Zealandia

Zealandia (/ziːˈlændiə/), also known as Te Riu-a-Māui (Māori)[2] or Tasmantis,[3] is an almost entirely submerged mass of continental crust that subsided after breaking away from Gondwanaland 83–79 million years ago.[4] It has variously been described as a continental fragment, a microcontinent, a submerged continent, and a continent.[5] The name and concept for Zealandia was proposed by Bruce Luyendyk in 1995.[6]

Not to be confused with Zeelandia.
For other uses, see Zealandia (disambiguation).

Topography of Zealandia. The linear ridges running north-northeast (Colville to the west and Kermadec to the east, separated by the Havre Trough and Lau Basin) and southwest (the Resolution Ridge System) away from New Zealand are not considered part of the continental fragment, nor are Australia (upper left), Vanuatu or Fiji (top centre).[1]

The landmass may have been completely submerged by about 23 million years ago,[7][8] and most of it (93%) remains submerged beneath the Pacific Ocean.[9] New Zealand is the largest part of Zealandia that is above sea level, followed by New Caledonia. With a total area of 4,920,000 km2 (1,900,000 sq mi), it is the world's largest current microcontinent, more than twice the size of the next-largest microcontinent and more than half the size of the Australian continent. As such, and due to other geological considerations, such as crustal thickness and density, it is arguably a continent in its own right.[10] This was the argument which made news in 2017,[11] when geologists from New Zealand, New Caledonia, and Australia concluded that Zealandia fulfills all the requirements to be considered a continent, rather than a microcontinent or continental fragment.[5] New Zealand geologist Nick Mortimer has commented that "if it wasn't for the ocean, it would have been recognized as such long ago".[12]

Zealandia supports substantial inshore fisheries and contains gas fields, of which the largest known is New Zealand's Maui gas field, near Taranaki. Permits for oil exploration in the Great South Basin were issued in 2007.[13] Offshore mineral resources include iron sands, volcanic massive sulfides and ferromanganese nodule deposits.[14]

Geology
See also: Geology of New Zealand and Geography of New Caledonia
Topographic map of Zealandia
Most of Zealandia is underwater. Ball's Pyramid, near Lord Howe Island, is one place where it rises above sea level

Zealandia is largely made up of two nearly parallel ridges, separated by a failed rift, where the rift breakup of the continent stops and becomes a filled graben. The ridges rise above the sea floor to heights of 1,000–1,500 m (3,300–4,900 ft), with few rocky islands rising above sea level. The ridges are continental rock, but are lower in elevation than normal continents because their crust is thinner than usual, approximately 20 km (12 mi) thick, and consequently they do not float as high above Earth's mantle.

About 25 million years ago, the southern part of Zealandia (on the Pacific Plate) began to shift relative to the northern part (on the Indo-Australian Plate). The resulting displacement by approximately 500 km (310 mi) along the Alpine Fault is evident in geological maps.[15] Movement along this plate boundary has also offset the New Caledonia Basin from its previous continuation through the Bounty Trough.

Compression across the boundary has uplifted the Southern Alps, although due to rapid erosion their height reflects only a small fraction of the uplift. Farther north, subduction of the Pacific Plate has led to extensive volcanism, including the Coromandel and Taupo Volcanic Zones. Associated rifting and subsidence has produced the Hauraki Graben and more recently the Whakatane Graben and Wanganui Basin.

Volcanism on Zealandia has also taken place repeatedly in various parts of the continental fragment before, during and after it rifted away from the supercontinent Gondwana. Although Zealandia has shifted approximately 6,000 km (3,700 mi) to the northwest with respect to the underlying mantle from the time when it rifted from Antarctica, recurring intracontinental volcanism exhibits magma composition similar to that of volcanoes in previously adjacent parts of Antarctica and Australia.

This volcanism is widespread across Zealandia but generally of low volume apart from the huge mid to late Miocene shield volcanoes that developed the Banks and Otago Peninsulas. In addition, it took place continually in numerous limited regions all through the Late Cretaceous and the Cenozoic. However, its causes are still in dispute. During the Miocene, the northern section of Zealandia (Lord Howe Rise) might have slid over a stationary hotspot, forming the Lord Howe Seamount Chain.

Zealandia is occasionally divided by scientists into two regions, North Zealandia (or Western Province) and South Zealandia (or Eastern Province), the latter of which contains most of the Median Batholith crust. These two features are separated by the Alpine Fault and Kermadec Trench and by the wedge-shaped Hikurangi Plateau, and are moving separately to each other.[10]

Classification as a continent

The case for Zealandia being a continent in its own right was argued by Nick Mortimer and Hamish Campbell in their book Zealandia: Our continent revealed in 2014,[10] citing geological and ecological evidence to support the proposal.[16]

In 2017, a team of eleven geologists from New Zealand, New Caledonia, and Australia concluded that Zealandia fulfils all the requirements to be considered a drowned continent, rather than a microcontinent or continental fragment.[5] This verdict was widely covered by news media.[17][18][19]

Biogeography

New Caledonia lies at the northern end of the ancient continent, while New Zealand rises at the plate boundary that bisects it. These land masses are two outposts of the Antarctic Flora, including Araucarias and Podocarps. At Curio Bay, logs of a fossilized forest closely related to modern Kauri and Norfolk pine can be seen that grew on Zealandia about 180 million years ago during the Jurassic period, before it split from Gondwana.[20] These were buried by volcanic mud flows and gradually replaced by silica to produce the fossils now exposed by the sea.

During glacial periods, more of Zealandia becomes a terrestrial rather than a marine environment. Zealandia was originally thought to have no native land mammal fauna, but the discovery in 2006 of a fossil mammal jaw from the Miocene in the Otago region shows otherwise.[21]

Political divisions
Exclusive economic zone of New Zealand and continental shelf boundaries for much of Zealandia

The total land area (including inland water bodies) of Zealandia is 286,655 km2 (110,678 sq mi). Of this, New Zealand comprises the majority, at 267,988 km2 (103,471 sq mi, or 93%) which includes the mainland (the North and South Islands), nearby islands, and most outlying islands, including the Chatham Islands, the New Zealand Subantarctic Islands, the Solander Islands, and the Three Kings Islands (but not the Kermadec Islands or Macquarie Island (Australia), which are part of the rift).

New Caledonia and the islands surrounding it comprise some 18,576 km2 (7,172 sq mi or 7%) and the remainder is made up of various territories of Australia including the Lord Howe Island Group (New South Wales) at 56 km2 (22 sq mi or 0.02%), Norfolk Island at 35 km2 (14 sq mi or 0.01%), as well as the Elizabeth and Middleton Reefs (Coral Sea Islands Territory) with 0.25 km2 (0.097 sq mi).

Population

The total human population of Zealandia today is about 5 million people.

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See also

References
  1. "Figure 8.1: New Zealand in relation to the Indo-Australian and Pacific Plates". The State of New Zealand’s Environment 1997. 1997. Retrieved 20 April 2007.
  2. "The origin and meaning of the name Te Riu-a-Māui/Zealandia". www.gns.cri.nz. GNS Science. 2 May 2019. Retrieved 11 August 2020.
  3. Danver, Steven L. (22 December 2010). Popular Controversies in World History: Investigating History's Intriguing Questions. ABC-CLIO. p. 187. ISBN 978-1-59884-078-0. Archived from the original on 5 August 2016. Zealandia or Tasmantis, with its 3.5 million square km territory being larger than Greenland, ...
  4. Gurnis, M., Hall, C.E., and Lavier, L.L., 2004, Evolving force balance during incipient subduction: Geochemistry, Geophysics, Geosystems, v. 5, Q07001, https://doi.org/10.01029/02003GC000681
  5. Mortimer, Nick; Campbell, Hamish J. (2017). "Zealandia: Earth's Hidden Continent". GSA Today. 27. doi:10.1130/GSATG321A.1. Archived from the original on 17 February 2017.
  6. Luyendyk, Bruce P. (April 1995). "Hypothesis for Cretaceous rifting of east Gondwana caused by subducted slab capture". Geology. 23 (4): 373–376. doi:10.1130/0091-7613(1995)023<0373:HFCROE>2.3.CO;2.
  7. "Searching for the lost continent of Zealandia". The Dominion Post. 29 September 2007. Retrieved 9 October 2007. We cannot categorically say that there has always been land here. The geological evidence at present is too weak, so we are logically forced to consider the possibility that the whole of Zealandia may have sunk.
  8. Campbell, Hamish; Gerard Hutching (2007). In Search of Ancient New Zealand. North Shore, New Zealand: Penguin Books. pp. 166–167. ISBN 978-0-14-302088-2.
  9. Wood, Ray; Stagpoole, Vaughan; Wright, Ian; Davy, Bryan; Barnes, Phil (2003). New Zealand's Continental Shelf and UNCLOS Article 76 (PDF). Institute of Geological and Nuclear Sciences Limited. Institute of Geological and Nuclear Sciences series 56. Wellington, New Zealand: National Institute of Water and Atmospheric Research. p. 16. NIWA technical report 123. Archived from the original (PDF) on 21 February 2007. Retrieved 22 February 2007. The continuous rifted basement structure, thickness of the crust, and lack of seafloor spreading anomalies are evidence of prolongation of the New Zealand land mass to Gilbert Seamount.
  10. Mortimer, Nick; Campbell, Hamish (2014). Zealandia: Our continent revealed. North Shore, New Zealand: Penguin Books. pp. 72 ff. ISBN 978-0-14-357156-8.
  11. "Zealandia: Is there an eighth continent under New Zealand?". BBC News. 17 February 2017. Archived from the original on 28 March 2017. Retrieved 26 March 2017.
  12. "Zealandia continent".
  13. "Great South Basin – Questions and Answers". 11 July 2007. Archived from the original on 14 October 2008. Retrieved 18 April 2008.
  14. "New survey published on NZ mineral deposits". 30 May 2007. Archived from the original on 16 October 2008. Retrieved 18 April 2008.
  15. "Figure 4. Basement rocks of New Zealand". UNCLOS Article 76: The Land mass, continental shelf, and deep ocean floor: Accretion and suturing. Archived from the original on 27 September 2007. Retrieved 21 April 2007.
  16. Yarwood, V. (November–December 2014). "Zealandia: Our continent revealed". New Zealand Geographic. Book Review. Archived from the original on 29 July 2017. Retrieved 30 July 2017.
  17. Potter, Randall (16 February 2017). "Meet Zealandia: Earth's latest continent". CNN. Archived from the original on 17 February 2017.
  18. Hunt, Elle (16 February 2017). "Zealandia – pieces finally falling together for continent we didn't know we had". The Guardian. Archived from the original on 26 February 2017.
  19. East, Michael (16 February 2017). "Scientists discover 'Zealandia' – a hidden continent off the coast of Australia". The Telegraph. Archived from the original on 18 February 2017.
  20. "Fossil forest: Features of Curio Bay/Porpoise Bay". Archived from the original on 17 October 2008. Retrieved 6 November 2007.
  21. Campbell, Hamish; Gerard Hutching (2007). In Search of Ancient New Zealand. North Shore, New Zealand: Penguin Books. pp. 183–184. ISBN 978-0-14-302088-2.
  22. "Population clock as at Sunday, 08 Oct 2017 at 11:48:07 a.m." 8 October 2017. Archived from the original on 12 July 2017. Retrieved 7 October 2017.
  23. "268 767 habitants en 2014". ISEE. Archived from the original on 13 November 2014. Retrieved 16 November 2014.
  24. "Norfolk Island". The World Factbook. CIA. Archived from the original on 3 July 2015. Retrieved 22 July 2015.
  25. Australian Bureau of Statistics (27 June 2017). "Lord Howe Island (State Suburb)". 2016 Census QuickStats.
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