Research ArticleGEOLOGY

The growth of lithospheric diamonds

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Science Advances  06 Jun 2018:
Vol. 4, no. 6, eaat1602
DOI: 10.1126/sciadv.aat1602
  • Fig. 1 Secondary electron mapping (SEM) images of a loose diamond extracted from the run products of sample H3908 by mechanical deposition on a stub covered with carbon tape before FIB preparation.

    (A) Diamond growth covers the whole initial seed. (B) Close-up of the surface exhibiting the formation and trapping of new spontaneously nucleated diamond crystals as inclusions. Scale bar, 2 μm.

  • Fig. 2 Sample H3908; upper left corner.

    (A) SEM image of a 5- to 8-μm-thick diamond seed plate containing inclusions resulting from FIB preparation. The plate was extracted with a micromanipulator and deposited on a silicon wafer previously placed in the sample chamber of the FIB. Red box, 30 μm × 30 μm; white box corresponding to inclusions, 25 μm2 area. (B) Close-up of a SE-SEM image of the area showing multiphased inclusions. Gray-level contrasts are density-dependent: dark gray, diamond (including diamond inclusions at the center of the image); medium gray, carbonates; and light gray, SiO2 (that is, coesite at 7 GPa). (C) Large NanoSIMS 12C map of the plate. (D) 12C mapping of the 25 μm2 area including the inclusions. “A” corresponds to diamond inclusions.

  • Fig. 3 Carbon isotopic compositions of both starting materials and newly synthesized diamonds.

    The starting materials are as follows: diamond seeds (gray triangles), graphite (dark triangle), and carbonate powders MELD and MELD + SIDERITE (white triangle); diamond samples are as follows: HBD01 (dark squares), H3913 (gray squares with black rims for the three fragments from map 2), and H3908 (white squares and white diamond are diamond inclusions). The areas delimited by dotted dark lines represent the two potential starting carbon sources: carbonates (MELD and MELD SID) and graphite. The gray triangles represent the composition of the starting diamond seeds. The isotopic composition of the bulk system (all carbon from graphite plus all carbon from carbonates) is calculated for each sample by mass balance and is presented as white circles: Bulk = xδ13Ccarbonate + yδ13Cgraphite, with x and y being initial mass proportions of carbonates and graphite, respectively. For this calculation, no fractionation coefficient is used because this is total mixing. The isotopic compositions of the samples range from the compositions of the starting seeds to those of the carbonate powders, reflecting mixing between the composition of the starting diamond seeds and the newly grown diamond areas. The diamond inclusions from sample H3908 exhibit a δ13C of −14.2‰, corresponding to a maximum fractionation Δ13C of −2.74‰ (within error bars) with the carbonate source MELD (carbonates).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaat1602/DC1

    table S1. Isotopic compositions of the starting materials, standards, and samples.

    table S2. Description of the studied samples.

    table S3. Mass balance calculations of isotopic compositions of the bulk composition for the starting materials and the high-pressure and high-temperature carbonate fluid.

    fig. S1. SEM images of the FIB preparation, cut on one side of the seed and on the other side to obtain the final slices.

    fig. S2. Details of the samples analyzed with the NanoSIMS.

    fig. S3. NanoSIMS maps of 12C for each investigated sample showing the locations of the areas of interest (red squares) corresponding to the location of the measurements reported in table S1 and Fig. 1.

    Reference (33)

  • Supplementary Materials

    This PDF file includes:

    • table S1. Isotopic compositions of the starting materials, standards, and samples.
    • table S2. Description of the studied samples.
    • table S3. Mass balance calculations of isotopic compositions of the bulk composition for the starting materials and the high-pressure and high-temperature carbonate fluid.
    • fig. S1. SEM images of the FIB preparation, cut on one side of the seed and on the other side to obtain the final slices.
    • fig. S2. Details of the samples analyzed with the NanoSIMS.
    • fig. S3. NanoSIMS maps of 12C for each investigated sample showing the locations of the areas of interest (red squares) corresponding to the location of the measurements reported in table S1 and Fig. 1.
    • Reference (33)

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