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 ...
, (after
Ontong Java
Ontong Java Atoll or Luangiua, (formerly ''Lord Howe Atoll'', not to be confused with Lord Howe Island) is one of the largest atolls on earth.
Geographically it belongs to a scattered group of three atolls which includes nearby Nukumanu Atol ...
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 contine ...
east of Japan. 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 formation ...
Ontong Java
Ontong Java Atoll or Luangiua, (formerly ''Lord Howe Atoll'', not to be confused with Lord Howe Island) is one of the largest atolls on earth.
Geographically it belongs to a scattered group of three atolls which includes nearby Nukumanu Atol ...
-
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 ...
- Hikurangi.
It was named for Nikolay Shatsky (1895-1960), a Soviet geologist, expert in tectonics of ancient platforms.
The rise consists of three large volcanic massifs, Tamu, Ori, and Shirshov, but, in contrast, there are few traces of magmatism on the surrounding ocean floor.
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 Olympus Mons in terms of surface area.
Extent and volume
It covers an area that has been estimated to (roughly the size of
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...
or Sumatra) and a volume of .
Beneath Shatsky rise, however, the
Mohorovičić discontinuity
The Mohorovičić discontinuity ( , ), usually referred to as the Moho discontinuity or the Moho, is the boundary between the Earth's crust and the mantle. It is defined by the distinct change in velocity of seismic waves as they pass through ch ...
(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 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 dive ...
(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 definition, to Antarctica) in the south, and is bounded by the continen ...
Izanagi
Izanagi (イザナギ/伊邪那岐/伊弉諾) or Izanaki (イザナキ), formally known as
, is the creator deity (''kami'') of both creation and life in Japanese mythology. He and his sister-wife Izanami are the last of the seven generations of ...
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 ...
, 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 a planet's 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 field has alternated be ...
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 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 ...
. 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
The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the w ...
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, 70 to 80 million years ago, and ended 35 to 55 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.