Geology of the Pacific Ocean

The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.[1]

The tectonic plates continue to move today. The slowest spreading ridge is the Gakkel Ridge on the Arctic Ocean floor, which spreads at less than 2.5 cm/year (1 in/year), while the fastest, the East Pacific Rise near Easter Island, has a spreading rate of over 15 cm/year (6 in/year).

Pacific elevation
The Pacific is ringed by many volcanoes and oceanic trenches
Ulawun
Ulawun stratovolcano situated on the island of New Britain, Papua New Guinea

History

North America subduction
Plate subduction in the North Pacific 70 million years ago

The Pacific Ocean developed from the Panthalassa, a vast global ocean, following the breakup of the supercontinent Pangaea in the Mesozoic Era, gradually forming Gondwana and Laurasia, which in turn divided.[2][3] There is no firm date for when the changeover occurred, as the replacement of the sea bed is a continuous process, though reconstruction maps often change the name from Panthalassic to Pacific around the time the Atlantic Ocean began to open.[4] The Panthalassic Ocean first opened around 750 million years ago at the breakup of Rodinia,[4] but the oldest Pacific Ocean floor is only around 180 Ma old. Any older Pacific floor crust has been subducted.[5]

During the Jurassic period, four tectonic plates developed in the Pacific Basin: the Kula and the Farallon in the north, the large Pacific Plate in the centre and south and the Phoenix Plate in the far south. The Kula Plate was subducted under the eastern and south-eastern Asian landmass. The northern part of the Farallon was subducted under North America while its southern section, together with the Phoenix Plate, was subducted under South America and the Antarctic. During the late Tertiary period, the Farallon plate broke up, leaving the Juan de Fuca Plate in the north, the Cocos Plate off today's Central America, and the Nazca and Phoenix Plates in the southern Pacific.[6][7]

Charles Darwin had proposed a theory of the slow subsidence of the ocean floor based on his studies of Pacific oceanic islands, seamounts (underwater volcanoes) and guyots (flat-topped seamounts). His observations have been verified and expanded in the development of plate tectonic theory.[8]

The tectonic plates continue to move today. The slowest ridge spreading rate is across the Gakkel Ridge in the Arctic Ocean which separates at less than 2.5 cm/yr while the fastest, across the East Pacific Rise near Easter Island, has a spreading rate of over 15 cm/yr.[9] The Pacific Plate moves generally towards the northwest at between 7 and 11 cm/yr while the Juan De Fuca Plate has an east-northeasterly movement of some 4 cm/yr.[10]

Geological origins of the Pacific islands

The theory of plate tectonics, which is supported by seismology, volcanology, gravimetry, and paleomagnetism (remanent magnetism), explains the origin of the physical features of the Pacific.[8] The islands of the Pacific have developed in a number of ways. Some have originated as chains of volcanic islands on the tectonic plates either as a result of mantle plumes or by fracture propagation. Atolls have developed in tropical waters when, after volcanos sink, coral growth results in reefs as evidenced by the Cook Islands. Coral reefs can develop into islands over a submerged extinct volcano following uplift as in Makatea and Rennell Island in the Solomon Archipelago which have steep coral cliffs over 100 metres high.[1]

The collision of two plates, resulting in subduction, have contributed to the emergence of the western Pacific arcs of volcanic islands. A new crust has emerged as the East Pacific Rise. In the northeastern Pacific margin there is a lateral shift, through the San Andreas Fault system, of the North American Plate and the Pacific Plate.[8]

Plate movements have also caused fragments of continental crust to be rotated away from landmasses so as to form islands. Zealandia which broke off from Gondwana 70 million years ago with the spreading of the Tasman Sea, has since resulted in island protrusions such as New Zealand and New Caledonia. Related causes of island formation include obduction and subduction at convergent plate boundaries. Malaita and Ulawa in the Solomon Islands are the result of obduction while the effects of subduction can be seen in the formation of volcanic island arcs such as the Aleutian Arc off Alaska and the Kermadec-Tonga Subduction Zone north of New Zealand.[1]

As a result of the collision of the Nazca Plate and the South American Plate, the Andes Mountains emerged in western South America, close to the Peru–Chile Trench.[8] Many large fracture zones aligned in an east-west direction, occur in the floor of the northeastern Pacific.[8]

Andesite line

The Pacific is a broad ocean basin (unlike the narrow Atlantic Ocean) and extends over a width of 10,000 miles (16,000 km) between New Guinea and Peru.[11] The andesite line, a zone of intense volcanic and seismic activity, is a major regional distinction in the Pacific. The petrologic boundary separates the deeper mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins.[12] The andesite line follows the western edge of the islands off California and passes south of the Aleutian arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, the Solomon Islands, and New Zealand's North Island.[13][14]

The dissimilarity continues northeastward along the western edge of the Andes Cordillera along South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand lie outside the andesite line.

Outside of the andesite line, volcanism is explosive; the Pacific Ring of Fire is the world's foremost belt of explosive volcanism. The Ring of Fire is named after the several hundred active volcanoes that sit above the various subduction zones. In 2009, the deepest undersea eruption ever recorded occurred at the West Mata submarine volcano, a mile beneath the ocean, close to the Tonga-Kermadec Trench, within the Ring of Fire;[15] it was filmed by the US Jason robotic submersible which descended over 1,100 metres (3,600 ft).[16] The Pacific Ocean is the only ocean which is almost totally bounded by subduction zones. Only the Antarctic and Australian coasts have no nearby subduction zones.

Earthquakes

In March and April 2008, a series or swarm of moderate earthquakes occurred both near and within the Blanco Fracture Zone. The swarm began on 30 March when over 600 measurable tremors began occurring north of the zone within the Juan de Fuca Plate.[17] A decade earlier, in January 1998, another swarm was detected at Axial Seamount in the Juan de Fuca Ridge.[18] At the time of its occurrence, scientists were not aware that the series of faults in this plate even existed.[19] In a remote region of the central Pacific Ocean, at the southeastern section of the Gilbert Islands, a major swarm of intraplate earthquakes occurred between December 1981 and March 1983, with no prior seismicity having been reported in this region previously.[20] Another swarm was detected on the Queen Charlotte Islands fracture zone in August–September 1967.[21]

Features

Seamount chains and hotspots

The Pacific Ocean contains several long seamount chains, formed by hotspot volcanism. These include the Hawaiian–Emperor seamount chain, the Tasmantid Seamount Chain, the Lord Howe Seamount Chain and the Louisville Ridge.

Arcs and belts

Faults and fracture zones

Underwater ridges and plateaus

Trenches and troughs

Plates

Volcanoes

References

  1. ^ a b c Neall, Vincent E.; Trewick, Steven A. (27 October 2008). "The age and origin of the Pacific islands: a geological overview". Phil. Trans. R. Soc. B. 363 (1508): 3293–3308. doi:10.1098/rstb.2008.0119. PMC 2607379. PMID 18768382. Retrieved 23 June 2013.
  2. ^ Zhai, M. G. (2007). Mesozoic Sub-Continental Lithospheric: Thinning Under Eastern Asia. Geological Society. pp. 123–. ISBN 978-1-86239-225-0.
  3. ^ Carmen Arias, "Palaeoceanography and biogeography in the Early Jurassic Panthalassa and Tethys Oceans", Universidad Complutense de Madrid. Retrieved 25 June 201.
  4. ^ a b "GEOL 102 The Proterozoic Eon II: Rodinia and Pannotia". Geol.umd.edu. 5 January 2010. Retrieved 23 June 2013.
  5. ^ Mussett, Alan E.; Khan, M. Aftab (2000). Looking into the Earth: An Introduction to Geological Geophysics. Cambridge University Press. p. 332. ISBN 978-0-521-78574-7.
  6. ^ Glasby, G.P. (1989). Antarctic Sector of the Pacific. Elsevier. pp. 131–. ISBN 978-0-08-087089-2.
  7. ^ Foulger, Gillian R.; Jurdy, Donna M. (2007). Plates, Plumes, and Planetary Processes. Geological Society of America. pp. 479–. ISBN 978-0-8137-2430-0.
  8. ^ a b c d e "Pacific Ocean". Geology. Encyclopædia Britannica. Retrieved 26 June 2013.
  9. ^ "Understanding plate motions", USGS. Retrieved 26 June 2013.
  10. ^ "Plate Tectonics", Pacific Northwest Seismic Network. Retrieved 26 June 2013.
  11. ^ Gregory, J. W. (1930). "The Geological History of the Pacific Ocean". Nature. 125 (3159): 750–751. doi:10.1038/125750a0. Retrieved 26 June 2013.
  12. ^ Trent, D. D.; Hazlett, Richard; Bierman, Paul (2010). Geology and the Environment. Cengage Learning. p. 133. ISBN 978-0-538-73755-5.
  13. ^ Mueller-Dombois, Dieter (1998). Vegetation of the Tropical Pacific Islands. Springer. p. 13. ISBN 978-0-387-98313-4.
  14. ^ Lal, Brij Vilash; Fortune, Kate (January 2000). The Pacific Islands: An Encyclopedia. University of Hawaii Press. p. 4. ISBN 978-0-8248-2265-1.
  15. ^ Sandell, Clayton (17 December 2009). "Deepest Undersea Volcanic Eruption Ever Seen". ABC News. Retrieved 26 June 2013.
  16. ^ Amos, Jonathan (18 December 2009). "Deepest volcano caught on Pacific Ocean video – Amazing video has been obtained in the Pacific Ocean of the deepest undersea eruption ever recorded". BBC. Retrieved 26 June 2013.
  17. ^ "2008 Oregon Offshore Earthquakes". NOAA. Retrieved 23 June 2013. Italic or bold markup not allowed in: |publisher= (help)
  18. ^ Dziak, Robert P.; Fox, Christopher G. (1 December 1999). "The January 1998 Earthquake swarm at Axial Volcano, Juan de Fuca Ridge: Hydroacoustic evidence of seafloor volcanic activity". Geophysical Research Letters. 26 (23): 3429–3432. Bibcode:1999GeoRL..26.3429D. doi:10.1029/1999gl002332.
  19. ^ Floyd, Mark (26 October 2009). "OSU researchers find cause of 2008 offshore earthquake swarms". Corvallis Gazette Times. Retrieved 26 June 2013.
  20. ^ Lay, Thorne; Okal, Emile (1983). "The Gilbert Islands (Republic of Kiribati) earthquake swarm of 1981–1983" (PDF). Physics of the Earth and Planetary Interiors. 33 (4): 284–303. Bibcode:1983PEPI...33..284L. doi:10.1016/0031-9201(83)90046-8.
  21. ^ Wetmiller, Robert J. (December 1971). "An earthquake swarm on the Queen Charlotte Islands Fracture Zone". Bulletin of the Seismological Society of America. 61 (6): 1489–1505.
Amurian Plate

The Amurian Plate (or Amur Plate; also occasionally referred to as the China Plate) is a minor tectonic plate in the northern and eastern hemispheres. It covers Manchuria, the Korean Peninsula, the Yellow Sea, and Primorsky Krai. Once thought to be a part of the Eurasian Plate, the Amur Plate is now generally considered to be a separate plate moving southeast with respect to the Eurasian Plate.

The Amurian Plate is named after the Amur River, that forms the border between the Russian Far East and Northeastern China.

It is bounded on the north, west, and southwest by the Eurasian Plate, on the east by the Okhotsk Plate, to the southeast by the Philippine Sea Plate along the Suruga Trough and the Nankai Trough, and the Okinawa Plate, and the Yangtze Plate.The Baikal Rift Zone is considered a boundary between the Amurian Plate and the Eurasian Plate. GPS measurements indicate that the plate is slowly rotating counterclockwise.

The Amurian Plate may have been involved in the 1976 Tangshan earthquake in China.

Balmoral Reef Plate

The Balmoral Reef Plate is a small tectonic plate (microplate) located in the south Pacific north of Fiji. Clockwise from the north, it borders the Pacific Plate, Australian Plate, Conway Reef Plate, and the New Hebrides Plate. The northern and western borders are a divergent boundary while the rest of the borders are transform and convergent boundaries. The Balmoral Reef Plate's ocean crust is less than 12 million years old and is spreading between the New Hebrides and Tonga subduction.

Cocos Plate

The Cocos Plate is a young oceanic tectonic plate beneath the Pacific Ocean off the west coast of Central America, named for Cocos Island, which rides upon it. The Cocos Plate was created approximately 23 million years ago when the Farallon Plate broke into two pieces, which also created the Nazca Plate. The Cocos Plate also broke into two pieces, creating the small Rivera Plate. The Cocos Plate is bounded by several different plates. To the northeast it is bounded by the North American Plate and the Caribbean Plate. To the west it is bounded by the Pacific Plate and to the south by the Nazca Plate.

Conway Reef Plate

The Conway Reef Plate is a small tectonic plate (microplate) located in the south Pacific west of Fiji. It is bounded on the east and west by convergent boundaries, the western boundary is with the New Hebrides Plate while the eastern is with the Australian Plate. A short transform boundary also exists with the Balmoral Reef Plate.

Eurasian Plate

The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia. It also includes oceanic crust extending westward to the Mid-Atlantic Ridge and northward to the Gakkel Ridge.

The eastern side is a boundary with the North American Plate to the north and a boundary with the Philippine Sea Plate to the south and possibly with the Okhotsk Plate and the Amurian Plate. The southerly side is a boundary with the African Plate to the west, the Arabian Plate in the middle and the Indo-Australian Plate to the east. The westerly side is a divergent boundary with the North American Plate forming the northernmost part of the Mid-Atlantic Ridge, which is straddled by Iceland. All of the volcanic eruptions in Iceland, such as the 1973 eruption of Eldfell, the 1783 eruption of Laki, and the 2010 eruption of Eyjafjallajökull, are caused by the North American and the Eurasian Plates moving apart, which is a result of divergent plate boundary forces.

The geodynamics of central Asia is dominated by the interaction between the Eurasian and Indian Plates. In this area, many subplates or crust blocks have been recognized, which form the Central Asian and the East Asian transit zones.

Futuna Plate

The Futuna Plate is a very small tectonic plate located near the south Pacific island of Futuna. It is sandwiched between the Pacific Plate to the north and the Australian Plate to the south with the Niuafo'ou Plate to the east.

Indo-Australian Plate

The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters. It was formed by the fusion of Indian and Australian plates approximately 43 million years ago.

Kermadec Plate

The Kermadec Plate is a very long and narrow tectonic plate located west of the Kermadec Trench in the south Pacific Ocean. Also included on this tectonic plate is a small portion of the North Island of New Zealand and the Kermadec Islands. It is separated from the Australian Plate by a long divergent boundary which forms a back-arc basin. This area is highly prone to earthquakes and tsunami.

Manus Plate

The Manus Plate is a tiny tectonic plate located northeast of New Guinea. It is sandwiched between the North Bismarck Plate and the South Bismarck Plate.

Maoke Plate

The Maoke Plate is a small tectonic plate located in western New Guinea underlying the Sudirman Range from which the highest mountain on the island- Puncak Jaya rises. To its east is a convergent boundary with the Woodlark Plate. To the south lies a transform boundary with the Australian Plate and the Bird's Head Plate lies to the west.

New Hebrides Plate

The New Hebrides Plate, sometimes called the Neo-Hebridean Plate, is a minor tectonic plate located in the Pacific Ocean near the island nation of Vanuatu. The plate is bounded on the southwest by the Indo-Australian Plate which is subducting below it. The New Hebrides Subduction Zone is extremely active, producing over 20 earthquakes of magnitude 7 or higher in just the past 25 years.

Niuafo'ou Plate

The Niuafo'ou Plate is a small tectonic plate located west of the islands of Tonga. This plate is sandwiched between the Pacific Plate to the north, the very unstable Tonga Plate to the east and the Australian Plate to the west. It is primarily surrounded by convergent boundaries. This plate is riddled with active faults thus making the area extremely earthquake prone.

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76,000,000 km2 (29,000,000 sq mi), it is the Earth's second largest tectonic plate, behind the Pacific Plate (which borders the plate to the west).

It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust. The interior of the main continental landmass includes an extensive granitic core called a craton. Along most of the edges of this craton are fragments of crustal material called terranes, which are accreted to the craton by tectonic actions over a long span of time. It is thought that much of North America west of the Rocky Mountains is composed of such terranes.

North Bismarck Plate

The North Bismarck Plate is a small tectonic plate located in the Bismarck Sea off the northeast coast of New Guinea.

Okhotsk Plate

The Okhotsk Plate is a minor tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the North American Plate. The boundary is a left-lateral moving transform fault, the Ulakhan Fault. On the east, the plate is bounded by the Pacific Plate at the Kuril-Kamchatka Trench and the Japan Trench, on the south by the Philippine Sea Plate at the Nankai Trough, on the west by the Eurasian Plate, and possibly on the southwest by the Amurian Plate.

Pacific Plate

The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres (40,000,000 sq mi), it is the largest tectonic plate.The Pacific Plate contains an interior hot spot forming the Hawaiian Islands.Hillis and Müller are reported to consider the Bird's Head Plate to be moving in unison with the Pacific Plate. Bird considers them to be unconnected.

Solomon Sea Plate

The Solomon Sea Plate is a minor tectonic plate to the northwest of the Solomon Islands in the south Pacific Ocean, it roughly corresponds with the Solomon Sea east of Papua New Guinea.

South Bismarck Plate

The South Bismarck Plate is a small tectonic plate located in the southern Bismarck Sea. The eastern part of New Guinea and the island of New Britain are on this plate.

Timor Plate

The Timor Plate is a microplate in southeast Asia carrying the island of Timor and surrounding islands. The Australian Plate is subducting under the southern edge of the plate, while a small divergent boundary is located on the eastern edge. Another convergent boundary exists with the Banda Sea Plate to the north, and to the west is a transform boundary.

Woodlark Plate

The Woodlark Plate is a small tectonic plate located in the eastern half of the island of New Guinea. The Caroline plate subducts along its northern border while the Maoke Plate converges on the west, the Australian plate converges on the south, and on the east an undefined compressive zone which may be a transform fault marking the boundary with the adjoining Solomon Sea Plate.

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