Plate Flexure Control on Melt Transport in the Oceanic Lithosphere: Implications for Petit-Spot Volcanism

Petit-spots are volcanoes with relatively small volumes of magma production found on the seafloor of subducting plates (Hirano et al., 2006, Harmon et al., 2025). Geochemical observations suggest petit-spots are derived from low-degree asthenospheric melts with a crustal and/or carbonatitic component (Mikuni et al., 2024), while others suggest additional interaction with metasomatic zones during migration (Buchs et al., 2013). Their occurrence near the outer-rise region, where plate bending generates extension at the base of the lithosphere and compression at the top, suggests creation of fast melt pathways through otherwise cold, thick lithosphere (Hirano et al., 2006). However, the extent to which flexure-induced stresses influence melt migration, especially in a lithosphere with strong rheological contrasts, remains poorly quantified. 

Here, we use numerical models of melt transport across the brittle–ductile transition (Li et al., 2023, 2025, Pusok et al., 2025) to investigate how plate flexure influences melt transport that facilitates petit-spot volcanism. Flexure is introduced in our models through prescribed boundary loading, producing depth-dependent compression and extension separated by a neutral surface. We systematically test how the magnitude of bending, the position of the neutral surface, hydraulic and rheological parameters influence the style of melt transport, melt focusing and melt ascent efficiency. We demonstrate that extensional stresses at the base of the lithosphere can localise melt into efficient ascent pathways that traverse the overlying compressional domain. Conversely, strong rheological contrasts near the brittle–ductile transition can divert melt laterally and accumulate melt at interfaces, limiting flux to the surface despite extension at the base of the lithosphere. This work provides a quantitative basis for understanding when flexure promotes upward melt transport versus trapping melt at rheological interfaces within the oceanic lithosphere.

 

References 

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Harmon et al. (2025). Evidence for petit-spot volcanism in the Puerto Rico Trench. GRL 52, doi:10.1029/2024GL114362.

Hirano et al. (2006) Volcanism in response to plate flexure. Science 313, doi:10.1126/science.1128235.

Li et al. (2023), Continuum approximation of dyking with a theory for poro-viscoelastic–viscoplastic deformation, GJI, doi:10.1093/gji/ggad173.

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