Map of the countries that make up ZealandiaTopography of Zealandia, outlined in pink. The linearridges running north-northeast (Colville to the west andKermadec to the east, separated by theHavre Trough andLau Basin) and southwest (the Resolution Ridge System) away from New Zealand are not considered part of Zealandia, nor areAustralia (left),Vanuatu, orFiji (top centre).[1]
By approximately 23 million years ago, the landmass may have been completely submerged.[11][12] Today, most of the landmass (94%) remains submerged beneath thePacific Ocean.[13]New Zealand is the largest part of Zealandia that is above sea level, followed byNew Caledonia.
Mapping of Zealandia concluded in 2023.[14] With a total area of approximately 4,900,000 km2 (1,900,000 sq mi),[6] Zealandia is substantially larger than any features termed microcontinents and continental fragments. If classified as a microcontinent, Zealandia would be the world's largest microcontinent. Its area is six times the area of the next-largest microcontinent,Madagascar,[6] and more than half the area of theAustralian continent. Zealandia is more than twice the size of the largest intraoceaniclarge igneous province (LIP) in the world, theOntong Java Plateau (approximately 1,900,000 km2 or 730,000 sq mi), and the world's largest island,Greenland (2,166,086 km2 or 836,330 sq mi). Zealandia is also substantially larger than theArabian Peninsula (3,237,500 km2 or 1,250,000 sq mi), the world's largestpeninsula, and theIndian subcontinent (4,300,000 km2 or 1,700,000 sq mi). Due to these and other geological considerations, such as crustal thickness and density,[15][16] some geologists from New Zealand, New Caledonia, and Australia have concluded that Zealandia fulfills all the requirements to be considered a continent rather than a microcontinent or continental fragment.[6] GeologistNick Mortimer commented that if it were not for the ocean level, it would have been recognised as such long ago.[17]
GNS Science recognises two names for the landmass. In English, the most common name isZealandia, a latinate name for New Zealand; the name was coined in the mid-1990s and became established through common use. In theMāori language, the landmass is namedTe Riu-a-Māui, meaning 'the hills, valleys, and plains ofMāui'.[2]
The Zealandia continent is largely made up of two nearly parallel ridges, separated by afailedrift, where the rift breakup of the continent stops and becomes a filledgraben. The ridges rise above thesea floor to heights of 1,000–1,500 m (3,300–4,900 ft), with a few rockyislands rising abovesea 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 so high above Earth'smantle as that of most landmasses.[citation needed]
About 25 million years ago, the southern part of Zealandia (on thePacific Plate) began to shift relative to the northern part (on theIndo-Australian Plate). The resulting displacement by approximately 500 km (310 mi) along theAlpine Fault is evident in geological maps.[20] Movement along this plate boundary also has offset theNew Caledonia Basin from its previous continuation through theBounty Trough.[citation needed]
Compression across the boundary has uplifted theSouthern 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 theCoromandel andTaupō Volcanic Zones. Associated rifting and subsidence has produced theHauraki Rift and more recently, theWhakatane Graben and Wanganui Basin.[citation needed]
Volcanism on Zealandia has taken place repeatedly in various parts of thecontinental fragment before, during, and after itrifted away from thesupercontinentGondwana. Although Zealandia has shifted approximately 6,000 km (3,700 mi) to the northwest with respect to the underlyingmantle from the time when it rifted fromAntarctica, recurring intracontinental volcanism exhibits magma composition similar to that of volcanoes in previously adjacent parts of Antarctica and Australia. Large volume magmatism occurred in two periods, being in theDevonian (370 to 368 million years ago) and the EarlyCretaceous (129 to 105 million years ago).[21]
This volcanism is widespread across Zealandia, but on present land generally it is of low volume apart from the huge mid to lateMioceneshield volcanoes that developed theBanks andOtago Peninsulas. In addition, it took place continually in numerous limited regions all through theLate Cretaceous and theCenozoic. Some of its causes remain in dispute perhaps because of data gaps.[21] During theMiocene, the northern section of Zealandia (Lord Howe Rise) might have slid over a stationaryhotspot, forming theLord Howe Seamount Chain.[22]
It has been suggested that Zealandia may have played an important part in the origin of the Pacific Ocean's volcanicRing of Fire.[23]
Occasionally, Zealandia is divided into two regions by scientists: North Zealandia (or Western Province); and South Zealandia (or Eastern Province), the latter of which contains most of the MedianBatholith crust. These two features are separated by theAlpine Fault andKermadec Trench and by the wedge-shapedHikurangi Plateau, and they are moving separately from each other.[15]
The case for Zealandia being a continent in its own right has been argued in the Nick Mortimer and Hamish Campbell bookZealandia: Our continent revealed (2014),[15] in which the authors presented geological and ecological evidence in support of their thesis.[24]
The younger Zealandia rocks have evidence of origins from earlyGondwana formations of 500 to 700 million years ago,Rodinia formations about a billion years ago and sources from anexpanded-Ur continent between 3.5 and 2 billion years ago.[28]
The breakup ofGondwana formed Northern Zealandia.[29] Zealandia underwent extension resulting from east to northeast-directed rollback of west to southwest-dipping subduction of thePacific Plate.[30] which terminated between 95 million[30] to 85 million years ago.[31] After 85 million years ago Zealandia separated from Australia through seafloor spreading of theCoral andTasman seas until this ceased 52 million years ago.[31] Shortening on an active convergent northern margin of Zealandia occurred mainly between 45 and 35 million years ago.[31] This was followed by the opening of the backarc basins of the southwest Pacific and the migration of theTonga andKermadec Trenchs to the east.[31] Shear extrusion followed between 23.3 million to 5 million years ago with the New ZealandAlpine Fault rupture and a southwestward extension of theCampbell Plateau relative to theChallenger Plateau.[30] Southeast Indian Ocean Ridge expansion movement completely separated Zealandia from the Antarctic at about 10 million years ago.[30] In the last 5 million years Zealandia has been generally subsiding owing to the Pacific Plate subducting westward and retreating eastward.[30]
New Caledonia is at the northern end of the ancient continent, while New Zealand rises at the plate boundary that bisects it. These land masses constitute two outposts of theAntarctic flora, featuringaraucarias andpodocarps. AtCurio Bay, logs of afossilizedforest closely related to modernkauri andNorfolk pine can be seen that grew on Zealandia approximately 180 million years ago during theJurassic period, before it split from Gondwana.[32] The trees growing in these forests were buried by volcanic mud flows and gradually replaced bysilica to produce the fossils now exposed by the sea.
As sea levels drop during glacial periods, more of Zealandia becomes aterrestrial environment rather than a marine environment. Originally, it was thought that Zealandia had no native landmammal fauna, butthe discovery in 2006 of a fossil mammal jaw from theMiocene in theOtago region demonstrates otherwise.[33]
As of 2024,[update] the total human population of Zealandia is approximately 5.4 million people. The largest city isAuckland with about 1.7 million people; roughly one-third of the total population of the continent.
^"Searching for the lost continent of Zealandia".TheDominion Post. 29 September 2007. Retrieved9 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.
^Campbell, Hamish; Gerard Hutching (2007).In Search of Ancient New Zealand. North Shore, New Zealand:Penguin Books. pp. 166–167.ISBN978-0-14-302088-2.
^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 fromthe original(PDF) on 21 February 2007. Retrieved22 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.
^Adams, C; Ramsay, W (2022). "Archean and Paleoproterozoic zircons in Paleozoic sandstones in southern New Zealand: evidence for remnant Nuna supercontinent and Ur continent rocks within Zealandia".Australian Journal of Earth Sciences.69 (8):1061–1081.Bibcode:2022AuJES..69.1061A.doi:10.1080/08120099.2022.2091039.S2CID251000288.
^Campbell, Hamish; Gerard Hutching (2007).In Search of Ancient New Zealand. North Shore, New Zealand: Penguin Books. pp. 183–184.ISBN978-0-14-302088-2.
