The Hikurangi Plateau is an

oceanic plateau An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the ...

in the South Pacific Ocean east of the

North Island The North Island, also officially named Te Ika-a-Māui, is one of the two main islands of New Zealand, separated from the larger but much less populous South Island by the Cook Strait. The island's area is , making it the world's 14th-larges ...

of New Zealand. It is part of a

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...

(LIP) together with Manihiki and Ontong Java, now located and north of Hikurangi respectively. Mount Hikurangi, in

Māori mythology Māori mythology and Māori traditions are two major categories into which the remote oral history of New Zealand's Māori may be divided. Māori myths concern fantastic tales relating to the origins of what was the observable world for the pr ...

the first part of the North Island to emerge from the ocean, gave its name to the plateau.

Geological setting

The Hikurangi Plateau covers approximately and reaches below sea level. Hikurangi Plateau is cut by the Hikurangi Channel, a 2000 km abyssal channel that starts at Kaikoura and runs along the

Hikurangi Trench The Hikurangi Trench, also called the Hikurangi Trough, is an oceanic trench in the bed of the Pacific Ocean off the east coast of the North Island of New Zealand, lying between the southern end of the Cook Strait and the Chatham Rise. It is t ...

as far as the

Māhia Peninsula Māhia Peninsula (Maori: or ) is located on the east coast of New Zealand's North Island, in the Hawke's Bay region, between the towns of Wairoa and Gisborne. Rocket Lab has set up its Launch Complex 1 close to Ahuriri Point at the south ...

before crossing the plateau and ending in the South-west Pacific abyssal plain.

Tectonic evolution

Two models have been proposed for the formation of Hikurangi. It can be derived from the mantle plume that caused the break-up of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final sta ...

and the separation of

Zealandia Zealandia (pronounced ), also known as (Māori) or Tasmantis, is an almost entirely submerged mass of continental crust that subsided after breaking away from Gondwanaland 83–79 million years ago.Gurnis, M., Hall, C.E., and Lavier, L.L., ...

from Antarctica 107 Ma. Alternatively, it could have formed together with other Pacific plateaux around 120 Ma as part of the Ontong Java- Manihiki-Hikurangi mega-plateau, in which case Hikurangi must have drifted thousands of kilometres during the Cretaceous silent period (84–121 Ma) before colliding with Gondwana. A 2010 study of isotopic data supported the mega-plateau or " Greater Ontong Java Event" model. The study added several basins as remains of this LIP event, including the north-west part of the Central Pacific, Nauru, East Mariana, and Lyra basins — submarine volcanism that must have covered 1% of Earth's surface and had a dramatic impact on life on Earth. There are, nevertheless, traces in seamounts on Hikurangi of a second Late Cretaceous magmatic event contemporaneous with volcanism on New Zealand and associated with the final break-up of Gondwana. The Hikurangi Plateau has been partly subducted under the

Chatham Rise The Chatham Rise is an area of ocean floor to the east of New Zealand, forming part of the Zealandia continent. It stretches for some from near the South Island in the west, to the Chatham Islands in the east. It is New Zealand's most productiv ...

, probably during the Cretaceous, and probably resulting in a slab more than long. The western margin of the plateau is actively subducting under the

of New Zealand to a depth of . With these missing portions of the plateau added to it, the Hikurangi Plateau originally must have covered , an area similar to that of the Manihiki Plateau to the north. The Hikurangi Plateau first subducted beneath New Zealand around 100 Ma during the Gondwana collision and it is currently subducting a second time as part of the convergence between the Pacific and Australian plates. These subducted parts are reaching into the mantle beneath the North Island and northern

South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...

. The extent of the Hikurangi Plateau slab suggests that it has played a significant role in the

geology of New Zealand The geology of New Zealand is noted for its volcanic activity, earthquakes and geothermal areas because of its position on the boundary of the Australian Plate and Pacific Plates. New Zealand is part of Zealandia, a microcontinent nearly half t ...

during the past 100 Ma. The

Southern Alps The Southern Alps (; officially Southern Alps / Kā Tiritiri o te Moana) is a mountain range extending along much of the length of New Zealand's South Island, reaching its greatest elevations near the range's western side. The name "Southern ...

in central South Island are being uplifted along the plate boundary there, a fault zone which parallels the western edge of the slab of the Hikurangi Plateau. The Australian and Pacific plates converge obliquely in the Tonga-Kermadec-Hikurangi subduction zone. The Hikurangi Plateau alters this subduction beneath North Island, at the Hikurangi subduction zone, where the buoyancy of the slab has resulted in the exposure of a

forearc Forearc is a plate tectonic term referring to a region between an oceanic trench, also known as a subduction zone, and the associated volcanic arc. Forearc regions are present along a convergent margins and eponymously form 'in front of' the v ...

and hence earthquakes such as the 7.8 M_w 1931 Hawke's Bay earthquake.

References

Notes

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* * * * {{Oceanic features of Zealandia, state=collapsed Geography of the New Zealand seabed Plateaus of the Pacific Ocean Large igneous provinces

Geological setting

Tectonic evolution

See also

References

Notes

Sources