Geochemical Processes in Back-Arc Basin Magmatism

Back-arc basins develop where extensional regimes in the overriding plate of a subduction zone generate magmas that record the interplay between slab-derived inputs, mantle wedge dynamics and lithospheric architecture. Dehydration of the descending slab releases fluids and hydrous melts that metasomatise the overlying peridotitic mantle, lowering its solidus and promoting variable melting regimes. Resulting magmas range from tholeiitic basalts to boninitic and dacitic compositions, reflecting differences in pressure–temperature conditions, source heterogeneity and fractional crystallisation. Slab rollback drives corner flow that can replace enriched, metasomatised mantle with a more depleted peridotitic source, producing temporal shifts in slab-derived geochemical signatures. Trace-element distributions and radiogenic isotope systems (Sr–Nd–Pb–Hf) serve as powerful tracers of mantle source enrichment, slab-fluid contributions and crustal assimilation. Subsequent hydrothermal circulation along nascent oceanic crust further modifies mineralisation and influences the global cycles of key elements, underlining the importance of back-arc processes for reconstructing tectonic evolution, assessing volcanic hazards and guiding resource exploration.

Research from Nature Portfolio

Recent work in the New Hebrides back-arc shows that rapid slab steepening over the past 2.5 million years has driven swift replacement of an enriched, slab-metasomatised mantle wedge by more depleted peridotite, linking rollback dynamics to shifts in trace-element and isotopic compositions of erupted lavas. Isotopic studies in the northern Lau back-arc basin have also demonstrated selective ingress of a primordial mantle component (FOZO) sourced from the Samoan plume, with high-precision Hf–Nd–noble gas data revealing mixing between refractory mantle and a spatially restricted plume contribution, illuminating the complexity of plume–subduction interactions in back-arc magmatism.

Geochemical Processes in Back-Arc Basin Magmatism publication trend

The graph below shows the total number of articles in geochemical processes in back-arc basin magmatism across all publications each year (not limited to Nature Index journals).

Technical terms

Back-arc basin: an extensional region forming behind a volcanic arc in a subduction zone.

Mantle wedge: the zone of mantle between the downgoing slab and overlying lithosphere where melting occurs.

Slab rollback: the process by which the subducting plate steepens and retreats, inducing mantle flow.

Metasomatism: chemical alteration of mantle peridotite by fluid- or melt-mediated element transfer.

Boninite: a high-magnesium andesite formed by low-degree melting of a hydrous, depleted mantle source.

Tholeiitic basalt: a low-sodium basalt typical of mid-ocean ridges and back-arc spreading centres.

References

1. Slab steepening and rapid mantle wedge replacement during back-arc rifting in the New Hebrides. Nature Communications (2024).
2. Selective ingress of a Samoan plume component into the northern Lau backarc basin. Nature Communications (2015).
3. Geodynamic Evolution of the Lau Basin. Geophysical Research Letters (2024).
4. Effects of the Hydrous Domain in the Mantle Wedge on Magma Formation and Mixing at the Northeast Lau Spreading Center, SW Pacific. Geochemistry Geophysics Geosystems (2022).
5. Mantle source variations beneath the Eastern Lau Spreading Center and the nature of subduction components in the Lau basin–Tonga arc system. Geochemistry Geophysics Geosystems (2009).