Geochemical Processes in Eclogitic Mantle Dynamics

Eclogitic mantle dynamics concern the fate of oceanic crust that has been transformed under high‐pressure, high‐temperature conditions into dense metamorphic rock known as eclogite. During subduction, partial melting, fluid release and mineral reactions drive the mobilisation of major and trace elements, as well as isotopic species, reshaping the composition and redox state of the overlying mantle wedge. Recycled eclogite fragments carried by ascending magmas produce xenoliths and mineral inclusions in diamonds, offering windows into deep geochemical cycles. These processes influence the thermal evolution of cratonic lithosphere, control the speciation and transport of volatile components such as carbon and sulfur, and generate redox heterogeneities that affect mantle melting, metasomatism and ore deposition. By integrating petrological observations with in situ geochemical and isotopic measurements, researchers have begun to unravel the complex interplay between fluid–rock interactions, element partitioning and deep‐carbon storage in the convecting mantle.

Research from Nature Portfolio

Recent studies have shown that epitaxial relationships and inclusion morphology alone cannot reliably distinguish minerals that grew simultaneously with their diamond hosts from those that predated them. Re‐analysis of periclase and magnesiochromite inclusions demonstrates that most mineral inclusions act as nuclei for diamond rather than products of its growth, calling for a reassessment of diamond inclusion chronologies. In parallel, investigations of vanadium partitioning between garnet inclusions and host clinopyroxene have revealed that eclogitic diamond formation conserves oxygen in a closed‐system manner, buffering the oxygen fugacity of the lithospheric mantle over geological time. These findings refine our understanding of redox evolution, demonstrating that diamond encapsulation can preserve pristine snapshots of mantle conditions and that diamonds themselves can act as stabilising agents for deep‐mantle fO2.

Geochemical Processes in Eclogitic Mantle Dynamics publication trend

The graph below shows the total number of articles in geochemical processes in eclogitic mantle dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Eclogite: A high‐pressure metamorphic rock composed mainly of garnet and omphacitic clinopyroxene, derived from subducted oceanic crust.

Xenolith: A fragment of deep mantle or crustal rock entrained and brought to the surface by an ascending magma.

Oxygen fugacity (fO2): A measure of the chemical potential of oxygen in a system, controlling the redox state of minerals and melts.

Protogenetic: Describing a mineral inclusion that formed prior to the host rock or host mineral.

Syngenetic: Describing a mineral inclusion that formed simultaneously with and by the same process as its host rock or mineral.

References

1. A critique of using epitaxial criterion to discriminate between protogenetic and syngenetic mineral inclusions in diamond. Scientific Reports (2024).
2. Mineral inclusions in diamonds may be synchronous but not syngenetic. Nature Communications (2017).
3. Evidence for oxygen-conserving diamond formation in redox-buffered subducted oceanic crust sampled as eclogite. Nature Communications (2022).
4. Petrogenesis and Geodynamic Significance of Xenolithic Eclogites. Annual Review of Earth and Planetary Sciences (2023).
5. Mélange Signatures and Low Oxygen Fugacity in Eclogite Xenoliths From the Crust‐Mantle Transition Below a Mesoproterozoic Collision Belt. Journal of Geophysical Research: Solid Earth (2024).
6. Protogenetic clinopyroxene inclusions in diamond and Nd diffusion modeling—Implications for diamond dating. Geology (2022).