Fluid Mobility and Element Recycling in Subduction Zones

Subduction zones are convergent plate boundaries where oceanic lithosphere descends into the mantle, triggering a cascade of metamorphic reactions that release aqueous fluids and melts. These fluids mobilise volatile elements (notably H₂O, C, S, halogens and boron) and trace metals from the subducting slab into the overlying mantle wedge. The liberated constituents induce mantle melting, drive arc volcanism and contribute to global geochemical cycles by returning recycled material to the surface. Fluid pathways are often channelised along shear zones or through dehydration reactions in serpentinites, amphiboles and other hydrous phases. The efficiency of element transfer depends on pressure–temperature conditions, slab composition and the interplay between fluid–rock reactions and melt percolation. A comprehensive understanding of fluid mobility and element recycling informs models of volcanic hazard, mantle heterogeneity, long-term climate regulation and the distribution of economically important metals.

Research from Nature Portfolio

Evidence from deep-mantle melt inclusions reveals that chlorine derived from seawater-altered oceanic crust survives subduction to form a substantial Cl-rich reservoir in the lower mantle. Radiogenic Pb isotopes linked to Cl-rich inclusions demonstrate ancient recycled crust contributions deep below. Analyses of Dominican Republic serpentinites show that during subduction and mineral transitions (lizardite to antigorite), fluorine and boron are largely retained, while chlorine, bromine and iodine are expelled. Forearc serpentinite compositions mirror arc magma halogen ratios, underlining the role of dehydrating serpentinite in generating volatiles for arc magmatism.

Fluid Mobility and Element Recycling in Subduction Zones publication trend

The graph below shows the total number of articles in fluid mobility and element recycling in subduction zones across all publications each year (not limited to Nature Index journals).

Technical terms

Subduction zone: A tectonic boundary where one lithospheric plate sinks beneath another into the mantle. Serpentinite: A rock rich in hydrated magnesium silicate minerals formed by seawater alteration of ultramafic mantle peridotite. Fluid-mobile elements: Chemical species (e.g. H₂O, halogens, boron) that preferentially partition into aqueous fluids or melts during metamorphic dehydration. Mantle wedge: The region of mantle above the subducting slab that undergoes metasomatism and melting due to slab-derived fluids. Melt inclusion: Tiny pockets of magma trapped within growing crystals that preserve the composition of original melts and volatiles. Channelised flow: Concentrated fluid pathways along fractures or shear zones facilitating rapid transport of fluids and elements. Hydrous phase: A mineral containing structurally bound water (e.g. amphibole, antigorite) that releases fluid upon breakdown. Dehydration reaction: A metamorphic process where hydrous minerals break down, liberating water and associated solutes. Volatile cycle: The global transfer of fluid constituents between Earth’s surface, crust and mantle over geological time.

References

1. On the role of Earth's lithospheric mantle in global volatile cycles. Earth and Planetary Science Letters (2023).
2. Tiny droplets of ocean island basalts unveil Earth’s deep chlorine cycle. Nature Communications (2019).
3. Tracing halogen and B cycling in subduction zones based on obducted, subducted and forearc serpentinites of the Dominican Republic. Scientific Reports (2017).
4. Slab-derived halogens and noble gases illuminate closed system processes controlling volatile element transport into the mantle wedge. Earth and Planetary Science Letters (2017).