Newly forming subduction zones on Earth can provide insights
into the evolution of major fault zone geometries from shallow
levels to deep in the lithosphere and into the role of fluids in
element transport and in promoting rock failure by several
modes1,2. The transpressional subduction regime of New
Zealand, which is advancing laterally to the southwest below the
Marlborough strike–slip fault system of the northern South
Island3,4, is an ideal setting in which to investigate these processes.
Here we acquired a dense, high-quality transect of magnetotelluric
soundings across the system, yielding an electrical resistivity
cross-section to depths beyond 100 km. Our data imply three
distinct processes connecting fluid generation along the upper
mantle plate interface to rock deformation in the crust as the
subduction zone develops. Massive fluid release just inland of
the trench induces fault-fracture meshes through the crust above
that undoubtedly weaken it as regional shear initiates. Narrow
strike–slip faults in the shallow brittle regime of interior
Marlborough diffuse in width upon entering the deeper ductile
domain aided by fluids and do not project as narrow deformation
zones. Deep subduction-generated fluids rise from 100 km
or more and invade upper crustal seismogenic zones that have
exhibited historic great earthquakes on high-angle thrusts that
are poorly oriented for failure under dry conditions. The fluiddeformation
connections described in our work emphasize the
need to include metamorphic and fluid transport processes in
geodynamic models.
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