Map of Earth's 16 principal tectonic plates Divergent:
Spreading center
Extension zone
Convergent:
Subduction zone
Collision zone
Transform:
Dextral transform
Sinistral transform
Plate tectonics (from the Late Latin: tectonicus, from the Ancient Greek: τεκτονικός, lit.'pertaining to building') is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.
Earth's lithosphere, the rigid outer shell of the planet including the crust and upper mantle, is fractured into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". Where the plates meet, their relative motion determines the type of plate boundary (or fault): convergent, divergent, or transform. The relative movement of the plates typically ranges from zero to 10cm annually. Faults tend to be geologically active, experiencing earthquakes, volcanic activity, mountain-building, and oceanic trench formation.
Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Along convergent plate boundaries, the process of subduction carries the edge of one plate down under the other plate and into the mantle. This process reduces the total surface area (crust) of the Earth. The lost surface is balanced by the formation of new oceanic crust along divergent margins by seafloor spreading, keeping the total surface area constant in a tectonic "conveyor belt".
Tectonic plates are relatively rigid and float across the ductile asthenosphere beneath. Lateral density variations in the mantle result in convection currents, the slow creeping motion of Earth's solid mantle. At a seafloor spreading ridge, plates move away from the ridge, which is a topographic high, and the newly formed crust cools as it moves away, increasing its density and contributing to the motion. At a subduction zone the relatively cold, dense oceanic crust sinks down into the mantle, forming the downward convecting limb of a mantle cell, which is the strongest driver of plate motion. The relative importance and interaction of other proposed factors such as active convection, upwelling inside the mantle, and tidal drag of the Moon is still the subject of debate. (Full article...)
General concepts
Asthenosphere– Highly viscous, mechanically weak, and ductile region of Earth's mantle
Aulacogen– Failed arm of a triple junction, an inactive rift zone
Back-arc basin– Submarine features associated with island arcs and subduction zones
Bimodal volcanism– Eruption of both mafic and felsic lavas from a single volcanic centre
Continent– Large geographical region identified by convention
Crust– Outermost solid shell of astronomical bodies
Epeirogenic movement– Upheavals or depressions of land exhibiting long wavelengths and little folding
Fault (geology)– Fracture or discontinuity in rock across which there has been displacement
Fault mechanics– Field of study that investigates the behavior of geologic faults
Active fault– Geological fault likely to be the source of an earthquake sometime in the future
Flux melting– The process by which the melting point is reduced by the admixture of a material known as a flux
Appalachia (Mesozoic)– Mesozoic land mass separated from Laramidia to the west by the Western Interior SeawayPages displaying short descriptions of redirect targets
Goiás Ocean– Major shear zone that developed in the PrecambrianPages displaying short descriptions of redirect targets
Hudson Seaway– Major seaway of North America during the Cretaceous Period
Iapetus Ocean– Ocean that existed in the late Neoproterozoic and early Paleozoic eras
Khanty Ocean– Small Precambrian ocean between Baltica and the Siberian continent
Lapland-Kola Ocean– Zone of granulite rock in the Cap of the North in Norway, Finland and Murmansk Oblast in RussiaPages displaying short descriptions of redirect targets
Mirovia– Hypothesized superocean surrounding the supercontinent Rodinia in the Neoproterozoic Era
Paleo-Tethys Ocean– Ocean on the margin of Gondwana between the Middle Cambrian and Late Triassic
Pan-African Ocean– Hypothesized paleo-ocean whose closure created the supercontinent of Pannotia
Pannonian Sea– Shallow ancient sea where the Pannonian Basin in Central Europe is today
Panthalassa– Prehistoric superocean that surrounded Pangaea
Paratethys– Prehistoric shallow inland sea in Eurasia
Pharusian Ocean– Ancient ocean that existed from 800 to 635 million years ago
Piemont-Liguria Ocean– Former piece of oceanic crust that is seen as part of the Tethys Ocean
Poseidon Ocean– Supposed ocean that existed in the Mesoproterozoic period
Pre-Svecofennian Ocean– Geological process that resulted in formation of continental crust in Sweden, Finland and RussiaPages displaying short descriptions of redirect targets
Proto-Tethys Ocean– Ancient ocean that existed from the latest Ediacaran to the Carboniferous
Rheic Ocean– Ancient ocean which separated two major palaeocontinents, Gondwana and Laurussia
Slide Mountain Ocean– An ancient ocean that existed between the Intermontane Islands and North America
Sundance Sea– Inland sea that existed in North America during the mid-to-late Jurassic Period of the Mesozoic Era
Tethys Ocean– Prehistoric ocean between Gondwana and Laurasia
Tornquist Sea– Sea between the palaeocontinents Avalonia and Baltica about 600 to 450 million years ago
Turgai Sea– Large shallow body of salt water of the Mesozoic and Cenozoic ErasPages displaying short descriptions of redirect targets
Ural Ocean– Small, ancient ocean between Siberia and Baltica
Valais Ocean– Subducted ocean basin. Remnants found in the Alps in the North Penninic nappes.
Western Interior Seaway– Large prehistoric inland sea that split the continent of North America
Benue Trough– Major geological structure underlying a large part of Nigeria
Central Lowlands– Geologically defined area of relatively low-lying land in southern Scotland
Eastern North America Rift Basins– Assemblage of Upper Triassic and Lower Jurassic sedimentary rocksPages displaying short descriptions of redirect targets
Fundy Basin– Sediment-filled rift basin on the Atlantic coast of southeastern Canada
Gulf of Suez Rift– Continental rift zone that was active between the Late Oligocene and the end of the Miocene
Gulf St Vincent– South Australian southern coast water inlet bordered by the Yorke and Fleurieu Peninsulas
Armorican Massif– Geologic massif that covers a large area in the northwest of France
Armorican terrane– Microcontinent or group of continental fragments rifted away from Gondwana
Avalonia– Microcontinent in the Paleozoic era named for the Avalon Peninsula in Newfoundland
Briançonnais zone– Piece of continental crust in the Penninic nappes of the Alps
Bronson Hill Arc– Bimodal volcanic arc and associated Ordovician sediments
Buffalo Head Terrane– Terrane in the western Canadian Shield in northern Alberta
Cache Creek Terrane– Geologic terrane in British Columbia and southern Yukon, Canada
Carolina terrane– Exotic terrane from central Georgia to central Virginia in the United States
Cassiar Terrane– Cretaceous terrane located in the Northern Interior of British Columbia and southern Yukon
Chilenia– Ancient microcontinent, containing central Chile and western Argentina
Chiloé Block– Ancient microcontinent or terrane that collided with the South American Plate during the Proterozoic
Cuyania– Ancient microcontinent now part of Argentina
Cymru Terrane– Inferred fault bounded terrane of the basement rocks of the southern United Kingdom
Florida Platform– Flat geological feature with the emergent portion forming the Florida peninsula
Franciscan Assemblage– Late Mesozoic terrane of heterogeneous rocks in the California Coast RangesPages displaying short descriptions of redirect targets
Ganderia– Terrane in the northern Appalachians which broke off the supercontinent Gondwana
Gascoyne Complex– Granite and metamorphic rock in Western Australia
Plate tectonics is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates which have been slowly moving since about 3.4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s.
Orogeny is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An orogenic belt or orogen develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involves a series of geological processes collectively called orogenesis. These include both structural deformation of existing continental crust and the creation of new continental crust through volcanism. Magma rising in the orogen carries less dense material upwards while leaving more dense material behind, resulting in compositional differentiation of Earth's lithosphere. A synorogenic process or event is one that occurs during an orogeny.
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subduction zone. A transform fault is a special case of a strike-slip fault that also forms a plate boundary.
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts, which eventually become rift valleys. Most active divergent plate boundaries occur between oceanic plates and exist as mid-oceanic ridges.
The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76 million km2 (29 million sq mi), it is the Earth's second largest tectonic plate, behind the Pacific 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 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 centre of the triple junction during the Early Jurassic. It is named for the Farallon Islands, which are located just west of San Francisco, California.
The African Plate, also known as the Nubian Plate, is a major tectonic plate that includes much of the continent of Africa and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate to the west ; the Arabian Plate and Somali Plate to the east; the Eurasian Plate, Aegean Sea Plate and Anatolian Plate to the north; and the Antarctic Plate to the south.
The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of the Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of erosion and weathering worked to tear them down. Even after many millions of years, records of Earth's great upheavals remain imprinted as textural variations and surface patterns that define distinctive landscapes or provinces.
Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals. Changes in seismic wave velocities have shown that at a certain depth, there is a reasonably sharp contrast between the more felsic upper continental crust and the lower continental crust, which is more mafic in character.
Arctica, or Arctida was an ancient continent which formed approximately 2.565 billion years ago in the Neoarchean era. It was made of Archaean cratons, including the Siberian Craton, with its Anabar/Aldan shields in Siberia, and the Slave, Wyoming, Superior, and North Atlantic cratons in North America. Arctica was named by Rogers 1996 because the Arctic Ocean formed by the separation of the North American and Siberian cratons. Russian geologists writing in English call the continent "Arctida" since it was given that name in 1987, alternatively the Hyperborean craton, in reference to the hyperboreans in Greek mythology.
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about 2,600 meters (8,500 ft) and rises about 2,000 meters (6,600 ft) above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin.
The Paleo-Tethys or Palaeo-Tethys Ocean was an ocean located along the northern margin of the paleocontinent Gondwana that started to open during the Middle Cambrian, grew throughout the Paleozoic, and finally closed during the Late Triassic; existing for about 400 million years.
The North China Craton is a continental crustal block with one of Earth's most complete and complex records of igneous, sedimentary and metamorphic processes. It is located in northeast China, Inner Mongolia, the Yellow Sea, and North Korea. The term craton designates this as a piece of continent that is stable, buoyant and rigid. Basic properties of the cratonic crust include being thick, relatively cold when compared to other regions, and low density. The North China Craton is an ancient craton, which experienced a long period of stability and fitted the definition of a craton well. However, the North China Craton later experienced destruction of some of its deeper parts (decratonization), which means that this piece of continent is no longer as stable.
The Trans-Hudson orogeny or Trans-Hudsonian orogeny was the major mountain building event (orogeny) that formed the Precambrian Canadian Shield and the North American Craton, forging the initial North American continent. It gave rise to the Trans-Hudson orogen (THO), or Trans-Hudson Orogen Transect (THOT), which is the largest Paleoproterozoic orogenic belt in the world. It consists of a network of belts that were formed by Proterozoic crustal accretion and the collision of pre-existing Archean continents. The event occurred 2.0–1.8 billion years ago.
The Wopmay orogen is a Paleoproterozoic orogenic belt in northern Canada which formed during the collision between the Hottah terrane, a continental magmatic arc, and the Archean Slave Craton at about 1.88 Ga. The collision lead to the short-lived Calderian orogeny. The formation was named for Wilfrid Reid "Wop" May, OBE, DFC, a Canadian flying ace in the First World War and a leading post-war aviator.
Patagonia comprises the southernmost region of South America, portions of which lie on either side of the Argentina-Chile border. It has traditionally been described as the region south of the Rio Colorado, although the physiographic border has more recently been moved southward to the Huincul fault. The region's geologic border to the north is composed of the Rio de la Plata craton and several accreted terranes comprising the La Pampa province. The underlying basement rocks of the Patagonian region can be subdivided into two large massifs: the North Patagonian Massif and the Deseado Massif. These massifs are surrounded by sedimentary basins formed in the Mesozoic that underwent subsequent deformation during the Andean orogeny. Patagonia is known for its vast earthquakes and the damage they cause.
The South China Craton or South China Block is one of the Precambrian continental blocks in China. It is traditionally divided into the Yangtze Block in the NW and the Cathaysia Block in the SE. The Jiangshan–Shaoxing Fault represents the suture boundary between the two sub-blocks. Recent study suggests that the South China Block possibly has one more sub-block which is named the Tolo Terrane. The oldest rocks in the South China Block occur within the Kongling Complex, which yields zircon U–Pb ages of 3.3–2.9 Ga.
The plate theory is a model of volcanism that attributes all volcanic activity on Earth, even that which appears superficially to be anomalous, to the operation of plate tectonics. According to the plate theory, the principal cause of volcanism is extension of the lithosphere. Extension of the lithosphere is a function of the lithospheric stress field. The global distribution of volcanic activity at a given time reflects the contemporaneous lithospheric stress field, and changes in the spatial and temporal distribution of volcanoes reflect changes in the stress field. The main factors governing the evolution of the stress field are:
Changes in the configuration of plate boundaries.
Vertical motions.
Thermal contraction.
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