Zealandia (), also known as Te Riu-a-Māui (Māori) 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 submerged continent, a continental fragment, a microcontinent, and a continent.The name and concept for Zealandia was proposed by Bruce Luyendyk in 1995.The landmass may have been completely submerged by about 23 million years ago, and most of it (94%) remains submerged beneath the Pacific Ocean. New Zealand is the largest part of Zealandia that is above sea level, followed by New Caledonia.
With a total area of approx. 4,900,000 km2 (1,900,000 sq mi), Zealandia is substantially bigger 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 Madagascar, the next-largest microcontinent in the world, and more than half the area of the Australian continent. Zealandia is more than twice the size of the largest intraoceanic large igneous province (LIP) in the world, the Ontong Java Plateau (approx. 1,900,000 km2 (730,000 sq mi)), and the world's biggest island, Greenland (2,166,086 km2 (836,330 sq mi)). Zealandia is also substantially bigger than the Arabian Peninsula (3,237,500 km2 (1,250,000 sq mi)), the world's largest peninsula, and the Indian subcontinent (4,300,000 km2 (1,700,000 sq mi)). Due to these and other geological considerations, such as crustal thickness and density, 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. English-born New Zealand geologist Nick Mortimer (in German) commented that "if it wasn't 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 Zealand's Maui gas field, near Taranaki. Permits for oil exploration in the Great South Basin were issued in 2007. Offshore mineral resources include ironsands, volcanic massive sulfides and ferromanganese nodule deposits.