Zealandia , also known as Tasmantis or the New Zealand continent, is a nearly
submerged continental fragment that sank after breaking away from Australia 60–85
Ma ago, having separated from Antarctica between 85 and 130 Ma ago. It may have
been completely submerged about 23 Ma ago, and most of it remains submerged
beneath the Pacific Ocean. Description
Zealandia is 3.5 million square km in area, almost half the size of Australia.
It is unusually slender, stretching from New Caledonia in the north to beyond New
Zealand's subantarctic islands in the south. New Zealand is the largest part
of Zealandia above sea level, followed by New Caledonia.
The major submerged parts of Zealandia are the Lord Howe Rise, Challenger
Plateau, Campbell Plateau, Norfolk Ridge, and the Chatham Rise. Smaller
provinces include the Louisiade Plateau, Mellish Rise, Kenn Plateau, Chesterfield
Plateau, and Dampier Ridge. The seemingly separate Gilbert Seamount is
also part of the New Zealand continental fragment, while how strongly Bollons
Seamount remains connected to Zealandia is unknown.
Zealandia supports substantial inshore fisheries and contains New Zealand's
largest 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.
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, with infrequent 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
thick, and consequently they do not float as high above the Earth's mantle.
About 25 Ma, the southern part of Zealandia began to shift relative to the
northern part. The resulting displacement by approximately 500 km
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. Further 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 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 might have slid over a
stationary hotspot, forming the Lord Howe seamount chain.
Zealandia is occasionally divided by scientists into two regions, North
Zealandia and South Zealandia, 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. 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 a recent
discovery in 2006 of a fossil mammal jaw from the Miocene in the Otago region
shows otherwise. Political divisions
New Zealand – 267,988 km2 Includes the mainland, nearby islands,
and most outlying islands including the Antipodes Islands, Auckland Islands,
Bounty Islands, Campbell Islands, and Chatham Islands, which are part of the
rift) New Caledonia and surrounding islands –
18,576 km2 Various territories of Australia
Lord Howe Island Group – 56 km2 Norfolk Island – 35 km2
Elizabeth and Middleton Reefs – 0.25 km2 Total land area: ~ 286,655 km2
Population New Zealand – 4,430,400
New Caledonia – 252,000 Norfolk Island – 2,302
Lord Howe Island Group – 347 Elizabeth and Middleton Reefs – 0
Total population: 4,685,000 References
External links Zealandia the New Zealand Continent,
from Te Ara