We postulate that the tholeiitic suite of the ophiolite represents the crustal segment of SSZ lithosphere (SSZL) generated in the southern South Fiji Basin (SFB) at a northeast-dipping subduction zone that was initiated at about 35 Ma. The subduction zone nucleated along a pre-existing transform boundary separating circa 45–20 Ma oceanic lithosphere to the north and west of the Northland Peninsula from nascent back arc basin lithosphere of the SFB. Construction of the SSZL propagated southward along the transform boundary as the SFB continued to unzip to the southeast. After subduction of a large portion of oceanic lithosphere by about 26 Ma and collision of the SSZL with New Zealand, compression between the Australian Plate and the Pacific Plate was taken up along a new southwest-dipping subduction zone behind the SSZL. Renewed volcanism began in the oceanic forearc at 25 Ma producing boninitic-like, SSZ and within-plate alkalic and calc-alkaline rocks. Rocks of these types temporally overlap ophiolite emplacement and subsequent Miocene continental arc construction.