Diamond genesis, mantle fractionations and mantle nitrogen content: a study of δ13C–N concentrations in diamonds

Cartigny, Pierre; Harris, Jeff W.; Javoy, M.

doi:10.1016/s0012-821x(00)00357-5

Cited by 193 publications

(133 citation statements)

References 49 publications

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“…It is logical that the residual carbonate is enriched with 13 C. Thus, experimental data showed that nitrogen-poor diamonds grew in the reduced 13 C-depleted part of capsule, whereas nitrogen-rich diamonds occurred in the oxidized 13 C-enriched part of capsule. This general tendency of a simultaneous decrease of 13 C value and N abundance in diamonds fits well the "limit sector" correlation of N abundance and 13 C values in natural diamonds worldwide (57). One of the possible reasons of such observed interrelations of nitrogen and 13 C concentrations in natural diamonds can be a segregation of carbonate melt to form a diaper and its subsequent migration (38,58) that can lead to the formation of contrasting domains of carbon isotopes in the Earth's low mantle.…”

Section: Significancesupporting

confidence: 82%

Mantle–slab interaction and redox mechanism of diamond formation

Palyanov

Bataleva

Sokol

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

176

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Subduction tectonics imposes an important role in the evolution of the interior of the Earth and its global carbon cycle; however, the mechanism of the mantle-slab interaction remains unclear. Here, we demonstrate the results of high-pressure redox-gradient experiments on the interactions between Mg-Ca-carbonate and metallic iron, modeling the processes at the mantle-slab boundary; thereby, we present mechanisms of diamond formation both ahead of and behind the redox front. It is determined that, at oxidized conditions, a low-temperature Ca-rich carbonate melt is generated. This melt acts as both the carbon source and crystallization medium for diamond, whereas at reduced conditions, diamond crystallizes only from the Fe-C melt. The redox mechanism revealed in this study is used to explain the contrasting heterogeneity of natural diamonds, as seen in the composition of inclusions, carbon isotopic composition, and nitrogen impurity content.carbonate-iron interaction | high-pressure experiment | mantle mineralogy | deep carbon cycle S ubduction of crustal material plays an important role in the global carbon cycle (1-6). Depending on oxygen fugacity and pressure-temperature (P-T) conditions, carbon exists in the Earth's interior in the form of carbides, diamond, graphite, hydrocarbons, carbonates, and CO 2 (7-11). In the upper mantle, the oxygen fugacity (fO 2 ) varies from one to five log units below the fayalitemagnetite-quartz (FMQ) buffer, with a trend of a decrease with depth (6,(12)(13)(14)(15). At a depth of ∼250 km, mantle is reported to become metal saturated (16, 17), which holds true for all mantle regions below, including the transition zone and lower mantle. The subduction of the oxidized crustal material occurs to depths greater than 600 km (4-6). The main carbon-bearing minerals of the subducted materials are carbonates, which are thermodynamically stable up to P-T conditions of the lower mantle (10,11,18). As evidenced by the compositions of inclusions in diamond, which vary from strongly reduced, e.g., metallic iron and carbides (19-23), to oxidized, e.g., carbonates and CO 2 (6,20,(24)(25)(26)(27)(28), carbonates may be involved in the reactions with reduced deep-seated rocks, including Fe 0 -bearing species (29-31). A scale of these reactions is determined mainly by the capacity of subducted carbonate-bearing domains. An important consequence of such an interaction is that it can produce diamond. However, studies on diamond synthesis via the reactions between oxidized and reduced phases are limited (32-35).To understand the mechanisms of the interaction of carbonbearing oxidized-and reduced-mineral assemblages, we performed high-pressure experiments with an iron-carbonate system; an approach was used that enabled the creation of an oxygen fugacity gradient in the capsules (Materials and Methods and SI Materials and Methods). Results and DiscussionThe experimental results and the phase compositions are given in Table 1 and Table S1, respectively. At temperatures of 1,000 and 1,100°C, the iron-car...

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Section: Significancesupporting

confidence: 82%

Mantle–slab interaction and redox mechanism of diamond formation

Palyanov

Bataleva

Sokol

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

176

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“…There is a growing body of data documenting coupled variation of nitrogen concentration and carbon isotope fractionation during diamond growth [26][27][28][29][30]. It has been suggested that nitrogen behavior is influenced by both diamond growth rate [31] and f O 2 [22].…”

Section: Fractionation Of Nitrogenmentioning

confidence: 99%

“…It has been suggested that nitrogen behavior is influenced by both diamond growth rate [31] and f O 2 [22]. According to "a limit sector" model [26], nitrogen must be generally incompatible in diamond at kinetic fractionation, since nitrogen content in diamonds suggested going lower with lowering diamond growth rate. Stachel et al [27] argued that, in case of equilibrium fractionation, nitrogen can be moderately compatible (K N = 2) in diamond under reduced conditions and strongly compatible (K N = 4), when diamond formed from an oxidized fluid.…”

Section: Fractionation Of Nitrogenmentioning

confidence: 99%

Experimental and Theoretical Evidence for Surface-Induced Carbon and Nitrogen Fractionation during Diamond Crystallization at High Temperatures and High Pressures

et al. 2017

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Isotopic and trace element variations within single diamond crystals are widely known from both natural stones and synthetic crystals. A number of processes can produce variations in carbon isotope composition and nitrogen abundance in the course of diamond crystallization. Here, we present evidence of carbon and nitrogen fractionation related to the growing surfaces of a diamond. We document that difference in the carbon isotope composition between cubic and octahedral growth sectors is solvent-dependent and varies from 0.7 in a carbonate system to 0.4 in a metal-carbon system. Ab initio calculations suggest up to 4 instantaneous 13 C depletion of cubic faces in comparison to octahedral faces when grown simultaneously. Cubic growth sectors always have lower nitrogen abundance in comparison to octahedral sectors within synthetic diamond crystals in both carbonate and metal-carbon systems. The stability of any particular growth faces of a diamond crystal depends upon the degree of carbon association in the solution. Octahedron is the dominant form in a high-associated solution while the cube is the dominant form in a low-associated solution. Fine-scale data from natural crystals potentially can provide information on the form of carbon, which was present in the growth media.

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“…Open-system processes are perhaps more realistic reflections of natural processes and provide the potential for much larger isotopic fractionations to occur. Smart et al (2011) considered two situations where Rayleigh-type fractionation may cause large isotopic fractionation during diamond formation by using numerical modelling: (1) fractionation during direct diamond precipitation from a fluid/melt and (2) fractionation related to the source fluid/melt prior to diamond formation (model of Cartigny et al 2001). They concluded in both scenarios that only minute quantities of isotopically light carbon could be produced if fractionating from mantle material.…”

Section: Subducted Source Of Isotopically Light Carbonmentioning

confidence: 99%

Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions

Thomson

Kohn²,

Bulanova

et al. 2014

Contrib Mineral Petrol

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interpreted as evidence of diamond growth from abiotic organic carbon added to the oceanic crust during hydrothermal alteration. The bulk isotopic composition of the oceanic crust, carbonates plus organics, is equal to the composition of mantle carbon (−5 ‰), and we suggest that recycling/mixing of subducted material will replenish this reservoir over geological time. Several exposed, syngenetic inclusions have bulk compositions consistent with former eclogitic magnesium silicate perovskite, calcium silicate perovskite and NAL or CF phases that have reequilibrated during their exhumation to the surface. There are multiple occurrences of majoritic garnet with pyroxene exsolution, coesite with and without kyanite exsolution, clinopyroxene, Fe or Fe-carbide and sulphide minerals alongside single occurrences of olivine and ferropericlase. As a group, the inclusions have eclogitic affinity and provide evidence for diamond formation at pressures extending to Earth's deep transition zone and possibly the lower mantle. It is observed that the major element composition of inclusions and isotopic compositions of host Juina-5 diamonds are not correlated. The diamond and inclusion compositions are intimately related to subducted material and record a polybaric growth history across a depth interval stretching from the lower mantle to the base of the lithosphere. It is suggested that the interaction of slabderived melts and mantle material combined with subsequent upward transport in channelised networks or a buoyant diapir explains the formation of Juina-5 diamonds. We conclude that these samples, despite originating at great mantle depths, do not provide direct information about the ambient mantle, instead, providing a snapshot of the Earth's deep carbon cycle. Keywords Diamonds · Sub-lithospheric mantle · Carbon cycle · SubductionAbstract Forty-one diamonds sourced from the Juina-5 kimberlite pipe in Southern Brazil, which contain optically identifiable inclusions, have been studied using an integrated approach. The diamonds contain <20 ppm nitrogen (N) that is fully aggregated as B centres. Internal structures in several diamonds revealed using cathodoluminescence (CL) are unlike those normally observed in lithospheric samples. The majority of the diamonds are composed of isotopically light carbon, and the collection has a unimodal distribution heavily skewed towards δ 13 C ~ −25 ‰. Individual diamonds can display large carbon isotope heterogeneity of up to ~15 ‰ and predominantly have isotopically lighter cores displaying blue CL, and heavier rims with green CL. The light carbon isotopic compositions are Communicated by O. Müntener. Electronic supplementary materialThe online version of this article

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Diamond genesis, mantle fractionations and mantle nitrogen content: a study of δ13C–N concentrations in diamonds

Cited by 193 publications

References 49 publications

Mantle–slab interaction and redox mechanism of diamond formation

Mantle–slab interaction and redox mechanism of diamond formation

Experimental and Theoretical Evidence for Surface-Induced Carbon and Nitrogen Fractionation during Diamond Crystallization at High Temperatures and High Pressures

Origin of sub-lithospheric diamonds from the Juina-5 kimberlite (Brazil): constraints from carbon isotopes and inclusion compositions

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