The West Wishbone Ridge (WWR), east of New Zealand, has previously been interpreted as a Cretaceous plate boundary, although both the nature and timing of motion along this feature have been disputed. Here, using recently acquired seismic reflection data from the region of the intersection of the WWR with the Chatham Rise, we show that the WWR was primarily a dextral strike-slip fault during the Late Cretaceous. The WWR first propagated along the eastern margin of the Hikurangi Plateau after the collision of the Hikurangi Plateau with the Chatham Rise, in response to the slowing of spreading at the Osbourn Trough while spreading continued unabated east of the East Wishbone Ridge, from ca. 105 Ma. Reorienta-tion of spreading at the Osbourn Trough at this time resulted in short-lived, oblique subduction beneath the southern extent of the WWR. Motion along the WWR likely ceased with the cessation of Osbourn Trough spreading. Using our seismic reflection data and gravity modeling across those same profiles, we locate, for the first time, the eastern boundary of the Hikurangi Plateau between 42–43°S. We also find anomalously thick oceanic crust (~12 km thick) north of the Hikurangi Plateau. Matching tectonic fabric and fracture zone links between the East Wishbone Ridge and the De Gerlache Gravity Anomaly near Ellsworth Land on the West Antarctic margin indicates that these features were linked or parallel during the Late Cretaceous, and fed strike-slip motion southward into the Gondwana interior, contributing to the onset of Gondwana rifting ca. 85 Ma.