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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. Reorientation 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.
Subduction of oceanic plateaux are events that have occurred infrequently in Earth's history. Although rare, these events are thought to considerably influence regional tectonics and global plate motions. In the mid‐Cretaceous the oceanic Hikurangi Plateau collided with the formerly active East Gondwana margin: An event which falls into the same of a sudden change from subduction to extensional processes, including graben formation, development rift basin development, and exhumation of metamorphic core complexes in the Zealandia continent as well as a global‐scale plate reorganization event. In this study, we use recently acquired seismic refraction and gravity data along one profile across the submarine Chatham Rise, which represent a former accretionary wedge of the East Gondwana subduction zone. We demonstrate that the southward extent of the subducted Hikurangi Plateau in the lower crust beneath the submarine Chatham Rise along our profile is only ~150. This is ~150 km less than the previously suggested extent. Furthermore, we interpret that a slice of the subducted Phoenix Plate remains attached to the southern edge of the Hikurangi Plateau. We suggest that cessation of subduction in response to the Hikurangi Plateau jamming as well as the rollback and detachment of the Phoenix Plate slab played an important role in the changing tectonic forces across Zealandia in mid‐Cretaceous. Moreover, we suggest that the subduction cessation along the Hikurangi Plateau segment led to the fragmentation of the Gondwana subduction zone and Phoenix Plate, which significantly influenced and potentially prolonged the global mid‐Cretaceous plate reorganization event.
Submarine landslides can be several orders of magnitude larger than their terrestrial counterparts (Korup et al., 2007), and can have devastating and widespread consequences. The submarine landslide itself could
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