Research ArticleGEOLOGY

Melting of sediments in the deep mantle produces saline fluid inclusions in diamonds

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Science Advances  29 May 2019:
Vol. 5, no. 5, eaau2620
DOI: 10.1126/sciadv.aau2620
  • Fig. 1 Backscattered electron images of experimental charges.

    Locations of images (A) to (D) from sediment-peridotite reaction experiments are schematically shown in capsule on the left. (A, C, and D) Reaction experiments at 5 GPa/1000°C with superimposed energy-dispersive x-ray maps of chlorine [green in (C) and (D)]. The sediment half of two-layer experiments recrystallized to garnet and clinopyroxene (Cpx), whereas orthopyroxene (Opx), magnesite (Mgs), and Na-K chlorides formed at the leading edge of the reaction zone against the peridotite. (B) Peridotite layer in the reaction experiment at 3 GPa/900°C contained phlogopite (Phl) behind the magnesite + orthopyroxene zone, and Na-K chlorides were absent. (E and F) Sediment melting experiment (no peridotite included) at 4 GPa/1000°C showing silicate melt (E) in equilibrium with garnet (Gt), coesite (Coe), and Mg calcite (Mg-Cc) shown in (F). Scale bars, 100 μm (A and B) and 20 μm (C to F).

  • Fig. 2 K/Na ratios of experimental chlorides and saline micro-inclusions in diamonds.

    Most saline micro-inclusions (orange diamonds) (2, 7, 30) have a K/Na ratio between 1:1 and 9:1, similar to the ratios found in the experimental Na-K chlorides of this study (gray diamonds). Full analyses of chlorides are given in tables S9 to S12.

  • Fig. 3 Pressure-temperature stability of Na-K chlorides.

    Na-K chlorides are restricted to reaction experiments at 4 to 6 GPa, while at 3 and 4 GPa/1100°C, K is sequestered in phlogopite. When mobile, highly saline fluids (blue) rise to lower pressures along the cratonic geotherm, they stall and react to form phlogopite-bearing metasomes (brown). The depth of phlogopite crystallization coincides with the mid-lithospheric discontinuity (32).

  • Fig. 4 Ternary diagram of experimental phase compositions compared to diamond inclusions.

    Composition of saline and silicic diamond micro-inclusions (orange diamonds) (2, 7, 9, 30) and omphacite mineral inclusions in diamonds (red circles) (2) compared to clinopyroxenes (light gray diamonds), orthopyroxenes (pink triangles), olivines (green diamonds), magnesite (olive diamonds), and Na-K chlorides (gray triangles) from this study. The “carbonated peridotite” field represents various mixtures of Mg carbonate (magnesite) and silicates. Saline micro-inclusions are mixtures between the Na-K chloride and carbonated peridotite (green arrow). The source for protokimberlitic melts of Udachnaya-East (black squares) (40) is enriched in Na and K relative to carbonated peridotite and trends toward bulk kimberlite composition (pink stars) (44) by assimilating pyroxenes, as indicated by the pink arrow.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/5/eaau2620/DC1

    Fig. S1. Modal proportions of phases in the reaction experiments and the melting experiment.

    Fig. S2. K/Na and Cl/F in mica, melt, fluid, and solid halide phases (chlorides + fluorides).

    Fig. S3. Chloride map of 5 GPa/1000°C experiment.

    Fig. S4. Backscattered electron image of the 6 GPa/1100°C experiment showing an unpolished capsule half.

    Fig. S5. Composition of silicate phases in reaction experiments.

    Table S1. Phase relations of experiments.

    Table S2. Starting materials.

    Table S3. Reaction experiment (3 GPa/800°C).

    Table S4. Reaction experiment (3 GPa/850°C).

    Table S5. Reaction experiment (3 GPa/900°C).

    Table S6. Reaction experiment (3 GPa/1000°C).

    Table S7. Reaction experiment (4 GPa/900°C).

    Table S8. Sediment melting (4 GPa/1000°C).

    Table S9. Reaction experiment (4 GPa/1000°C).

    Table S10. Reaction experiment (4 GPa/1100°C).

    Table S11. Reaction experiment (5 GPa/1000°C).

    Table S12. Reaction experiment (6 GPa/1100°C).

    Table S13. Mass balance of 3 GPa/800°C reaction experiment.

    Table S14. Mass balance of 3 GPa/850°C reaction experiment.

    Table S15. Mass balance of 3 GPa/1000°C reaction experiment.

    Table S16. Mass balance of 4 GPa/1100°C reaction experiment.

    Table S17. Mass balance of 4 GPa/1000°C sediment melting experiment.

    Table S18. Mass balance of 5 GPa/1000°C reaction experiment.

    Reference (45)

  • Supplementary Materials

    The PDF file includes:

    • Fig. S1. Modal proportions of phases in the reaction experiments and the melting experiment.
    • Fig. S2. K/Na and Cl/F in mica, melt, fluid, and solid halide phases (chlorides + fluorides).
    • Fig. S3. Chloride map of 5 GPa/1000°C experiment.
    • Fig. S4. Backscattered electron image of the 6 GPa/1100°C experiment showing an unpolished capsule half.
    • Fig. S5. Composition of silicate phases in reaction experiments.
    • Table S1. Phase relations of experiments.
    • Reference (45)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Table S2 (Microsoft Excel format). Starting materials.
    • Table S3 (Microsoft Excel format). Reaction experiment (3 GPa/800°C).
    • Table S4 (Microsoft Excel format). Reaction experiment (3 GPa/850°C).
    • Table S5 (Microsoft Excel format). Reaction experiment (3 GPa/900°C).
    • Table S6 (Microsoft Excel format). Reaction experiment (3 GPa/1000°C).
    • Table S7 (Microsoft Excel format). Reaction experiment (4 GPa/900°C).
    • Table S8 (Microsoft Excel format). Sediment melting (4 GPa/1000°C).
    • Table S9 (Microsoft Excel format). Reaction experiment (4 GPa/1000°C).
    • Table S10 (Microsoft Excel format). Reaction experiment (4 GPa/1100°C).
    • Table S11 (Microsoft Excel format). Reaction experiment (5 GPa/1000°C).
    • Table S12 (Microsoft Excel format). Reaction experiment (6 GPa/1100°C).
    • Table S13 (Microsoft Excel format). Mass balance of 3 GPa/800°C reaction experiment.
    • Table S14 (Microsoft Excel format). Mass balance of 3 GPa/850°C reaction experiment.
    • Table S15 (Microsoft Excel format). Mass balance of 3 GPa/1000°C reaction experiment.
    • Table S16 (Microsoft Excel format). Mass balance of 4 GPa/1100°C reaction experiment.
    • Table S17 (Microsoft Excel format). Mass balance of 4 GPa/1000°C sediment melting experiment.
    • Table S18 (Microsoft Excel format). Mass balance of 5 GPa/1000°C reaction experiment.

    Files in this Data Supplement:

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