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Updated: Nov 9, 2025
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Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction
Published on: April 1, 2017
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Metamorphic microdiamond formation is controlled by water activity, phase transitions and temperature
J Kotková1,2, Y Fedortchouk3, R Wirth4
1Czech Geological Survey, Klárov 3, 118 21, Prague 1, Czech Republic. jana.kotkova@geology.cz.
Scientific Reports
|April 9, 2021
Summary
Metamorphic microdiamonds reveal insights into deep subduction processes. Their morphology, from cubo-octahedral to octahedral, indicates changes in the diamond-forming medium from aqueous fluid to hydrous melt with increasing temperature.
Area of Science:
- Geology
- Mineralogy
- Petrology
Background:
- Metamorphic diamonds in ultrahigh-pressure (UHP) terranes are key indicators of deep crustal subduction and exhumation.
- Understanding their nucleation and growth is challenging due to small size and diversity.
Purpose of the Study:
- To investigate the nucleation and growth mechanisms of microdiamonds from the Bohemian UHP metamorphic terrane.
- To correlate microdiamond features with peak pressure-temperature (P-T) conditions and fluid evolution.
Main Methods:
- Analysis of microdiamond morphology, resorption, and associated phases.
- Determination of carbon isotope composition.
- Integration with P-T constraints from host metasedimentary rocks.
Main Results:
- Microdiamond features are linked to water activity-related phase transitions at peak P-T conditions.
- Diamond morphology evolves from cubo-octahedral to octahedral with increasing temperature (aqueous fluid to hydrous melt).
- Octahedral diamonds form above 1100 °C in silicate-carbonate hydrous melt along a prograde path.
Conclusions:
- Temperature significantly influences microdiamond morphology and growth environment.
- Findings support experimental data on diamond growth and aid in understanding cratonic diamond formation.
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