Allison Guyot

Allison Guyot is a tablemount in the underwater Mid-Pacific Mountains of the Pacific Ocean. It is a trapezoidal flat mountain rising 1,500 metres above the seafloor to a depth of less than1,500 m. It was probably formed by a hotspot in the present-day Southern Pacific before plate tectonics moved it to its current location.

About Allison Guyot in brief

Summary Allison GuyotAllison Guyot is a tablemount in the underwater Mid-Pacific Mountains of the Pacific Ocean. It is a trapezoidal flat mountain rising 1,500 metres above the seafloor to a depth of less than1,500 m. The tablemount was probably formed by a hotspot in the present-day Southern Pacific before plate tectonics moved it to its current location. Volcanic activity is dated to have occurred circa 111–85 million years ago and formed a volcanic island. Subsequently, carbonate deposition commenced as Allison Guyot subsided and eventually buried the island, forming an atoll-like structure and a carbonate platform. The platform emerged above sea level during the Albian and Turonian ages. It drowned about 99 ± 2 million years years ago for unknown reasons; possibly a phase of renewed emergence damaged the reefs, or it was located in unfavourable waters. The seamount is the source of the Ocean Drilling Program drill core 865A, which was bored into the summit platform in 1992 but did not reach the volcanic structure of the underwater mountain. The name “Hamilton Guyot” has also been applied to AllisonGuyot but is not correct; Hamilton Guyot is a separate formation in the Mid- Pacific Mountains. All these structures formed as volcanoes in the Mesozoic ocean, though there are some differences to present day reef systems. All of these structures were formerly at seamounts formerly at the middle of the middle-day reef systems, though some are now at lagoons or flats.

Friction of subsidence led to the growth of reefs or flats on these volcanoes, which then became barrier reefs as the volcanoes turned into reefs. Frigid volcanoes tend to cool and sink, and thus the islands and seamsounts sink as the sub-side of the seamountS sink and become islands. The west central and south central Pacific Ocean seafl floor contains many guyots of the Mesozozoic age in seas shallower than typical of thepresent-day ocean shallower than typical of today’s seas. The surface platform has dimensions of 35 by 70 kilometres, with an upwards-doming form 0. 3–0. 5 kilometres high, and is covered by large sediment mounds; the rim surrounding the platform lies at a Depth of about 1,650 metres and there is evidence of former reefs, and the shallowest point of Allison Guyots lies at less than 1,000 metres below sea level. Underneath Allison GuyOT, the Seafloor is about 130–119 million years old, and a 128-million-year-old magnetic lineation is located nearby. The Molokai Fracture Zone forms a ridge which passes close to Allison Guyott and intersects with another ridge at the seamsount. Its western parts may be a distinct volcano, and its western side of the summit plateau has traces of slumping, which on the southeastern side of Allisonguyot has removed part of the platform perimeter.