Convergent boundary

A convergent boundary is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other causing a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Benioff Zone.[1] These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.

Plate tectonics is driven by convection cells in the mantle. Convection cells are the result of heat generated by radioactive decay of elements in the mantle escaping to the surface and the return of cool materials from the surface to the mantle.[2] These convection cells bring hot mantle material to the surface along spreading centers creating new crust. As this new crust is pushed away from the spreading center by the formation of newer crust, it cools, thins, and becomes denser. Subduction initiates when this dense crust converges with the less dense crust. The force of gravity helps drive the subducting slab into the mantle. Evidence supports that the force of gravity will increase plate velocity.[3] As the relatively cool subducting slab sinks deeper into the mantle, it is heated causing dehydration of hydrous minerals. This releases water into the hotter asthenosphere, which leads to partial melting of asthenosphere and volcanism. Both dehydration and partial melting occurs along the 1000 °C isotherm, generally at depths of 65 – 130  km.[4][5]

Some lithospheric plates consist of both continental and oceanic lithosphere. In some instances, initial convergence with another plate will destroy oceanic lithosphere, leading to convergence of two continental plates. Neither continental plate will subduct. It is likely that the plate may break along the boundary of continental and oceanic crust. Seismic tomography reveals pieces of lithosphere that have broken off during convergence.

Continental-continental destructive plate boundary
Simplified diagram of a convergent boundary

Subduction zones

Subduction zones are areas where one lithospheric plate slides beneath another at a convergent boundary due to lithospheric density differences. These plates dip at an average of 45° but can vary. Subduction zones are often marked by an abundance of earthquakes, the result of internal deformation of the plate, convergence with the opposing plate, and bending at the oceanic trench. Earthquakes have been detected to a depth of 670  km. The relatively cold and dense subducting plates are pulled into the mantle and help drive mantle convection.[6]

Oceanic – Oceanic Convergence

In collisions between two oceanic plates, the cooler, denser oceanic lithosphere sinks beneath the warmer, less dense oceanic lithosphere. As the slab sinks deeper into the mantle, it releases water from dehydration of hydrous minerals in the oceanic crust. This water reduces the melting temperature of rocks in the asthenosphere and causes partial melting. Partial melt will travel up through the asthenosphere, eventually, reach the surface, and form volcanic island arcs.

Continental – Oceanic Convergence

When oceanic lithosphere and continental lithosphere collide, the dense oceanic lithosphere subducts beneath the less dense continental lithosphere. An accretionary wedge forms on the continental crust as deep-sea sediments and oceanic crust are scraped from the oceanic plate. Volcanic arcs form on continental lithosphere as the result of partial melting due to dehydration of the hydrous minerals of the subducting slab.

Continental – Continental Convergence

Some lithospheric plates consist of both continental and oceanic crust. Subduction initiates as oceanic lithosphere slides beneath continental crust. As the oceanic lithosphere subducts to greater depths, the attached continental crust is pulled closer to the subduction zone. Once the continental lithosphere reaches the subduction zone, subduction processes are altered as continental lithosphere is more buoyant and resists subduction beneath other continental lithosphere. A small portion of the continental crust may be subducted until the slab breaks, allowing the oceanic lithosphere to continue subducting, hot asthenosphere to rise and fill the void, and rebound of the continental lithosphere.[7] Evidence of this continental rebound include ultrahigh pressure metamorphic rocks which form at depths of 90 – 125 km that are exposed at the surface.[8]

Volcanism and Volcanic Arcs

The oceanic crust contains hydrated minerals such as the amphibole group. During subduction, oceanic lithosphere is heated and metamorphosed causing dehydration of these hydrous minerals contained within basalts, releasing water into the asthenosphere. The release of water into the asthenosphere leads to partial melting. Partial melting allows the rise of more buoyant, hot material and can lead to volcanism at the surface and emplacement of plutons in the subsurface. These processes which generate magma are not entirely understood.

Where these magmas reach the surface they create volcanic arcs. Volcanic arcs can form as island arc chains or as arcs on continental crust. Three series of volcanic rocks generally form arcs, Tholeiitic (low iron basalts), calc-alkaline (moderately enriched in potassium and incompatible elements), and alkaline (highly enriched in potassium) which are very rare.[5]

Back arc basins

Back arc basins form behind a volcanic arc and are associated with extensional tectonics and high heat flow, often being home to seafloor spreading centers. These spreading centers are like mid ocean ridges, though the magma composition of back arc basins is generally more varied and contains a higher water content than mid ocean ridge magmas.[9] Back arc basins are often characterized by thin, hot lithosphere. Opening of back arc basins are still being studied but it is possible that movement of hot asthenosphere into lithosphere causes extension.[10]

Oceanic trenches

Oceanic trenches are narrow topographic lows that mark convergent boundaries or subduction zones. Oceanic trenches can be average 50 – 100  km wide and can be several thousand kilometers long. Oceanic trenches form as a result of bending of the subducting slab. Depth of oceanic trenches seems to be controlled by age of the oceanic lithosphere being subducted.[5] Sediment fill in oceanic trenches varies and generally depends on abundance of sediment input from surrounding areas. An oceanic trench, the Mariana Trench, is the deepest point of the ocean at a depth of approximately 11,000 m.

Earthquakes

Earthquakes are common along convergent boundaries. A region of high earthquake activity, the Benioff zone, generally dips 45° and marks the subducting plate. Earthquakes will occur to a depth of 670  km along the Benioff. Both compressional and extensional forces act along convergent boundaries. On the inner walls of trenches, compressional faulting or reverse faulting occurs due to the relative motion of the two plates. Reverse faulting scrapes off ocean sediment and leads to the formation of an accretionary wedge. Reverse faulting can lead to massive earthquakes, such as the magnitude 9.1 Sumatra earthquake of 2004.  Tensional or normal faulting occurs on the outer wall of the trench, likely due to bending of the down going slab.[11]

Accretionary Wedge

Accretionary wedges (also called accretionary prisms) form as sediment is scraped from the subducting lithosphere and emplaced against the overriding lithosphere. These sediments include igneous crust, turbidite sediments, and pelagic sediments. Imbricate thrust faulting along a basal decollement surface occurs in accretionary wedges as forces continue to compress and fault these newly added sediments.[5] The continued faulting of the accretionary wedge leads to overall thickening of the wedge.[12] Seafloor topography plays some role in accretion, especially emplacement of igneous crust.[13]

Convergent Boundaries and Natural Disasters

Some of the deadliest natural disasters have occurred due to convergent boundary processes. The 2004 Indian Ocean earthquake and tsunami was triggered by an earthquake along the convergent boundary of the Indian plate and Burma microplate and killed over 200,000 people.  The 2011 tsunami off the coast of Japan, which caused 16,000 deaths and did US$360 billion in damage, was caused by a magnitude 9 earthquake along the convergent boundary of the Eurasian plate and Pacific Plate.

Examples

See also

  • List of tectonic plates – A list of the relatively moving sections of the lithosphere of the Earth
  • List of tectonic plate interactions – Definitions and examples of the interactions between the relatively mobile sections of the lithosphere
  • Obduction – The overthrusting of oceanic lithosphere onto continental lithosphere at a convergent plate boundary

References

  1. ^ 1946–, Wicander, Reed (2013). Geol. Monroe, James S. (James Stewart), 1938– (2nd ed.). Belmont, CA: Cengage Wadsworth. ISBN 978-1133108696. OCLC 795757302.
  2. ^ Tackley, Paul J. (2000-06-16). "Mantle Convection and Plate Tectonics: Toward an Integrated Physical and Chemical Theory". Science. 288 (5473): 2002–2007. Bibcode:2000Sci...288.2002T. doi:10.1126/science.288.5473.2002. ISSN 1095-9203. PMID 10856206.
  3. ^ Conrad, Clinton P.; Lithgow‐Bertelloni, Carolina (2004-10-01). "The temporal evolution of plate driving forces: Importance of "slab suction" versus "slab pull" during the Cenozoic". Journal of Geophysical Research: Solid Earth. 109 (B10): B10407. Bibcode:2004JGRB..10910407C. doi:10.1029/2004JB002991. ISSN 2156-2202.
  4. ^ Bourdon, Bernard; Turner, Simon; Dosseto, Anthony (2003-06-01). "Dehydration and partial melting in subduction zones: Constraints from U-series disequilibria". Journal of Geophysical Research: Solid Earth. 108 (B6): 2291. Bibcode:2003JGRB..108.2291B. doi:10.1029/2002JB001839. ISSN 2156-2202.
  5. ^ a b c d P., Kearey (2009). Global tectonics. Klepeis, Keith A., Vine, F. J. (3rd ed.). Oxford: Wiley-Blackwell. ISBN 9781405107778. OCLC 132681514.
  6. ^ Widiyantoro, Sri; Hilst, Rob D. Van Der; Grand, Stephen P. (1997-12-01). "Global seismic tomography: A snapshot of convection in the earth". GSA Today. 7 (4). ISSN 1052-5173.
  7. ^ Condie, Kent C. (2016-01-01). "Crustal and Mantle Evolution". Earth as an Evolving Planetary System. Academic Press. pp. 147–199. doi:10.1016/b978-0-12-803689-1.00006-7. ISBN 9780128036891.
  8. ^ Ernst, W. G.; Maruyama, S.; Wallis, S. (1997-09-02). "Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust". Proceedings of the National Academy of Sciences of the United States of America. 94 (18): 9532–9537. Bibcode:1997PNAS...94.9532E. doi:10.1073/pnas.94.18.9532. ISSN 0027-8424. PMC 23212. PMID 11038569.
  9. ^ Taylor, Brian; Martinez, Fernando (March 2002). "Mantle wedge control on back-arc crustal accretion". Nature. 416 (6879): 417–420. Bibcode:2002Natur.416..417M. doi:10.1038/416417a. ISSN 1476-4687. PMID 11919628.
  10. ^ Tatsumi, Yoshiyuki; Otofuji, Yo-Ichiro; Matsuda, Takaaki; Nohda, Susumu (1989-09-10). "Opening of the Sea of Japan back-arc basin by asthenospheric injection". Tectonophysics. 166 (4): 317–329. Bibcode:1989Tectp.166..317T. doi:10.1016/0040-1951(89)90283-7. ISSN 0040-1951.
  11. ^ Oliver, J.; Sykes, L.; Isacks, B. (1969-06-01). "Seismology and the new global tectonics". Tectonophysics. 7 (5–6): 527–541. Bibcode:1969Tectp...7..527O. doi:10.1016/0040-1951(69)90024-9. ISSN 0040-1951.
  12. ^ Konstantinovskaia, Elena; Malavieille, Jacques (2005-02-01). "Erosion and exhumation in accretionary orogens: Experimental and geological approaches". Geochemistry, Geophysics, Geosystems. 6 (2): Q02006. Bibcode:2005GGG.....6.2006K. doi:10.1029/2004GC000794. ISSN 1525-2027.
  13. ^ Sharman, George F.; Karig, Daniel E. (1975-03-01). "Subduction and Accretion in Trenches". GSA Bulletin. 86 (3): 377–389. Bibcode:1975GSAB...86..377K. doi:10.1130/0016-7606(1975)86<377:SAAIT>2.0.CO;2. ISSN 0016-7606.
Anatolian Plate

The Anatolian Plate or the Turkish Plate is a continental tectonic plate comprising most of the Anatolia (Asia Minor) peninsula (and the country of Turkey).

To the east, the East Anatolian Fault, a left lateral transform fault, forms a boundary with the Arabian Plate. To the south and southwest is a convergent boundary with the African Plate. This convergence manifests in compressive features within the oceanic crust beneath the Mediterranean as well as within the continental crust of Anatolia itself, and also by what are generally considered to be subduction zones along the Hellenic and Cyprus arcs.

The northern edge is a transform boundary with the Eurasian Plate, forming the North Anatolian Fault Zone (NAFZ).

Research indicates that the Anatolian Plate is rotating counterclockwise as it is being pushed west by the Arabian Plate, impeded from any northerly movement by the Eurasian Plate. In some references, the Anatolian Plate is referred to as a "block" of continental crust still coupled to the Eurasian Plate. But studies of the North Anatolian Fault indicate that Anatolia is de-coupled from the Eurasian Plate. It is now being squeezed by the Arabian Plate from the east and forced toward the west as the Eurasian Plate to its north is blocking motion in that direction. The African Plate is subducting beneath the Anatolian Plate along the Cyprus and Hellenic Arcs offshore in the Mediterranean Sea.

Awatere Fault

The Awatere Fault is an active dextral (right lateral) strike-slip fault in the northeastern part of South Island, New Zealand. It forms part of the Marlborough Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate, from the transform Alpine Fault to the Hikurangi Trench subduction zone.

The 1848 Marlborough earthquake was caused by rupture of the whole of the eastern section of the Awatere Fault.

Banda Sea Plate

The Banda Sea Plate is a minor tectonic plate underlying the Banda Sea in southeast Asia. This plate also carries a portion of Sulawesi Island, the entire Seram Island, and the Banda Islands. Clockwise from the east it is bounded by the Bird's Head Plate of western New Guinea, Australian Plate, Timor Plate, Sunda Plate, and the Molucca Sea Collision Zone.

The western border is a convergent boundary largely responsible for the mountains in western Sulawesi, subduction zones also exist on the eastern border near Seram and the southern border with the Timor Plate. A small rift is located in the middle of Sulawesi. It is a very seismically active area home to many volcanoes and the site of many large earthquakes, the largest of which was the 1938 Banda Sea earthquake which measured around 8.4 on the moment magnitude scale.

Bird's Head Plate

The Bird's Head Plate is a minor tectonic plate incorporating the Bird's Head Peninsula, at the western end of the island of New Guinea. Hillis and Müller consider it to be moving in unison with the Pacific Plate. Bird considers it to be unconnected to the Pacific Plate.The plate is separating from the Australian Plate and the small Maoke Plate along a divergent boundary to the southeast. Convergent boundaries exist along the north, between the Bird's Head and the Caroline Plate, the Philippine Sea Plate and the Halmahera Plate to the northwest. A transform boundary exists between the Bird's Head and the Molucca Sea Collision Zone to the southwest. Another convergent boundary exists between the Bird's Head and the Banda Sea Plate to the south.

Caroline Plate

The Caroline Plate is a minor tectonic plate that straddles the Equator in the eastern hemisphere located north of New Guinea. It forms a subduction zone along the border with the Bird's Head Plate and the Woodlark Plate to the south. A transform boundary forms the northern border with the Pacific Plate. Along the border with the Philippine Sea Plate is a convergent boundary that transitions into a rift.

The Caroline Plate was first proposed as a distinct plate by Weissel & Anderson 1978.

Clarence Fault

The Clarence Fault is an active dextral (right lateral) strike-slip fault in the northeastern part of South Island, New Zealand. It forms part of the Marlborough Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate, from the transform Alpine Fault to the Hikurangi Trench subduction zone.

Convergent

Convergent is an adjective for things that converge. It is commonly used in mathematics and may refer to:

Convergent boundary, a type of plate tectonic boundary

Convergent (continued fraction)

Convergent evolution

Convergent seriesConvergent may also refer to:

Convergent Books, an imprint of Crown Publishing Group

Convergent Technologies, a computer company

Gorda Plate

The Gorda Plate, located beneath the Pacific Ocean off the coast of northern California, is one of the northern remnants of the Farallon Plate. It is sometimes referred to (by, for example, publications from the USGS Earthquake Hazards Program) as simply the southernmost portion of the neighboring Juan de Fuca Plate, another Farallon remnant.

Unlike most tectonic plates, the Gorda Plate experiences significant intraplate deformation inside its boundaries. Numerous faults have been mapped in both the sediments and basement of the Gorda Basin, which is in the interior of the plate south of 41.6°N. Stresses from the neighboring North American Plate and Pacific Plate cause frequent earthquakes in the interior of the plate, including the 1980 Eureka earthquake (also known as the Gorda Basin event).The easterly side is a convergent boundary subducting under the North American Plate in northern California. The southerly side is a transform boundary with the Pacific Plate along the Mendocino Fault. The westerly side is a divergent boundary with the Pacific Plate forming the Gorda Ridge. This ridge provides morphological evidence of differing spreading rates, with the northern portion of the ridge being narrow, and the southern portion being wide. The northerly side is a transform boundary with the Juan de Fuca Plate, the Blanco Fracture Zone.

The subducting Gorda Plate is connected with the volcanoes in northern California, namely, Mount Shasta and Lassen Peak. Lassen Peak last erupted in 1914–1917.

IBM (disambiguation)

IBM is International Business Machines, an American multinational technology and consulting corporation, with headquarters in Armonk, New York.

IBM may also refer to:

IBM (atoms), a demonstration of the creation of the initials "IBM" using individual atoms in 1990

Inclusion body myositis, an inflammatory muscle disease

Injection blow molding, blow molding manufacturing process

Interacting boson model, in nuclear physics

International Brotherhood of Magicians

itty bitty machine company, or "ibm", a small computer retail store in Evanston, Illinois, United States

Izu–Bonin–Mariana Arc system, a plate tectonic convergent boundary in the Pacific Ocean

Invisible Black Matter, a fictional substance in Ajin: Demi-Human

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.

Mariana Plate

The Mariana Plate is a micro tectonic plate located west of the Mariana Trench which forms the basement of the Mariana Islands which form part of the Izu-Bonin-Mariana Arc. It is separated from the Philippine Sea Plate to the west by a divergent boundary with numerous transform fault offsets. The boundary between the Mariana and the Pacific Plate to the east is a subduction zone with the Pacific Plate subducting beneath the Mariana. This eastern subduction is divided into the Mariana Trench, which forms the southeastern boundary, and the Izu-Ogasawara Trench the northeastern boundary. The subduction plate motion is responsible for the shape of the Mariana plate and back arc.

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.

South American Plate

The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-Atlantic Ridge.

The easterly edge is a divergent boundary with the African Plate; the southerly edge is a complex boundary with the Antarctic Plate, the Scotia Plate, and the Sandwich Plate; the westerly edge is a convergent boundary with the subducting Nazca Plate; and the northerly edge is a boundary with the Caribbean Plate and the oceanic crust of the North American Plate. At the Chile Triple Junction, near the west coast of the Taitao–Tres Montes Peninsula, an oceanic ridge known as the Chile Rise is actively subducting under the South American Plate.

Geological research suggests that the South American Plate is moving westward away from the Mid-Atlantic Ridge: "Parts of the plate boundaries consisting of alternations of relatively short transform fault and spreading ridge segments are represented by a boundary following the general trend." As a result, the eastward-moving and more dense Nazca Plate is subducting under the western edge of the South American Plate, along the continent's Pacific coast, at a rate of 77 mm (3.0 in) per year. The collision of these two plates is responsible for lifting the massive Andes Mountains and for creating the numerous volcanoes which are strewn throughout them.

Sunda Arc

The Sunda Arc is a volcanic arc that produced the islands of Sumatra and Java, the Sunda Strait and the Lesser Sunda Islands. A chain of volcanoes forms the topographic spine of these islands.

The Sunda Arc marks an active convergent boundary between the East Eurasian plates that underlie Indonesia, especially the Sunda Plate and the Burma Plate, with the India and Australian Plates that form the seabed of the Indian Ocean and the Bay of Bengal. The Sunda Arc is a classic example of a volcanic island arc, in which all the elements of such geodynamic features can be identified.

The India and Australian Plates are subducting beneath the Sunda and Burma plates along the Sunda Arc. The tectonic deformation along this subduction zone in the Java Trench (also known as the Sunda Trench) caused the 2004 Indian Ocean earthquake of 26 December, 2004.

Thin-skinned deformation

Thin-skinned deformation is a style of deformation in plate tectonics at a convergent boundary which occurs with shallow thrust faults that only involves cover rocks (typically sedimentary rocks), and not deeper basement rocks.The thin-skinned style of deformation is typical of many fold and thrust belts developed in the foreland of a collisional zone or back arc of a continental volcanic arc. This is particularly the case where a good basal decollement exists, usually in a weaker layer like a shale, evaporite, or a zone of high pore fluid pressure. This was first described in Rocky Mountains of the United States, as part of the Sevier Orogeny.

In the rock record, this will increase the influence of more surficial rocks, which usually includes sedimentary rocks. Typically, you will see repeated sections of the same rock over and over as thrust faults, coming up from the decollement, stack the same layer on top of itself. The sediments that are created by this type of deformation are typically lithic sandstones.

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.

Wairarapa Fault

The Wairarapa Fault is an active seismic fault in the southern part of the North Island of New Zealand. It is a dextral (right lateral) strike-slip fault with a component of uplift to the northwest as expressed by the Rimutaka Range. It forms part of the North Island Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate.

Wairau Fault

The Wairau Fault is an active dextral (right lateral) strike-slip fault in the northeastern part of South Island, New Zealand. It forms part of the Marlborough Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate, from the transform Alpine Fault to the Hikurangi Trench subduction zone.

Wellington Fault

The Wellington Fault is an active seismic fault in the southern part of the North Island of New Zealand. It is a dextral (right-lateral) strike-slip fault with variable amounts of vertical movement causing uplift to the northwest, as expressed by a series of ranges. It forms part of the North Island Fault System, which accommodates the transfer of displacement along the oblique convergent boundary between the Indo-Australian Plate and Pacific Plate.

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