Skip to content

Research at St Andrews

Evidence for multiple diamondite-forming events in the mantle

Research output: Contribution to journalArticle

DOI

Author(s)

Sami Mikhail, Frances McCubbin, Daniel Howell

School/Research organisations

Abstract

A collection of 35 diamondite samples (polycrystalline diamond aggregates, sometimes referred to as framesites), assumed to be from southern Africa, have been studied to investigate their infrared (IR) spectroscopic characteristics. Due to the abundance of sub-micrometer, interlocking diamonds (polycrystalline) with mineral and fluid inclusions within the diamond material affecting their transparency, only fragments from 10 of the samples provided high-quality data. The IR spectra showed a wide range of generally high-nitrogen concentrations (386–2677 ppm), with a full range of nitrogen aggregation states, from pure IaA to pure IaB. Platelet characteristics were interpreted as being regular (i.e., not having been affected by deformation and/or heating events), meaning the nitrogen aggregation data could be interpreted with confidence. Surprisingly, the platelet data showed a positive correlation between their intensity (integrated area) and peak position. The primary hydrogen band (at 3107 cm−1) and secondary band (at 1405 cm−1) are both often present in the samples’ spectra, but show no correlation with any other characteristic. There is also no correlation between the samples’ paragenesis (as defined by their garnet chemistry) and any of the IR characteristics. While we have no independent determination of the samples mantle residence age, nor the temperature they resided at, we infer that diamondite formation has occurred episodically over a large time frame in single and distinct growth events (as opposed to over a short time frame but over a large depth/temperature range). This idea is more in keeping with the theory that C-O-H diamond- (and diamondite-) forming fluids are the result of localized small volume processes. Interestingly, one sample contained fluid inclusions that exhibited a water:carbonate molar ratio (~0.8), similar to the saline and silicic end-members of the monocrystalline diamond-forming fluid chemical spectrum.
Close

Details

Original languageEnglish
Pages (from-to)1537-1543
JournalAmerican Mineralogist
Volume99
DOIs
Publication statusPublished - 1 Sep 2014

Discover related content
Find related publications, people, projects and more using interactive charts.

View graph of relations

Related by author

  1. Plume-lithosphere interaction, and the formation of fibrous diamonds

    Broadley, M. B., Kagi, H., Burgess, R., Zedgenizov, D., Mikhail, S., Almayrac, M., Ragozin, A., Pomazansky, B. & Sumino, H., 1 Oct 2018, In : Geochemical Perspectives Letters. 8, p. 26-30 5 p.

    Research output: Contribution to journalArticle

  2. The relationship between mantle pH and the deep nitrogen cycle

    Mikhail, S., Barry, P. H. & Sverjensky, D. A., 15 Jul 2017, In : Geochimica et Cosmochimica Acta. 209, p. 149-160 12 p.

    Research output: Contribution to journalArticle

  3. The geobiological nitrogen cycle: from microbes to the mantle

    Zerkle, A. L. & Mikhail, S., May 2017, In : Geobiology. 15, 13, p. 343-352 10 p.

    Research output: Contribution to journalArticle

  4. Low surface gravitational acceleration of Mars results in a thick and weak lithosphere: implications for topography, volcanism, and hydrology

    Heap, M. J., Byrne, P. K. & Mikhail, S., 1 Jan 2017, In : Icarus. 281, p. 103-114 12 p.

    Research output: Contribution to journalArticle

Related by journal

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

    Mikhail, S. & Howell, D., 1 Apr 2016, In : American Mineralogist. 101, 4, p. 780-787

    Research output: Contribution to journalArticle

  2. Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0-1.2 GPa and 950-1000 °C

    McCubbin, F., Vander Kaaden, K., Tartèse, R., Boyce, J., Mikhail, S., Whitson, E., Bell, A., Anand, M., Franchi, I., Wang, J. & Hauri, E., 1 Oct 2015, In : American Mineralogist. 100, 8-9, p. 1790-1802

    Research output: Contribution to journalArticle

  3. Titanium in muscovite, biotite, and hornblende: Modeling, thermometry, and rutile activities of metapelites and amphibolites

    Chambers, J. & Kohn, M., 2012, In : American Mineralogist. 97, 4, p. 543–555

    Research output: Contribution to journalArticle

  4. Combined single-crystal X-ray and neutron powder diffraction structure analysis exemplified through full structure determinations of framework and layer beryllate minerals

    Armstrong, J. A., Friis, H., Lieb, A., Finch, A. A. & Weller, M. T., Apr 2010, In : American Mineralogist. 95, 4, p. 519-526 8 p.

    Research output: Contribution to journalArticle

ID: 232146053