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35-475: 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 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 533,000 square kilometres (206,000 sq mi), surpassing Olympus Mons in terms of surface area. The central area of

70-403: A characteristic influenced by the presence of oceanic plateaus (or oceanic flood basalts). In addition to influencing slab buoyancy, some oceanic plateaus may have also become accreted to North America. It has been suggested that this deformation may go so far as to include a tear in the slab, where a piece of the subducted Farallon plate has broken off, creating multiple slab remnants. This

105-602: 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 , 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

140-477: 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 (mid-ocean ridge basalt), making a recycled mantle slab a more likely source. A decrease in magma volume with time is more consistent with

175-497: 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 1,600 km (990 mi) east of Japan . The massif covers an area of about 553,000 square kilometres (214,000 sq mi). Its summit is about 1,980 m (6,500 ft) below the surface of the ocean, and its base extends to about 6.4 km (4.0 mi) deep. It

210-476: Is a large mountain or a section of the planet's crust that is demarcated by faults and flexures. The Tamu Massif was formed about 145 million years ago during the Late Jurassic to Early Cretaceous period over a relatively short period of time (a few million years) and then became extinct. Tamu Massif was formed during a single geologically brief eruptive period, which scientists had previously thought

245-591: Is about 4,460 metres (14,620 ft) tall. William Sager , a marine geophysicist from the Department of Earth and Atmospheric Sciences at the University of Houston , began studying Tamu Massif around 1993 at the Texas A&;M College of Geosciences . In September 2013, Sager and his team concluded that Tamu Massif is "the biggest single shield volcano ever discovered on Earth". Other igneous features on

280-543: Is supported by tomography studies and provides some more explanation of the formation of Laramide structures that are further inland from the edge. A 2013 study proposed two additional now-subducted plates that would account for some of the unexplained complexities of the accreted terranes, suggesting that the Farallon should be partitioned into Northern Farallon, Angayucham , Mezcalera and Southern Farallon segments based on recent tomographic models. Under this model,

315-604: The Mohorovičić discontinuity (Moho, the mantle-crust boundary) disappears at a depth of 20 km (12 mi) whereas it is normally observed at a depth of 17 km (11 mi). 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 533,000 km (206,000 sq mi) and

350-640: The North American plate ; the Cocos plate subducting under Central America ; and the Nazca plate subducting under the South American plate . The Farallon plate is also responsible for transporting old island arcs and various fragments of continental crust , which have rifted off of other distant plates. These fragments from elsewhere are called terranes (sometimes, "exotic" terranes). During

385-451: The convergent plate boundary than is typical of a subduction-generated orogeny . Significant deformation of the slab also occurred due to this flat subduction phenomenon, which has been imaged by seismic tomography. There is a concentration of velocity anomalies in the tomography that is thicker than the slab itself should be, indicating that folding and deformation occurred beneath the surface during subduction. In other words, more of

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420-413: The plume-head model indicates a single massive volcano. Based on multichannel seismic profiles and rock samples from Integrated Ocean Drilling Program (IODP) core sites, Tamu Massif appears to be a single massive volcano made of lava flows that emanated from the volcano centre and formed its shield shape; however, the profiles have large gaps in them, leaving open the possibility that it may represent

455-606: The Farallon slab appears as a velocity anomaly on the tomography model. Multiple studies show that the subduction of the Farallon plate was characterized by a period of " flat-slab subduction ," which is the subduction of a plate at a relatively shallow angle to the overriding crust (in this case, North America). This phenomenon is one that accounts for the far-inland orogenisis of the Rocky Mountains and other ranges in North America which are much farther from

490-482: The North American continent overrode a series of subduction trenches, and several microcontinents (similar to those in the modern-day Indonesian Archipelago ) were added to it. These microcontinents must have had adjacent oceanic plates that are not represented in previous models of Farallon subduction, so this interpretation brings forth a different perspective on the history of collision. Based on this model,

525-533: 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 c. 480,000 km (190,000 sq mi) (roughly the size of California or Sumatra ) and a volume of c. 4,300,000 km (1,000,000 cu mi). Beneath Shatsky rise, however,

560-438: The activity of more than one volcano. A subsequent study in 2016 found that the massif was likely generated by a single volcano. In 2015, researchers found that the volcano's structure bore patterns of magnetic striping on either side, indicating that the volcano is likely a hybrid of a mid-ocean ridge and a shield volcano . Geologic data also indicated that Tamu Massif formed at the junction of three mid-ocean ridges, which

595-538: The area of the Martian volcano Olympus Mons . The entire mass of Tamu consists of basalt . Its slopes are very gradual, ranging from less than half a degree to one degree near its summit. The Shatsky Rise oceanic plateau is comparable in size to California or Japan , but Tamu Massif, which is the plateau's oldest and largest edifice, is comparable in size to New Mexico , or Britain and Ireland together. A study in 2016 found that Tamu Massif likely encompassed

630-420: The entire Shatsky Rise, meaning that Tamu Massif has an area of about 533,000 square kilometres (206,000 sq mi), surpassing Olympus Mons in surface area, though it has not yet been determined which of the two volcanoes has a greater mass. Using magnetic lineations , researchers discovered that there are three bathymetric highs and a low ridge, a topography that would imply three separate volcanoes; but

665-557: The involvement of a mantle plume. It formed during the Late Jurassic and Early Cretaceous at the Pacific – Farallon – Izanagi triple junction , probably making it the oldest unaltered ocean plateau. Because this occurred before the so-called Cretaceous silent period, a long period without magnetic reversals , its formation can be precisely dated. Magnetic lineations on and surrounding Shatsky Rise range from M21 (147 Ma) at

700-496: The northern flank of the Tamu Massif and at the Ori Massif ( c. 3,300 m (10,800 ft)), 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 ( c. 2,900 m (9,500 ft)) which probably represents a later, different phase of volcanism. Scientific studies of

735-549: 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 800 km (500 mi) 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

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770-540: The planet are larger, such as the Ontong Java Plateau , but it has not yet been determined if they are indeed just one volcano or rather complexes of several volcanoes. The name Tamu is taken from the initials of Texas A&M University . William Sager, a geology professor and one of the lead scientists studying the volcano, previously taught at Texas A&M. A massif , which means "massive" in French,

805-457: The plate moved west, causing the following geologic events to occur: When the final archipelago , the Siletzia archipelago, lodged as a terrane, the associated trench stepped west. When this happened, the trench that had been characterized as an oceanic-oceanic subduction environment approached the North American margin and eventually became the current Cascadia subduction zone . This created

840-469: 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 2,000 km (1,200 mi) during the Early Cretaceous (140–100 Ma). A 2016 study concluded that the Tamu Massif formed at

875-420: The slab should be in the lower mantle, but the deformation has caused it to remain shallower, in the upper mantle. Multiple hypotheses have been proposed to explain this shallow subduction angle and resulting deformation. Some studies suggest that the faster movement of the North American plate caused the slab to flatten, resulting in slab rollback . Another cause of flat slab subduction may be slab buoyancy ,

910-409: 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 c. 147–143 Ma either because a mantle plume reached the surface or because of decompression melting at a mid-ocean ridge . The eruption coincided with an 800 km (500 mi), nine-stage jump in the location of the triple junction and

945-497: The subduction of the Farallon plate, it accreted these island arcs and terranes to the North American plate . Much of western North America is composed of these accreted terranes. As an ancient tectonic plate, the Farallon plate must be studied using methods that allow researchers to see deep beneath the Earth's surface. The understanding of the Farallon plate has evolved as details from seismic tomography provide improved details of

980-461: The submerged remnants. Since the North American west coast has a convoluted structure, significant work has been required to resolve the complexity. Seismic tomography can be used to image the remainder of the subducted plate because it is still "cold," as in, it has not reached thermal equilibrium with the mantle. This is important for the use of tomography because seismic waves have different velocities in materials of different temperatures, so

1015-595: The triple junction during the Early Jurassic . It is named for the Farallon Islands , which are located just west of San Francisco , California . Over time, the central part of the Farallon plate was subducted under the southwestern part of the North American plate. The remains of the Farallon plate are the Explorer , Gorda , and Juan de Fuca plates, which are subducting under the northern part of

1050-482: The volume to 6,900,000 km (1,700,000 cu mi). After its formation Shatsky Rise was uplifted 2,500–3,500 m (8,200–11,500 ft) and it then subsided 2,600–3,400 m (8,500–11,200 ft), which, in both cases, is considerably more than the Ontong-Java Plateau. There was least subsidence at the centre of the Tamu Massif ( c. 2,600 m (8,500 ft)), subsidence increased at

1085-462: Was a highly unusual occurrence. A study found that the Moho line , the boundary between the Earth's crust and mantle, extends more than 30 kilometres (19 mi) beneath the base of Tamu Massif, meaning that the volcano is unlikely to ever erupt again, since magma is presumably unable to penetrate a barrier that thick. Informational notes Citations Farallon Plate The Farallon plate

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1120-515: Was an ancient oceanic tectonic plate . It formed one of the three main plates of Panthalassa , alongside the Izanagi plate and the Phoenix plate , which were connected by a triple junction . The Farallon plate began subducting under the west coast of the North American plate —then located in modern Utah —as Pangaea broke apart and after the formation of the Pacific plate at the center of

1155-504: 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 2,500,000 km (600,000 cu mi) whereas both ORI and Shirshov (136 Ma) attained 700,000 km (170,000 cu mi). Papanin Ridge, the north end of the rise, has a volume of 400,000 km (96,000 cu mi) but

1190-597: Was impossible on Earth. If confirmed, the suggestion that it could be a single volcano would make the Tamu Massif the largest known volcano on Earth , dwarfing the current record-holder, Pūhāhonu , in the Hawaiian Islands . The main part of Tamu's rounded dome extends over an area of 450 km × 650 km (280 mi × 400 mi), totaling more than 292,500 km (112,900 sq mi), many times larger than Mauna Loa, which has an area of 5,000 km (1,900 sq mi), and about half

1225-588: 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 former subducted beneath North America and the latter below northern Mexico. 32°02′00″N 158°04′00″E  /  32.0333°N 158.0667°E  / 32.0333; 158.0667 Tamu Massif Tamu Massif

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