oceanic plateau
An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides.
There are 184 oceanic plateaus in the world, covering an area of or about 5.11% of the o ...
, (after
Ontong Java
Ontong Java Atoll or Luangiua (formerly Lord Howe Atoll, not to be confused with Lord Howe Island) is an atoll in the Solomon Islands, and one of the largest atolls on earth.
It is inhabited by a Polynesian community of about people, who spe ...
and
Kerguelen
The Kerguelen Islands ( or ; in French commonly ' but officially ', ), also known as the Desolation Islands (' in French), are a group of islands in the sub-Antarctic region. They are among the most isolated places on Earth, with the closest t ...
) located in the north-west
Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...
east of
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
. It is one of a series of Pacific Cretaceous
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 format ...
Ontong Java
Ontong Java Atoll or Luangiua (formerly Lord Howe Atoll, not to be confused with Lord Howe Island) is an atoll in the Solomon Islands, and one of the largest atolls on earth.
It is inhabited by a Polynesian community of about people, who spe ...
-
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, ...
-
Hikurangi
Hikurangi is a settlement in Northland Region, Northland, New Zealand. The city of Whangārei is to the south, and Kawakawa, New Zealand, Kawakawa is northwest. The Glenbervie Forest is southeast of the settlement. New Zealand State Highway ...
.
It was named for
Nikolay Shatsky
Nikolay Sergeyevich Shatsky, also spelt Nicholas Shatski (; in Moscow – August 1, 1960 in Moscow) was a Soviet Union, Soviet geologist, an expert in tectonics of ancient platform (geology), platforms.
Tamu Massif
Tamu Massif is a seamount in the northwest Pacific Ocean, sitting atop a triple junction of mid-ocean ridges. Tamu Massif is located in the Shatsky Rise about east of Japan. The massif covers an area of about . Its summit is about below the s ...
is likely the largest volcano yet discovered on Earth. In 2016, a study found that Tamu Massif covered the entire Shatsky Rise, meaning that the volcano had a surface area of , surpassing
Olympus Mons
Olympus Mons (; ) is a large shield volcano on Mars. It is over high as measured by the Mars Orbiter Laser Altimeter (MOLA), about 2.5 times the elevation of Mount Everest above sea level. It is Mars's tallest volcano, its tallest planetary mou ...
in terms of surface area.
Extent and volume
The central area of the Shatsky Rise is a diagonal plateau that extends from about 32–38° N. and 156–164° E. Including its periphery and the Papanin Ridge, it reaches from about 30–44° N. and 154–168° E. It covers an area that has been estimated to (roughly the size of
California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
or
Sumatra
Sumatra () is one of the Sunda Islands of western Indonesia. It is the largest island that is fully within Indonesian territory, as well as the list of islands by area, sixth-largest island in the world at 482,286.55 km2 (182,812 mi. ...
) and a volume of . Beneath Shatsky rise, however, the
Mohorovičić discontinuity
The Mohorovičić discontinuity ( ; )usually called the Moho discontinuity, Moho boundary, or just Mohois the boundary between the Earth's crust, crust and the Earth's mantle, mantle of Earth. It is defined by the distinct change in velocity of s ...
(Moho, the mantle-crust boundary) disappears at a depth of whereas it is normally observed at a depth of . Furthermore, the crustal thickness between the massifs of the Shatsky Rise is almost twice that of normal crust thickness. This considered, the area covered by the rise, assuming the crust was also formed by the Shatsky Rise volcanism, has been estimated to and the volume to .
Subsidence
After its formation Shatsky Rise was uplifted and it then subsided , which, in both cases, is considerably more than the Ontong-Java Plateau. There was least subsidence at the centre of the Tamu Massif ( ), subsidence increased at the northern flank of the Tamu Massif and at the Ori Massif ( ), and it becomes greatest at the flank of Ori Massif. The cause of this gradual increase in subsidence can be
underplating
Magmatic underplating occurs when basaltic magmas are trapped during their rise to the surface at the Mohorovičić discontinuity or within the crust. Entrapment (or 'stalling out') of magmas within the crust occurs due to the difference in rel ...
beneath Tamu Massif. There was much less subsidence at Shirshov Massif farther north ( ) which probably represents a later, different phase of volcanism.
Origin controversy
Scientific studies of the size, shape, and eruption rate of the Shatsky Rise have concluded that the rise originated from a mantle plume, whereas studies of magnetic lineations and plate tectonic reconstructions have shown that it must have originated near a triple junction and drifted up to during the Early Cretaceous (140–100 Ma). A 2016 study concluded that the Tamu Massif formed at a mid-ocean ridge that interacted with a plume head and that the Ori Massif formed off-axis probably from a plume tail.
Shatsky Rise formed at a triple junction, but the thickness of the plateau coupled with the depth and intensity of melting is different from those of
MORB
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 div ...
(mid-ocean ridge basalt), making a recycled mantle slab a more likely source. A decrease in magma volume with time is more consistent with the involvement of a mantle plume.
Tectonic history
It formed during the Late Jurassic and Early Cretaceous at the
Pacific
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 the definition, to Antarctica in the south, and is bounded by the cont ...
Izanagi
Izanagi (イザナギ/伊邪那岐/伊弉諾) or Izanaki (イザナキ), formally referred to with a divine honorific as
, is the creator deity (''kami'') of both creation and life in Japanese mythology. He and his sister-wife Izanami are the ...
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 be ...
, probably making it the oldest unaltered ocean plateau. Because this occurred before the so-called Cretaceous silent period, a long period without
magnetic reversal
A geomagnetic reversal is a change in the Earth's dipole magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's magnetic fi ...
s, its formation can be precisely dated.
Magnetic lineations on and surrounding Shatsky Rise range from M21 (147 Ma) at the south-western edge to M1 (124 Ma) at the northern tip.
The Shatsky Rise LIP erupted at the location of the Pacific–Farallon–Izanagi triple junction 147–143 Ma either because a mantle plume reached the surface or because of decompression melting at a
mid-ocean ridge
A mid-ocean ridge (MOR) is a undersea mountain range, 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 ...
. The eruption coincided with an , nine-stage jump in the location of the triple junction and a configuration change from ridge-ridge-ridge to ridge-ridge-transform.
A set of magnetic lineations, called the Hawaiian lineations, between Shatsky Rise, Hess Rise, and the
Mid-Pacific Mountains
The Mid-Pacific Mountains (MPM) is a large oceanic plateau located in the central North Pacific Ocean or south of the Hawaiian–Emperor seamount chain. Of volcanic origin and Mesozoic in age, it is located on the oldest part of the Pacific Plat ...
, formed during the spreading between the Pacific and Farallon plates 156–120 Ma. North of Shatsky Rise the so-called Japanese lineations are oriented in another direction and the differences in orientations trace the path of the Pacific–Farallon–Izanagi triple junction.
The triple junction moved north-west before M22 (150 Ma) after-which it started to reorganise, a microplate formed and the triple junction made an eastward jump to the oldest part of the rise, the TAMU Massif. The remainder of Shatsky Rise formed before M3 (126 Ma) along the trace of the triple junction. Shaktsky volcanism was episodic and tied to at least nine ridge jumps from this episode.
The volume of the rise decreases along the trace of the triple junction. The TAMU Massif at the southern end has an estimated volume of whereas both ORI and Shirshov (136 Ma) attained . Papanin Ridge, the north end of the rise, has a volume of but was probably emplaced over a longer period (131–124 Ma).
The conjugates of the Shatsky and Hess rises on the Farallon Plate were most likely involved in the
Laramide orogeny
The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 80 to 70 million years ago, and ended 55 to 35 million years ago. The exact duration and ages of beginning and end of the o ...
; the former subducted beneath North America and the latter below northern Mexico.