Decoding metamorphic nanodiamonds formation through their internal structures

Sotelšek, Tim (author), Janák, Marian (author), Šturm, Sašo (author), Semsari Parapari, Sorour (author), Gračanin, Nik (author), Radan, Kristian (author), Gülgün, Mehmet Ali (author), Milovská, Stanislava (author), Vrabec, Mirijam (author)

Metamorphic diamonds offer insights into Earth's evolution, modulating the global carbon cycle through subduction into the mantle and exhumation. However, the formation and internal structure of minute diamonds remain poorly understood. Here, we study the internal structures of diamond-bearing inclusions from the Eastern Alps using state-of-the-art analytical techniques. Atomically resolved images revealed intricate structures, including well-faceted monocrystalline diamonds, complex nanocrystalline clusters of intergrown diamond and graphite and amorphous matter. Associated fluids contain CO$_2$, CH$_4$ and H$_2$O, indicating formation from C–O–H fluids. The proposed model of C–O–H fluid behaviour suggests monocrystalline diamond precipitation at the onset of retrograde metamorphism. Amorphous layers formed through interaction between the trapped fluid and the host garnet during the further exhumation. When the fluid reached the P–T conditions of the transition zone between the diamond and graphite stability fields, polycrystalline clusters formed. For the first time, we can see a detailed record of metamorphic fluids evolution, preserved in the internal structures of microsized diamond inclusions.

• Language: English
• Keywords: amorphous matter, C–O–H fluids, metamorphic diamonds, Raman spectroscopy, TEM
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: Str. 226–245
• Numbering: Vol. 44, iss. 3
• PID: 20.500.12556/RUL-180921
• UDC: 55
• ISSN on article: 0263-4929
• DOI: 10.1111/jmg.70032
• COBISS.SI-ID: 263396611
• Publication date in RUL: 19.03.2026

Record is a part of a journal

• Title: Journal of metamorphic geology
• Shortened title: J. metamorph. geol.
• Publisher: Wiley
• ISSN: 0263-4929
• COBISS.SI-ID: 735253

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.