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 10 cm 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
Superoceans
Superocean – Ocean that surrounds a supercontinent
Mirovia – Hypothesized superocean surrounding the supercontinent Rodinia in the Neoproterozoic Era
Pan-African Ocean – Hypothesized paleo-ocean whose closure created the supercontinent of Pannotia
Panthalassa – Prehistoric superocean that surrounded Pangaea
Laptev Sea Rift – Divergent tectonic plate boundary between the North American Plate and the Eurasian Plate
Afar Triangle – Geological depression caused by the Afar Triple Junction
Oceanic ridges
Aden Ridge – Part of an active oblique rift system in the Gulf of Aden, between Somalia and the Arabian Peninsula
Cocos Ridge – Pacific volcanic hotspotPages displaying short descriptions of redirect targets
Explorer Ridge – Mid-ocean ridge west of British Columbia, Canada
Gorda Ridge – Tectonic spreading center off the northern coast of California and southern Oregon
Juan de Fuca Ridge – Divergent plate boundary off the coast of the Pacific Northwest region of North America
South American–Antarctic Ridge – Mid-ocean ridge in the South Atlantic between the South American Plate and the Antarctic Plate
Chile Rise – Submarine oceanic ridge in the Pacific OceanPages displaying short descriptions of redirect targets
East Pacific Rise – A mid-oceanic ridge at a divergent tectonic plate boundary on the floor of the Pacific Ocean
East Scotia Ridge – Minor oceanic tectonic plate between the Antarctic and South American platesPages displaying short descriptions of redirect targets
Gakkel Ridge – Mid-oceanic ridge under the Arctic Ocean between the North American Plate and the Eurasian Plate(Mid-Arctic Ridge)
Nazca Ridge – Submarine ridge off the coast of Peru
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
Anatolian Plate – Continental tectonic plate comprising most of the Anatolia (Asia Minor) peninsulaPages displaying short descriptions of redirect targets
Antarctic Plate – Major tectonic plate containing Antarctica and the surrounding ocean floor
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
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