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A study of the link between subduction initiation and platform subsidence in New Zealand revealed that flexural foredeep was not responsible for the observed 1500 meter subsidence due to a broad wavelength, which was greater than 200 kilometers. Viscous mantle flow models predict that platform subsidence, which occurs above subduction zones, may cause depression that are two kilometers deep and 500 to 1000 kilometers wide.

Abstract: 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. [ABSTRACT FROM AUTHOR]

Wide-angle reflection and refraction data recorded during the Seismic Array HiKurangi Experiment (SAHKE) are used to constrain the crustal P-wave velocity (Vp) structure along two profiles spanning the length and width of Wanganui Basin, located landwards of the southern Hikurangi subduction margin, New Zealand. These models provide high-resolution constraints on the structure and crustal thickness of the overlying Australian and subducted Pacific plates and plate interface geometry. Wide-angle reflections are modelled to show that the subducted oceanic Pacific plate crust is anomalously thick (~10 km) below southern North Island and is overlain by a ~1.5-4.0 km thick, low Vp (4.8-5.4 km s-1) layer, interpreted as a channel of sedimentary material, that persists landwards at least as far as Kapiti Island. Distinct near vertical reflections from onshore shots identify a ~4 km high mound of low-velocity sedimentary material that appears to underplate the overlying Australian plate crust and is likely to contribute to local rock uplift along the Axial ranges. The overriding Australian plate Moho beneath Wanganui Basin is imaged as deepening southwards and reaches a depth of at least 36.4 km. The Moho shape approximately mirrors the thickening of the basin sediments, suggestive of crustal downwarping. However, the observed crustal thickness variation is insufficient to explain the large negative Bouguer gravity anomaly (-160 mGal) centred over the basin. Partial serpentinization within the upper mantle with a concomitant density decrease is one possible way of reconciling this anomaly. [ABSTRACT FROM AUTHOR]