.; Woodland, Alan B.

doi:10.1016/j.lithos.2018.04.010

Cited by 8 publications

(4 citation statements)

References 50 publications

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“…It is generally accepted that most diamonds were crystallized at the base of ancient cratons at 5-7 GPa and 900-1400 • C [56] since Archean, whereas the carbonatitic melts are considered as the most probable carbon source and medium for their crystallization [27,28,57,58], while other media for diamond crystallization are also known [59][60][61][62][63].…”

Section: Variety Of Carbonates In Diamonds and Their Originmentioning

confidence: 99%

The K2CO3–CaCO3–MgCO3 System at 6 GPa: Implications for Diamond Forming Carbonatitic Melts

et al. 2019

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Carbonate micro inclusions with abnormally high K2O appear in diamonds worldwide. However, the precise determination of their chemical and phase compositions is complicated due to their sub-micron size. The K2CO3–CaCO3–MgCO3 is the simplest system that can be used as a basis for the reconstruction of the phase composition and P–T conditions of the origin of the K-rich carbonatitic inclusions in diamonds. In this regard, this paper is concerned with the subsolidus and melting phase relations in the K2CO3–CaCO3–MgCO3 system established in Kawai-type multianvil experiments at 6 GPa and 900–1300 °C. At 900 °C, the system has three intermediate compounds K2Ca3(CO3)4 (Ca# ≥ 97), K2Ca(CO3)2 (Ca# ≥ 58), and K2Mg(CO3)2 (Ca# ≤ 10), where Ca# = 100Ca/(Ca + Mg). Miscibility gap between K2Ca(CO3)2 and K2Mg(CO3)2 suggest that their crystal structures differ at 6 GPa. Mg-bearing K2Ca(CO3)2 (Ca# ≤ 28) disappear above 1000 °C to produce K2Ca3(CO3)4 + K8Ca3(CO3)7 + K2Mg(CO3)2. The system has two eutectics between 1000 and 1100 °C controlled by the following melting reactions: K2Ca3(CO3)4 + K8Ca3(CO3)7 + K2Mg(CO3)2 → [40K2CO3∙60(Ca0.70Mg0.30)CO3] (1st eutectic melt) and K8Ca3(CO3)7 + K2CO3 + K2Mg(CO3)2 → [62K2CO3∙38(Ca0.73Mg0.27)CO3] (2nd eutectic melt). The projection of the K2CO3–CaCO3–MgCO3 liquidus surface is divided into the eight primary crystallization fields for magnesite, aragonite, dolomite, Ca-dolomite, K2Ca3(CO3)4, K8Ca3(CO3)7, K2Mg(CO3)2, and K2CO3. The temperature increase is accompanied by the sequential disappearance of crystalline phases in the following sequence: K8Ca3(CO3)7 (1220 °C) → K2Mg(CO3)2 (1250 °C) → K2Ca3(CO3)4 (1350 °C) → K2CO3 (1425 °C) → dolomite (1450 °C) → CaCO3 (1660 °C) → magnesite (1780 °C). The high Ca# of about 40 of the K2(Mg, Ca)(CO3)2 compound found as inclusions in diamond suggest (1) its formation and entrapment by diamond under the P–T conditions of 6 GPa and 1100 °C; (2) its remelting during transport by hot kimberlite magma, and (3) repeated crystallization in inclusion that retained mantle pressure during kimberlite magma emplacement. The obtained results indicate that the K–Ca–Mg carbonate melts containing 20–40 mol% K2CO3 is stable under P–T conditions of 6 GPa and 1100–1200 °C corresponding to the base of the continental lithospheric mantle. It must be emphasized that the high alkali content in the carbonate melt is a necessary condition for its existence under geothermal conditions of the continental lithosphere, otherwise, it will simply freeze.

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Section: Variety Of Carbonates In Diamonds and Their Originmentioning

confidence: 99%

The K2CO3–CaCO3–MgCO3 System at 6 GPa: Implications for Diamond Forming Carbonatitic Melts

et al. 2019

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“…Since the peak conditions estimated for the rocks from the Bohemian Massif 21 are significantly above 2 CP and the wet solidus for pelites, but close to the phengite decomposition and the miscibility gap for carbonatitic and silicate melt 37 , 44 , 45 , mechanisms 2 and 3 are better applicable to Bohemian rocks, where diamonds form during P–T increase. By contrast, on the retrograde path, decrease of P and T supresses carbon solubility, allowing attainment of saturation and triggering crystallization of diamond 42 . This mechanism can explain microdiamond occurrence inside fluid or melt inclusions in most UHP metamorphic terranes.…”

Section: Introductionmentioning

confidence: 99%

“…Solid-state transformation of graphite into diamond requires high activation energy and significant overstepping of the diamond-graphite transition curve or the presence of catalysts in amounts not available in natural systems 41 . However, in the presence of a fluid or melt, such conversion can happen at pressures close to the diamond-graphite transition curve 42 through simultaneous graphite dissolution and diamond precipitation driven by the difference in graphite and diamond solubility. Such a process of graphite to diamond transformation requires a constant source of excess carbon and a presence of melt or fluid.…”

Section: Introductionmentioning

confidence: 99%

Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature

Kotková

Fedortchouk

Wirth

et al. 2021

Sci Rep

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Metamorphic diamonds hosted by major and accessory phases in ultrahigh-pressure (UHP) metamorphic terranes represent important indicators of deep subduction and exhumation of continental crust at convergent plate boundaries. However, their nucleation and growth mechanisms are not well understood due to their small size and diversity. The Bohemian microdiamond samples represent a unique occurrence of monocrystalline octahedral and polycrystalline cubo-octahedral microdiamonds in two different metasedimentary rock types. By combining new and published data on microdiamonds (morphology, resorption, associated phases, carbon isotope composition) with P–T constraints from their host rocks, we demonstrate that the peak P–T conditions for the diamond-bearing UHP rocks cluster along water activity-related phase transitions that determine the microdiamond features. With increasing temperature, the diamond-forming medium changes from aqueous fluid to hydrous melt, and diamond morphology evolves from cubo-octahedral to octahedral. The latter is restricted to the UHP-UHT rocks exceeding 1100 °C, which is above the incongruent melting of phengite, where microdiamonds nucleate along a prograde P–T path in silicate-carbonate hydrous melt. The observed effect of temperature on diamond morphology supports experimental data on diamond growth and can be used for examining growth conditions of cratonic diamonds from kimberlites, which are dominated by octahedra and their resorbed forms.

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“…Under ƒO 2 conditions where pure carbonatite melt would be unstable, metasomatic melts may have a mixed carbonate-silicate character 19 . Spontaneous diamond crystallization through reduction of such a melt was recently demonstrated experimentally by Girnis et al 20 in a model peridotite-sediment system. Whether or not such processes are generally responsible for diamond formation in the Earth's mantle remains open to debate.…”

mentioning

confidence: 77%

Reduced methane-bearing fluids as a source for diamond

Matjuschkin

Woodland

Frost

et al. 2020

Sci Rep

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Diamond formation in the Earth has been extensively discussed in recent years on the basis of geochemical analysis of natural materials, high-pressure experimental studies, or theoretical aspects. Here, we demonstrate experimentally for the first time, the spontaneous crystallization of diamond from CH 4-rich fluids at pressure, temperature and redox conditions approximating those of the deeper parts of the cratonic lithospheric mantle (5-7 GPa) without using diamond seed crystals or carbides. In these experiments the fluid phase is nearly pure methane, even though the oxygen fugacity was significantly above metal saturation. We propose several previously unidentified mechanisms that may promote diamond formation under such conditions and which may also have implications for the origin of sublithospheric diamonds. These include the hydroxylation of silicate minerals like olivine and pyroxene, H 2 incorporation into these phases and the "etching" of graphite by H 2 and cH 4 and reprecipitation as diamond. This study also serves as a demonstration of our new high-pressure experimental technique for obtaining reduced fluids, which is not only relevant for diamond synthesis, but also for investigating the metasomatic origins of diamond in the upper mantle, which has further implications for the deep carbon cycle.

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Graphite to diamond transformation during sediment–peridotite interaction at 7.5 and 10.5 GPa

Cited by 8 publications

References 50 publications

The K2CO3–CaCO3–MgCO3 System at 6 GPa: Implications for Diamond Forming Carbonatitic Melts

The K2CO3–CaCO3–MgCO3 System at 6 GPa: Implications for Diamond Forming Carbonatitic Melts

Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature

Reduced methane-bearing fluids as a source for diamond

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Graphite to diamond transformation during sediment–peridotite interaction at 7.5 and 10.5 GPa

Cited by 8 publications

References 50 publications

The K2CO3–CaCO3–MgCO3 System at 6 GPa: Implications for Diamond Forming Carbonatitic Melts

The K2CO3–CaCO3–MgCO3 System at 6 GPa: Implications for Diamond Forming Carbonatitic Melts

Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature

Reduced methane-bearing fluids as a source for diamond

Contact Info

Product

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About

Graphite to diamond transformation during sediment–peridotite interaction at 7.5 and 10.5 GPa