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Abstract
We analyse results of dredge sampling, a high‐resolution seismic reflection survey, and unpublished petroleum industry data from part of the overriding continental plate of the Fiordland subduction zone. Plate tectonic calculations show that convergence rates have progressively increased since Miocene time, when subduction‐related processes started. An initial deformation phase was characterised by reverse throw on pre‐existing structures during the interval 16–8 Ma. This is interpreted to be when a throughgoing subduction interface developed, as fracture zone linkage and spreading ridge extinction occurred south of New Zealand. A Pliocene‐Quaternary deformation phase characterised by renewed folding and reverse faulting on structures subparallel to the plate boundary may be due to a regional change in plate motion or the inherited geometry of the Eocene continent/ocean transition that is obliquely colliding with the plate boundary, or both. Initial uplift of the region south of Fiordland to sea level was followed by c. 1800 m of subsidence at the Snares Depression. This subsidence may have been an isostatic response to tectonic erosion of a crustal root, or due to negative slab buoyancy associated with greater total convergence, or both. Persistence of Fiordland topographic elevations above sea level, and continued rock uplift of Fiordland, is likely to be related to greater initial crustal thickness of the overriding Pacific plate in the north, and the present southward transition from continental collision to intra‐oceanic subduction. The locations of the first three subduction‐related volcanoes have a relationship to pre‐existing faults and raise the possibility that volcanism and deformation may be intimately associated during subduction initiation.