Carbon isotope ratios and nitrogen abundances in relation to
                  cathodoluminescence characteristics for some diamonds from the Kaapvaal Province,
                  S. Africa

Harte, B.; Fitzsimons, I. C. W.; Harris, Jeff W.; Otter, M.L.

doi:10.1180/002646199548961

Cited by 101 publications

(56 citation statements)

References 43 publications

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“…The carbon isotopes of the studied diamonds from three localities in China are thus interpreted to reflect the isotopic signature of their mantle source. Between core areas and outer growth zones within individual diamond or among separate diamonds, there are no correlations between the intensity of cathode luminescence and carbon isotope ratios, in accordance with the results of previous studies [19,38,39].…”

Section: Growth Zones Of Diamonds and Their Relationship To Carbon Issupporting

confidence: 81%

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Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

Chen¹,

Zhili

Lu³

et al. 2012

Chin. Sci. Bull.

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The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes. In this paper, in-situ SIMS (Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton. It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton; the former has a range of 6.0‰ to 2.0‰ (relative to VPDB) with an average value of 3.0‰ in their core areas, which is consistent with global peridotitic diamonds; the diamonds from the Yangtze Craton, however, have a carbon isotopic range from 8.6‰ to 3.0‰ with an average value of 7.4‰ in their core areas, being more consistent with global eclogitic diamonds. The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied. There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth, while no correlation was observed between   13 C and internal inclusions. The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization, and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds. In addition, the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances, implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other, not yet understood factors. The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton.

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Section: Growth Zones Of Diamonds and Their Relationship To Carbon Issupporting

confidence: 81%

“…In-situ analyses with SIMS indicated that carbon isotopes in diamond depict complex growth zones. Moreover, complicated relations exist between carbon isotopes and nitrogen content as well as nitrogen isotopes in different occurrences [14][15][16][17][18][19][20][21][22].…”

mentioning

confidence: 99%

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

Chen¹,

Zhili

Lu³

et al. 2012

Chin. Sci. Bull.

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show abstract

“…Ion microprobe studies of diamonds show variations from <100 ppm to >1000 ppm in very narrow growth zones in lithospheric diamonds (e.g. Harte et al, 1999a). Likewise, ion microprobe studies on LM diamonds show that substantial smallscale variations can occur within single diamonds; Hutchison et al (1999) record a variation from 0.1 to 260 ppm.…”

Section: Diamond Characteristicsmentioning

confidence: 99%

Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones

Harte¹

2010

Mineral. mag.

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205

132

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Studies of the inclusions contained in natural diamonds have shown the occurrence of minerals which must have formed at depths below the lithosphere and which may be closely matched with the silicate mineral assemblages determined by high pressure and temperature experimental studies for depths of 300 to 800 km in the Earth's mantle. The inclusions come principally from two main depth zones:(1) the lower asthenosphere and upper transition zone; (2) the Upper Mantle/Lower Mantle (UM/LM) boundary region and the uppermost LM. The inclusions from zone 1 are very largely majoritic garnets (with or without clinopyroxene) which indicate bulk compositions of eclogitic/metabasic affinity. The minerals from zone 2 include Ca-Si and Mg-Si perovskites and ferropericlase and are dominantly of metaperidotitic bulk composition, but include some possible metabasite assemblages. In many of these natural assemblages, the tetragonal almandine pyrope phase occurs rather than the garnet found in experiments.As natural diamonds are believed to crystallize in fluids/melts, the hypothesis is developed that the restriction of diamonds and inclusions of particular compositions to the above two depth intervals is because they are controlled by loci of fluid/melt occurrence. Attention is focused on subduction zones because both suites of inclusions show some evidence of subducted protoliths. The lower zone (600À800 km) coincides with the region where dehydration may be expected for hydrous ringwoodite and dense hydrous Mg-silicates formed in subducted peridotites. The dehydration of lawsonite in subducted metabasites provides a particular location for melt formation and the inclusion of the shallower (~300 km) majoritic inclusions. For the deeper majoritic inclusions in the region of the upper transition zone, melt development may occur as a consequence of the hydrous wadsleyite-to-olivine transformation, and such melt may then interact with the upper crustal portion of a subducting slab. These suggestions offer an explanation of the depth restrictions and the compositional restrictions of the inclusions. The differences in d13 C values in the host diamonds for the two suites of inclusions may also be explained on this basis.KEYWORDS: majoritic garnet, Ca-Si perovskite, Mg-Si perovskite, hydrous wadsleyite, hydrous ringwoodite, dense hydrous Mg-silicates, dehydration reactions. Introduction and backgroundTHIS paper considers the provenance of mineral inclusions found in natural diamonds which appear to come from below the Earth's lithosphere. Attention will be focused on the inclusions which appear to come from ultrabasic and basic bulk rock compositions. Comparison of these inclusions with experimental data shows that they have selective distributions with respect to depth: with basic ones coming predominantly from a region in the lower asthenosphere and upper transition zone, and ultrabasic ones from a region spanning the base of the transition zone Revi ew (TZ) and the uppermost lower mantle. The hypothesis will be developed that this d...

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“…For the EIMF measurements, the "synAT" standard (a synthetic "A" diamond crystal, partial slice "T") was used [43]. The characteristics of this reference material are: 230.4 ppm N (wt) and δ 13 C PDB of −23.92 as determined by combustion analysis using a gas source mass spectrometer (analysed by S.R.…”

Section: Samples and Methodsmentioning

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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Carbon isotope ratios and nitrogen abundances in relation to cathodoluminescence characteristics for some diamonds from the Kaapvaal Province, S. Africa

Cited by 101 publications

References 43 publications

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

Diamond formation in the deep mantle: the record of mineral inclusions and their distribution in relation to mantle dehydration zones

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

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