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 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".
While Earth is the only planet known to currently have active plate tectonics, evidence suggests that other planets and moons have experienced or exhibit forms of tectonic activity. For example, Jupiter's moon Europa shows signs of ice crustal plates moving and interacting, similar to Earth's plate tectonics. Additionally, Mars and Venus are thought to have had past tectonic activity, though not in the same form as Earth.
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, ductile, and mechanically weak 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 displaced rock
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 – 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 – Geology of Norway, Finland and 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 – Ancient ocean between the Intermontane Islands and North America
Chile Rise – Submarine oceanic ridge in the Pacific OceanPages displaying short descriptions of redirect targets
East Pacific Rise – 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(Mid-Arctic Ridge)
Nazca Ridge – Submarine ridge off the coast of Peru
Pacific-Antarctic Ridge – Tectonic plate boundary in the South Pacific OceanPages displaying short descriptions of redirect targets
Central Indian Ridge – North-south-trending mid-ocean ridge in the western Indian Ocean
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
Kula-Farallon Ridge – Ancient mid-ocean ridgePages displaying short descriptions of redirect targets
Anatolian plate – Continental tectonic plate comprising most of the Anatolian Peninsula (Asia Minor)Pages displaying short descriptions of redirect targets
Antarctic plate – Major tectonic plate containing Antarctica and the surrounding ocean floor
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
Aden-Owen-Carlsberg triple junction – Junction of three tectonic plates in the northwest Indian OceanPages displaying short descriptions of redirect targets
Galapagos triple junction – Place where the boundaries of the Cocos plate, the Nazca plate, and the Pacific plate meetPages displaying short descriptions of redirect targets
Kamchatka-Aleutian triple junction – Place where the Pacific plate, the Okhotsk plate, and the North American plate meetPages displaying short descriptions of redirect targets
Karlıova triple junction – Place where the Anatolian plate, the Eurasian plate and the Arabian plate meet
Macquarie triple junction – Place where the Indo-Australian plate, Pacific plate, and Antarctic plate meet
Mendocino triple junction – Point where the Gorda plate, the North American plate, and the Pacific plate meet