Nitrogen isotope systematics and origins of mixed-habit diamonds

Howell, D.; Stern, Richard A.; Griffin, William L.; Southworth, RE; Mikhail, Sami; Stachel, Thomas

doi:10.1016/j.gca.2015.01.033

Cited by 15 publications

(12 citation statements)

References 63 publications

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“…The results from our ab initio calculations provide strong support for 12 C isotope affinity to cubic growth diamond relative to octahedral crystal faces. The difference of 3.75 is expected within the first crystal layer at 1400 K (Figure 2).…”

Section: Ab Initio Calculations Of Carbon Isotope Fractionationmentioning

confidence: 55%

“…In the first layer, the instantaneous difference in δ 13 C between cube and octahedra is expected to be 3.75‰ at 1400 K, and this decreases to 1.85‰ at 2000 K. This difference disappears completely once one models seven or more layers below the crystal surface. Octahedron and rhombododecahedron surfaces display complicated relationships with a changeover in the affinity of 12 C isotope arising at the fifth layer inside the crystal lattice ( Figure 2). However, a clear qualitative difference of certain isotope affinity between faces of cubes and of octahedra can be traced at least down to the fifth layer.…”

Section: Ab Initio Calculations Of Carbon Isotope Fractionationmentioning

confidence: 99%

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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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Section: Ab Initio Calculations Of Carbon Isotope Fractionationmentioning

confidence: 55%

Section: Ab Initio Calculations Of Carbon Isotope Fractionationmentioning

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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“…Howell et al (2015) also noted minor fractionation between octahedral and cuboid growth sectors, but in the three "star" diamonds that they studied, they found no difference in the carbon isotopes and an average difference of 0.4-1‰ in δ 15 N (with maximum differences between contemporaneous spots reaching 2‰). However, in this case the octahedral sector is richer in 15 N. Howell et al (2015) also observed large differences in [N] between the two sectors. In the samples they studied, both sectors are rich in nitrogen but the octahedral sector (average ~2700 ppm) carries higher concentrations than the cuboid sector (~2000 ppm).…”

Section: Discussionmentioning

confidence: 93%

“…In both sectors, the isotope ratios increase during the growth of the diamond, but spots sampling contemporaneous growth in the two sectors are separated by about 1.2‰. Howell et al (2015) also noted minor fractionation between octahedral and cuboid growth sectors, but in the three "star" diamonds that they studied, they found no difference in the carbon isotopes and an average difference of 0.4-1‰ in δ 15 N (with maximum differences between contemporaneous spots reaching 2‰). However, in this case the octahedral sector is richer in 15 N. Howell et al (2015) also observed large differences in [N] between the two sectors.…”

Section: Discussionmentioning

confidence: 93%

Carbon and nitrogen systematics in nitrogen-rich, ultradeep diamonds from Sao Luiz, Brazil

et al. 2018

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Three diamonds from Sao Luiz, Brazil carrying nano-and micro-inclusions of molecular δ-N2 that exsolved at the base of the transition zone were studied for their carbon and nitrogen isotopic composition and the concentration of nitrogen utilizing SIMS. The diamonds are individually uniform in their carbon isotopic composition and most spot analyses yield δ 13 C values of-3.2±0.1‰ (ON-SLZ-390) and-4.7±0.1‰ (ON-SLZ-391 and 392). Only a few analyses deviate from these tight ranges and all fall within the main mantle range of-5±3‰. Most of the nitrogen isotope analyses also have typical mantle δ 15 N values (-6.6±0.4‰,-3.6±0.5‰ and-4.1±0.6‰ for ON-SLZ-390, 391 and 392, respectively) and are associated with high nitrogen concentrations of 800-1250 atomic ppm. However, some nitrogen isotopic ratios, associated with low nitrogen concentrations (<400 ppm) and narrow Manuscript Click here to download Manuscript Navon et al Carbon and nitrogen systematics in TZ diamonds.docx zones with bright luminescence are distinctly above the average, reaching positive  15 N values. These sharp fluctuations can neither be attributed to fractionation nor are they easily explained by introduction of new pulses of melt or fluid. We discuss the possibility that they result from fractionation between different growth directions, so that distinct  15 N values and nitrogen concentrations may form during diamond growth from a single melt/fluid. Other more continuous variations, in the core of ON-SLZ-390 or the rim of ON-SLZ-392 may be the result of Rayleigh fractionation or mixing.

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“…The most common method applied to constrain nitrogen uptake into diamond is reverse modeling of empirical data. This method assigns a fluid-diamond partition coefficient for nitrogen by fitting the co-variations of carbon-isotope values and nitrogen abundances to a curve for a given temperature (using theoretical equilibrium carbon-isotope fractionation factors that assume the speciation of carbon as methane or carbonate: Javoy et al, 1984;Boyd et al, 1987Boyd et al, , 1992Boyd and Pillinger, 1994;Bulanova et al, 2002Bulanova et al, , 2014Cartigny et al, 1997Cartigny et al, , 1998aCartigny et al, ,b, 2001Cartigny et al, , 2003Cartigny et al, , 2004Cartigny et al, , 2009Klein-BenDavid et al, 2010;Harte et al, 1999;Hauri et al, 2002;Howell et al, 2013Howell et al, , 2015aGautheron et al, 2005;Hutchison et al, 1997;Mikhail et al, 2013Mikhail et al, , 2014aStachel and Harris, 2009;Palot et al, 2009Palot et al, , 2012Palot et al, , 2014Thomassot et al, 2007Thomassot et al, , 2009, where T is independently determined using the degree of nitrogen aggregation and/or geothermometry on paired silicate inclusions (discussed by Stachel and Harris, 2008).…”

Section: Introductionmentioning

confidence: 99%

A petrological assessment of diamond as a recorder of the mantle nitrogen cycle

Mikhail¹,

Howell²

2016

American Mineralogist

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Nitrogen is fundamental to the evolution of Earth and the life it supports, but for reasons poorly understood, it is cosmochemically the most depleted of the volatile elements. The largest reservoir in the bulk silicate Earth is the mantle, and knowledge of its nitrogen geochemistry is biased, because ≥90% of the mantle nitrogen database comes from diamonds. However, it is not clear to what extent diamonds record the nitrogen characteristics of the fluids/melts from which they precipitate. There is ongoing debate regarding the fundamental concept of nitrogen compatibility in diamond, and empirical global datasets reveal trends indicative of nitrogen being both compatible (fibrous diamonds) and incompatible (non-fibrous monocrystalline diamonds). A more significant and widely overlooked aspect of this assessment is that nitrogen is initially incorporated into the diamond lattice as single nitrogen atoms. However, this form of nitrogen is highly unstable in the mantle, where nitrogen occurs as molecular forms like N2, or NH4 + , both of which are incompatible in the diamond lattice. A review of the available data shows that in classic terms, nitrogen is the most common substitutional impurity found in natural diamonds because it is of very similar atomic size and charge to carbon. However, the speciation of nitrogen, and how these different species disassociate during diamond formation to create transient monatomic nitrogen, are the factors governing nitrogen abundance in diamonds. This suggests the counter-intuitive notion that a nitrogen-free (Type II) diamond could grow from a N-rich media that is simply not undergoing reactions that liberate monatomic N. In contrast, a nitrogen-bearing (Type I) diamond could grow from a fluid with a lower N abundance, in which reactions are occurring to generate (unstable) N atoms during diamond formation. This implies that diamond's relevance to nitrogen abundance in the mantle is far more complicated than currently

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Nitrogen isotope systematics and origins of mixed-habit diamonds

Cited by 15 publications

References 63 publications

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

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

Carbon and nitrogen systematics in nitrogen-rich, ultradeep diamonds from Sao Luiz, Brazil

A petrological assessment of diamond as a recorder of the mantle nitrogen cycle

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