Fluids in Subduction Zone Processes

Fluids released from the descending oceanic plate drive many of the chemical and physical transformations at convergent margins. As hydrated minerals break down under increasing pressure and temperature, aqueous fluids rich in water, halogens and trace elements migrate into the overlying mantle wedge, promoting partial melting and arc magmatism. Under deep‐subduction conditions, fluids can attain supercritical states, greatly enhancing their capacity to transport silicate, carbon and sulphur species. These mobile phases induce metasomatism of the mantle, fertilise source regions for arc basalts and contribute to growth of continental crust. Fluid flow also influences seismic coupling, triggers intermediate‐depth earthquakes and governs mineral deposit formation. Laboratory experiments and high‐pressure observations reveal complex phase relations among aqueous fluids, saline solutions, melts and supercritical liquids. The resulting element cycling from slab to surface impacts global geochemical budgets and underpins resource formation in porphyry and epithermal systems. Advances in spectroscopic imaging, in situ trapping techniques and thermodynamic modelling have begun to resolve the composition, speciation and rheology of slab‐derived fluids across the subduction interface. By bridging petrology, geochemistry and geophysics, research on fluids in subduction zones illuminates fundamental processes in Earth’s deep carbon, water and element cycles, with implications for volcanic hazards, crustal evolution and mineral exploration.

Research from Nature Portfolio

Recent work has proposed that beyond the critical point in the mantle wedge, slab‐derived supercritical liquid separates into a hydrous felsic melt and an aqueous fluid. Field studies of arc volcanoes have revealed dacitic lavas consistent with direct eruption of this felsic melt, while the coexisting fluid phase induces basaltic magmas. This mechanism provides an efficient pathway for transferring silicate‐rich components from the subducting slab to the surface, offering a novel explanation for the generation of continental crust and the geochemical signatures of arc magmas.

Research from all publishers

High‐pressure studies of primary multiphase fluid inclusions in ultrahigh‐pressure metamorphic veins have directly characterised supercritical fluids deep in subduction zones. These inclusions preserve evidence for mobile carbon‐ and sulphur‐bearing phases, highlighting their role in global element cycling and in metamorphic carbon flux across the slab–mantle boundary.

A comprehensive review of aqueous fluid properties has shown that fluid composition, wettability and porosity control permeability and mass transport in the crust and mantle. It emphasises how dissolved halogens enhance solubility of key elements, how wetting angles govern channel formation, and how limited fluid fractions explain observed geophysical anomalies in mantle wedges above subducting slabs.

Thermodynamic modelling of complex H2O–CO2–NaCl–CaCl2 fluids relevant to deep petrogenesis has provided phase diagrams for multiphase behaviour up to 20 kbar and 1400 °C. This framework allows prediction of fluid densities, chemical activities and salt precipitation, offering insights into fluid evolution during slab dehydration and subsequent metasomatism of overlying mantle rocks.

Fluids in Subduction Zone Processes publication trend

The graph below shows the total number of articles in fluids in subduction zone processes across all publications each year (not limited to Nature Index journals).

Technical terms

Subduction zone: Region where one tectonic plate descends beneath another, creating high‐P–T conditions and releasing fluids.

Aqueous fluid: Water-rich liquid phase released during mineral dehydration, capable of dissolving and transporting elements.

Supercritical fluid: Phase beyond a substance’s critical point exhibiting properties intermediate between liquids and gases, with high solvating power.

Mantle wedge: Portion of the mantle above a subducting slab that is metasomatised and partially melted by slab‐derived fluids.

Fluid inclusion: Microscopic pocket of trapped fluid within a mineral that preserves composition and P–T history of geological fluids.

References

1. A new concept for the genesis of felsic magma: the separation of slab-derived supercritical liquid. Scientific Reports (2020).
2. Supercritical fluid in deep subduction zones as revealed by multiphase fluid inclusions in an ultrahigh-pressure metamorphic vein. Proceedings of the National Academy of Sciences of the United States of America (2023).
3. Fluids and physicochemical properties and processes in the Earth. Progress in Earth and Planetary Science (2022).
4. Thermodynamic Model of the Fluid System H2O–CO2–NaCl–CaCl2 at P-T Parameters of the Middle and Lower Crust. Petrology (2023).