in the origin of the Pacific Ocean's volcanic Ring of Fire. Geological Subdivisons 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 Median Batholith crust. These two features are separated by the Alpine Fault and Kermadec Trench and by the wedge-shaped Hikurangi Plateau, and they are moving separately to each other. 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 2014 book, entitled Zealandia: Our continent revealed, 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 submerged continent, rather than a microcontinent or continental fragment. This verdict was widely covered by news media. Oldest parent rocks The younger Zealandia rocks have evidence of origins from early Gondwana formations of 500 to 700 million years ago, Rodinia formations about a billion years ago and sources from an expanded-Ur continent between 3.5 to 2 billion years ago. Tectonics The breakup of Gondwana formed Northern Zealandia. Zealandia underwent extension resulting from east to northeast-directed rollback of west to southwest-dipping subduction of the Pacific Plate. which terminated between 95 million to 85 million years ago. After 85 million years ago Zealandia separated from Australia through seafloor spreading of the Coral and Tasman seas until this ceased 52 million years ago. Shortening on an active convergent northern margin of Zealandia occurred mainly between 45 to 35 million years ago. This was followed by the opening of the backarc basins of the southwest Pacific and the migration of the Tonga and Kermadec Trenchs to the east. Shear extrusion followed between 23.3 million to 5 million years ago with the New Zealand Alpine Fault rupture and a southwestward extension of the Campbell Plateau relative to the Challenger Plateau. Southeast Indian Ocean Ridge expansion movement completely separated Zealandia from the Antarctic at about 10 million years ago. In the last 5 million years Zealandia has been generally subsiding owning to the Pacific Plate subducting westward and retreating eastward. Attribution History Copied content for back inclusion from Zealandia; see that page's history for attribution. References Geology of Zealandia Geology of Oceania