Extent and Cessation of the Mid‐Cretaceous Hikurangi Plateau Underthrusting: Impact on Global Plate Tectonics and the Submarine Chatham Rise

Abstract

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.

A Forearc Stratigraphic Response to Cretaceous Plateau Collision and Slab Detachment, South Island, New Zealand

“…In contrast, Riefstahl et al. (2020) suggest that slab detachment from ∼90 Ma below the Chatham Rise is indicated by a 60° rotation in the direction of extension in the Bounty Trough (Figure 3a), and that tearing propagated eastwards from Marlborough after 100 Ma.…”

“…Resistance of the plateau to further subduction led to tearing and detachment of portions of the subducted slab, resulting in the emplacement of mildly alkaline volcanic rocks within the forearc (Hoernle et al., 2020; Tappenden, 2003). Seismic imaging indicates that oceanic crust remains contiguous with the Hikurangi Plateau below the North Island (Stern et al., 2015; Tozer et al., 2017), but has detached below the South Island (Riefstahl et al., 2020).…”

“…Hoernle et al (2020) proposed tearing below the north-eastern South Island from 99 Ma, based on the relative timing of volcanism, followed by tearing and westwards propagating slab detachment from the eastern edge of the Hikurangi Plateau from 86 Ma. In contrast, Riefstahl et al (2020) suggest that slab detachment from ∼90 Ma below the Chatham Rise is indicated by a 60° rotation in the direction of extension in the Bounty Trough (Figure 3a), and that tearing propagated eastwards from Marlborough after 100 Ma.…”

“…Evidence for ongoing subduction in Marlborough until 86 Ma aligns with accounts from the North Island and suggests these regions were not underplated by the Hikurangi plateau prior to this time (Cawood et al, 1999;Kamp, 1999Kamp, , 2000Mazengarb & Harris, 1994). We adopt the west to east detachment model of Riefstahl et al (2020), speculating that initial tearing of the Phoenix slab at 99 Ma occurred east of Marlborough and that plateau collision split the East Gondwana margin. Assuming a tear propagation speed of ∼300 km/Ma (Van Hunen & Allen, 2011), Riefstahl et al (2020) proposed initial detachment at 90 Ma, and that oceanic crust (slab) subsequently detached within 5 Ma below the Chatham Rise along a front ∼870 km wide.…”

“…We adopt the west to east detachment model of Riefstahl et al (2020), speculating that initial tearing of the Phoenix slab at 99 Ma occurred east of Marlborough and that plateau collision split the East Gondwana margin. Assuming a tear propagation speed of ∼300 km/Ma (Van Hunen & Allen, 2011), Riefstahl et al (2020) proposed initial detachment at 90 Ma, and that oceanic crust (slab) subsequently detached within 5 Ma below the Chatham Rise along a front ∼870 km wide. If initial tearing and detachment is instead assumed from 99 Ma until at least 90 Ma, based on forearc volcanism, the propagation speed was closer to 60 km/Ma, suggesting that tearing and detachment may have progressed irregularly.…”