ⓘ Zealandia

                                     

ⓘ Zealandia

Zealandia, also known as the New Zealand continent or Tasmantis, is an almost entirely submerged mass of continental crust that subsided after breaking away from Gondwanaland 83–79 million years ago. It has variously been described as a continental fragment, a microcontinent, a submerged continent, and a continent. The name and concept for Zealandia was proposed by Bruce Luyendyk in 1995.

The land mass may have been completely submerged by about 23 million years ago, and most of it 93% remains submerged beneath the Pacific Ocean. With a total area of 4.920.000 km 2 1.900.000 sq mi, it is the worlds 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. This was the argument which made news in 2017, 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. New Zealand geologist Nick Mortimer has commented that "if it wasnt for the ocean" it would have been recognized as such long ago.

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

                                     

1. Geology

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 the Earths 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. 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.

                                     

1.1. Geology 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, citing geological and ecological evidence to support the proposal.

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

                                     

2. 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. 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.

                                     

3. Political divisions

The total land area including inland water bodies of Zealandia is 286.655 km 2 110.678 sq mi. Of this, New Zealand comprises the majority, at 267.988 km 2 103.471 sq mi, or 93% which includes the mainland, nearby islands, and most outlying islands including the Antipodes Islands, Auckland Islands, Bounty Islands, Campbell Islands, and Chatham 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 km 2 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 km 22 sq mi or 0.02%, Norfolk Island at 35 km 2 14 sq mi or 0.01%, as well as the Elizabeth and Middleton Reefs Coral Sea Islands Territory with 0.25 km 2 0.097 sq mi.

                                     

4. Population

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

  • New Zealand – 4.823.193
  • Lord Howe Island Group – 382
  • Norfolk Island – 2.210
  • Elizabeth and Middleton Reefs – 0
  • New Caledonia – 268.767
                                     
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