Takuyo-Daisan

Takuyo-Daisan was formerly known as "Seiko guyot";^[1] "Seiko guyot" was used even earlier for Takuyo-Daini while Takuyo-Daisan was named "Eiko".^[2] This seamount was drilled by the Ocean Drilling Program, with Site 879 located on the seamount.^[3]

Takuyo-Daisan lies southeast of the city of Yokohama, Japan.^[4] It is the easternmost seamount in the "Seiko" cluster^[5] of the Japanese Seamounts.^[3] The Boso triple junction lies only 200 kilometres (120 mi) away from the seamount.^[2]

Takuyo-Daisan is a guyot^[6] that rises to a minimum depth of 1,409 metres (4,623 ft)^[7] and is capped by an approximately square-shaped surface platform at about 1,600 metres (5,200 ft) depth^[8] which has a surface area of about 86 square kilometres (33 sq mi).^[7] Depressions up to 75 metres (246 ft) deep cover the flat top. The top is surrounded by a 0.6–1 kilometre (0.37–0.62 mi) wide and up to 110 metres (360 ft) high ridge, especially on the northeastern and southern sides.^[9] It may be either a bioherm or a karst landform. A 100 metres (330 ft)^[10]-110 metres (360 ft) high structure may be part of the old volcanic edifice;^[6] the interface between the carbonate platform and the volcanic basement has a sloping aspect.^[11]

Away from the platform, the seamount has steep slopes probably formed by short lava flows^[6] that rise 4.3 kilometres (2.7 mi) above the seafloor.^[12] Channels, debris flow fronts and levees decorate its slopes.^[13] Noticeable ridges emanate from the east-southeastern, southwestern, west-northwestern and north-northeastern corners of the seamount;^[8] they appear to be rift zones,^[14] and flank cones are found on the eastern slopes. The southern slopes feature slump deposits, and the entire seamount is surrounded by a sediment fan.^[13] The volume of the entire seamount is about 1,300 cubic kilometres (310 cu mi).^[15] Two large seamounts lie west and southwest of Takuyo-Daisan with a smaller seamount between the two;^[14] Takuyo-Daini is the western one and Jensen seamount the south-western one.^[13] The seafloor underneath Takuyo-Daisan has an age of 143 million years.^[16]

The Western Pacific Ocean features many seamounts with flat tops at depths of 1–2 kilometres (0.62–1.24 mi) below sea level which are known as guyots. They were considered to be remnants of eroded islands before Cretaceous carbonate platforms were discovered on them^[5] which resemble present-day atolls although they do not have exactly the same properties.^[12] Later similar submarine mountains were identified elsewhere in the Pacific Ocean as well. Menard 1958 suggested that the Western Pacific guyots once were part of an elevated region known as the Darwin Rise, later compared to present day French Polynesia.^[4]

Many of these seamounts originally formed in the South Pacific, such as in French Polynesia,^[17][18] where a number of recent volcanoes and volcanic chains can be found.^[17] The original location of Takuyo-Daisan closely matches the present-day location of the Society hotspot,^[19] and together with Takuyo-Daini, Winterer Guyot and Isakov Guyot appears to form a linear volcanic chain,^[20] the Geisha guyots.^[21]

Takuyo-Daisan has erupted basalt^[22] containing olivine and plagioclase^[23] and which define an intermediary to tholeiitic magma suite.^[24] Weathering of volcanic rocks has given rise to calcite,^[23] clay^[10] which also contains coal,^[25] iddingsite and zeolite.^[23] Carbonates occur in the form of floatstone, grainstone, limestone, packstone, oncoids, peloids, rudstone and wackestone;^[26] the limestone is of reefal origin. Hypersthene andesite samples taken from Takuyo-Daisan were probably brought there by ice rafting^[27] as no such rocks have ever been found on this kind of volcanic island.^[28]