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When Silicates Protect Abiotic Organic Carbon All the Way to the Mantle
During the transformation of oceanic lithosphere rocks through a process known as serpentinization, solid organic compounds can form abiotically. This study shows that these compounds can be preserved in certain rocks called metaserpentinites, even when they are carried deep into the Earth under mantle conditions.
This contrasts with organic matter of biological origin found in other rocks, which is typically transformed into graphite and isotopically altered during burial.
In metaserpentinites, these organic compounds retain a disordered structure and characteristic chemical elements, notably nitrogen. They also display very light isotopic signatures, reflecting their specific origin. This preservation is made possible by their encapsulation within a dense mineral matrix, which limits exchanges with surrounding fluids.
These results suggest that such rocks could transport organic carbon deep into the Earth more efficiently than previously thought. They may help explain certain chemical signatures observed in deeply formed diamonds, and highlight the need to better integrate this process into our overall understanding of the carbon and nitrogen cycles within the Earth.
In metaserpentinites, these organic compounds retain a disordered structure and characteristic chemical elements, notably nitrogen. They also display very light isotopic signatures, reflecting their specific origin. This preservation is made possible by their encapsulation within a dense mineral matrix, which limits exchanges with surrounding fluids.
These results suggest that such rocks could transport organic carbon deep into the Earth more efficiently than previously thought. They may help explain certain chemical signatures observed in deeply formed diamonds, and highlight the need to better integrate this process into our overall understanding of the carbon and nitrogen cycles within the Earth.
Figure : Characterization of solid organic compounds in Alpine eclogitic metaserpentinites.
(a–b) SEM-SE (secondary electrons) and SEM-BSE (backscattered electrons) images of carbonaceous material trapped within chlorite and antigorite layers. Raman spectra of the solid organic compounds are characterized by broad disordered bands and graphite bands (DCM : disordered carbonaceous material).
(c) Examples of raw FTIR spectra of antigorite (black) and carbonaceous material associated with antigorite (red).
The full study is published in : Nature communications
References :
Debret, B., Bouilhol, P., Bouquerel, H. et al. (2026) Organic carbon recycling in subduction zones. Nature Communications. doi:10.1038/s41467-026-71559-
Scientific contacts :
- Stéphane Schwartz - Associate Professor at Université Grenoble Alpes, Institute of Earth Sciences (ISTerre), Grenoble, France