Polycrystalline Diamonds from Kimberlites: Snapshots of Rapid and Episodic Diamond Formation in the Lithospheric Mantle

Jacob, Dorrit E.; Mikhail, Sami

doi:10.2138/rmg.2022.88.03

Cited by 9 publications

(4 citation statements)

References 111 publications

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“…This melt/rock interaction also results in the deposition of polycrystalline diamond aggregates, which are rocks consisting mostly of diamond, in which silicate minerals are merely interstitial accessory phases [ 84 ]. We propose that these may be a main reservoir of ‘redox frozen’ carbon in the lower lithosphere and particularly the TBL.…”

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

“…We propose that these may be a main reservoir of ‘redox frozen’ carbon in the lower lithosphere and particularly the TBL. The deposition reaction explains why the mineral suite of polycrystalline diamonds contrasts with most diamonds in being dominated by websteritic garnets (57% vs. 3% in peridotitic diamonds), whereas clinopyroxenes have compositions typical of peridotites and olivines are notably absent [ 84 ]. The carbon for the diamonds may be supplied by the reduced melts, in which carbon solubility is low but not insignificant [ 85 ], or from locally pre-existing carbonates.…”

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

“…(c) Reduced melts emanating from deeper in the asthenosphere (Fig. 6d ) never attain the oxidation state necessary to form carbonate, depositing diamonds as polycrystalline diamond aggregates associated with websteritic silicate minerals [ 84 , 86 ]. These may be easily remobilized when overprinted by carbonate melts as in (a) and (b).…”

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

“…An additional source of diamond in the lower cratonic lithosphere unrelated to subduction is melting deeper in the mantle in reduced environments (Figs 6b, d , 7c ). This may result in considerable diamond deposition for later reactivation, stored as polycrystalline diamonds: these are generally thought to be rare, but may represent up to 30% of diamond production at a single kimberlite pipe [ 84 ]. They are probably concentrated at the deepest lithospheric levels (Fig.…”

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

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The effects of local variations in conditions on carbon storage and release in the continental mantle

Foley,

Chen,

Jacob

2024

National Science Review

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Recent advances indicate that the amount of carbon released by gradual degassing from the mantle needs to be revised upwards, whereas the carbon supplied by plumes may have been overestimated in the past. Variations in rock types and oxidation state may be very local and exert strong influences on carbon storage and release mechanisms. Deep subduction may be prevented by diapirism in thick sedimentary packages, whereas carbonates in thinner sequences may be subducted. Carbonates stored in the mantle transition zone will melt when they heat up, recognised by coupled stable isotope systems (e.g. Mg, Zn, Ca). There is no single ‘mantle oxygen fugacity’, particularly in the thermal boundary layer (TBL) and lowermost lithosphere where very local mixtures of rock types coexist. Carbonate-rich melts from either subduction or melting of the uppermost asthenosphere trap carbon by redox freezing or as carbonate-rich dykes in this zone. Deeply-derived, reduced melts may form further diamond reservoirs, recognised as polycrystalline diamonds associated with websteritic silicate minerals. Carbon is released by either edge-driven convection, which tears sections of the TBL and lower lithosphere down so that they melt by a mixture of heating and oxidation, or by lateral advection of solids beneath rifts. Both mechanisms operate at steps in lithosphere thickness and result in carbonate-rich melts, explaining the spatial association of craton edges and carbonate-rich magmatism. High-pressure experiments on individual rock types, and increasingly on reactions between rocks and melts, are fine-tuning our understanding of processes and turning up unexpected results that are not seen in studies of single rocks. Future research should concentrate on elucidating local variations and integrating these with the interpretation of geophysical signals. Global concepts such as average sediment compositions and a uniform mantle oxidation state are not appropriate for small-scale processes; an increased focus on local variations will help to refine carbon budget models.

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Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

Section: Entrapment Of Carbon In the Continental Lithospherementioning

confidence: 99%

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The effects of local variations in conditions on carbon storage and release in the continental mantle

Foley,

Chen,

Jacob

2024

National Science Review

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Imperfections in natural diamond: the key to understanding diamond genesis and the mantle

Day,

Pamato,

Novella

et al. 2023

Riv. Nuovo Cim.

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Diamond has unique physical, thermal, electrical, and optical properties with respect to other minerals and related synthetic compounds that make it extremely valuable from an economic and industrial perspective. Natural diamond that forms in the upper mantle, transition zone, and lower mantle may encapsulate mantle minerals during growth and protect them from physical breakdown and chemical alteration upon ascent of the diamond to the surface via kimberlite eruption. Such mineral inclusions serve as the only direct means to study the deep Earth and provide critical information about the pressure, temperature, and redox conditions and the chemical and isotopic composition of the mantle. Natural diamonds show a wide range of ages and thus allow one to reconstruct the history of large-scale Earth processes, such as the formation and amalgamation of Earth’s lithosphere, the onset and evolution of tectonic processes (e.g., Wilson cycles), and the recycling of C, H, and N between different primordial and crustal reservoirs. In this review, a detailed description of all types of imperfections (e.g., mineral and fluid inclusions and structural defects) and the methods by which such imperfections can be analyzed to elucidate aspects of Earth’s complex geologic history is given.

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Origin of framesite revisited: Possible implications for the formation of CLIPPIR diamonds

Moore

Helmstaedt

2023

Earth-Science Reviews

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Polycrystalline Diamonds from Kimberlites: Snapshots of Rapid and Episodic Diamond Formation in the Lithospheric Mantle

Cited by 9 publications

References 111 publications

The effects of local variations in conditions on carbon storage and release in the continental mantle

The effects of local variations in conditions on carbon storage and release in the continental mantle

Imperfections in natural diamond: the key to understanding diamond genesis and the mantle

Origin of framesite revisited: Possible implications for the formation of CLIPPIR diamonds

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