The Manihiki Plateau is an oceanic plateau in the south-west

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

. The Manihiki Plateau was formed by volcanic activity 125 to 120 million years ago during the mid-

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

period at a

triple junction A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of three types – a ridge (R), trench (T) or transform fault (F) – and triple junctions can ...

plate boundary called the

Tongareva triple junction The Tongareva triple junction, also called the Pacific-Farallon-Phoenix triple junction, was a geologic triple junction in the southwestern Pacific Basin where three tectonic plates met: the Pacific Plate, the Farallon Plate, and the Phoenix Plate ...

. 125 million years ago the Manihiki Plateau formed part of the giant Ontong Java-Manihiki-

Hikurangi Hikurangi is a settlement in Northland, New Zealand. The city of Whangārei is 17 km (11 miles) to the south, and Kawakawa is 39 km (24 miles) northwest. The Glenbervie Forest is southeast of the settlement. State Highway ...

plateau.

Geological setting

The Manihiki Plateau extends from 3°S to 6°S and 159°W to 169°W covering and has an estimated volume of with a crustal thickness of . Several of the

Cook Islands ) , image_map = Cook Islands on the globe (small islands magnified) (Polynesia centered).svg , capital = Avarua , coordinates = , largest_city = Avarua , official_languages = , lan ...

are located on the southern part:

Danger Danger is a lack of safety and may refer to: Places * Danger Cave, an archaeological site in Utah * Danger Island, Great Chagos Bank, Indian Ocean * Danger Island, alternate name of Pukapuka Atoll in the Cook Islands, Pacific Ocean * Danger Isla ...

, Nassau, Suvorov,

Rakahanga Rakahanga is part of the Cook Islands, situated in the central-southern Pacific Ocean. The unspoilt atoll is from the Cook Islands' capital, Rarotonga, and lies south of the equator. Its nearest neighbour is Manihiki which is just away. Raka ...

, and

Manihiki 250px, Map of Manihiki Atoll Manihiki is an atoll in the northern group of the Cook Islands known informally as the "Island of Pearls". It is located in the Northern Cook Island chain, approximately north of the capital island of Rarotonga, ma ...

. The Tokelau Basin borders it to the west, the Samoan Basin to the south, the Penrhyn Basin to the east, and the Central Pacific Basin to the north. It reaches up to below sea level, several kilometres shallower than the surrounding basins. The plateau can be divided into three regions. The south-eastern High Plateau is the shallowest and flattest; its basement is covered by up to a kilometre of pelagic sedimentary rock. The Western Plateaus, north-west of the High Plateau, are a series of ridges and seamounts. The North Plateau is small and almost separated from the rest of the Manihiki Plateau. The High Plateau is the largest part of Manihiki covering above 4000 m. The second largest part is the Western Plateaus covering above 5000 m and reaching below sea level. The smallest part, the North Plateau, covers above 4500 m and reaches . These plateaus are separated by failed rifts.

Tectonic evolution

The Manihiki Plateau was originally described as a subsided microcontinent in 1966, but has been known to be made of oceanic crust since DSDP drillings were made in the 1970s. The formation of the plateau is related to the intense volcanism of the Early Cretaceous and

mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a diver ...

jumps. A hotspot and several mantle sources were involved in the formation of the Manihiki

large igneous province A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...

(LIP). 121–119 Ma it was the largest oceanic plateau on Earth, twice its present size, when a triple junction originated in its north-western corner, splitting it into three parts. The modern Manihiki Plateau rifted from the Hikurangi Plateau, now located adjacent to New Zealand, in the Early Cretaceous. In the Early Cretaceous the Manihiki Plateau was much shallower, below sea level or less. Shortly after emplacement the initiation of the Tongareva triple junction resulted in extension,

upwelling Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nut ...

and rifting. Renewed rifting at about 116 Ma created the eastern margin, the Manihiki Scarp, and separated Manihiki and Hikurangi. The Osbourn Trough is an abandoned spreading centre between Manihiki and Hikurangi. Other Cretaceous LIPs in the Pacific, except Ontong Java and Hikurangi, include the Hess, Shatsky and Magellan rises.

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