Zealandia

Zealandia (pronounced /ziːˈlændiə/), also known as Te Riu-a-Māui (Māori)[2] or Tasmantis (from Tasman Sea),[3][4] is an almost entirely submerged mass of continental crust in Oceania that subsided after breaking away from Gondwana 83–79 million years ago.

[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.

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.

In the Māori language, the landmass is named Te Riu-a-Māui, meaning 'the hills, valleys, and plains of Māui'.

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's mantle as that of most landmasses.

[citation needed] Volcanism on Zealandia has taken place repeatedly in various parts of the continental fragment before, during, and after it rifted away from the supercontinent Gondwana.

[21] This volcanism is widespread across Zealandia, but on present land generally it is of low volume apart from the huge mid to late Miocene shield volcanoes that developed the Banks and Otago Peninsulas.

[24] 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 submerged continent, rather than a microcontinent or continental fragment.

[29] Zealandia underwent extension resulting from east to northeast-directed rollback of west to southwest-dipping subduction of the Pacific Plate.

[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.

At Curio Bay, logs of a fossilized forest closely related to modern kauri and Norfolk pine can be seen that grew on Zealandia approximately 180 million years ago during the Jurassic period, before it split from Gondwana.

[32] The trees growing in these forests were buried by volcanic mud flows and gradually replaced by silica to produce the fossils now exposed by the sea.