Basement rock usually refers to the thick foundation of ancient, and oldest metamorphic and igneous rock that forms the crust of continents, often in the form of granite. Basement rock is contrasted to overlying sedimentary rocks which are laid down on top of the basement rocks after the continent was formed, such as sandstone and limestone. The sedimentary rocks which may be deposited on top of the basement usually form a relatively thin veneer, but can be more than 3 miles thick. The basement rock of the crust can be 20-30 miles thick, or more. The basement rock can be located under layers of sedimentary rock, or be visible at the surface. Basement rock is visible at the bottom of the Grand Canyon, consisting of 1.7-2 billion year old granite and schist, the Vishnu schist and Zoroaster granite. The vishnu schist is believed to be highly metamorphosed igneous rocks and shale, from basalt, mud and clay laid from volcanic eruptions, and the granite is the result of magma intrusions into the vishnu schist. An extensive cross section of sedimentary rocks laid down on top of it through the ages is visible as well. The term Metamorphic can be associated with a number of meanings:- Metamorphic rock The term for rocks that have been transformed by extreme heat and pressure. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks form when rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Earth cutaway from core to exosphere. ... Animated, colour-coded map showing the various continents. ... Close-up of granite from Yosemite National Park, valley of the Merced River Quarrying granite for the Mormon Temple, Utah Territory. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Red sandstone interior of Lower Antelope Canyon, Arizona, worn smooth due to erosion by flash flooding over millions of years Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. ... -1... Christmas Day 2006, South Rim The Grand Canyon is a very colorful, steep-sided gorge, carved by the Colorado River in the U.S. state of Arizona. ... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Shale Shale is a fine-grained sedimentary rock whose original constituents were clays or muds. ... Basalt Basalt (IPA: ) is a common gray to black extrusive volcanic rock. ... In computer gaming, a MUD (Multi-User Dungeon, Domain or Dimension) is a multi-player computer game that combines elements of role-playing games, hack and slash style computer games and social chat rooms. ... The Gay Head cliffs in Marthas Vineyard are made almost entirely of clay. ...

The thickest crust on the planet can be found in the Tibetan Plateau where the Indian subcontinent is colliding with Asia and China to the north, causing the formation of the Himalayas, the tallest mountains in the world. The crust there is said to be 70 miles thick. Tibet Autonomous Region, Qinghai Province and Sichuan Province of China lie on the Tibetan Plateau. ... Map of South Asia (see note) This article deals with the geophysical region in Asia. ... World map showing the location of Asia. ... Himalaya, see Himalaya (film). ... Lyskamm, 4 527 m, Pennine Alps A mountain is a landform that extends above the surrounding terrain in a limited area. ...

The basement rocks of the continental crust tend to be much older than the oceanic crust. The oceanic crust can be from 0-250 million years in age, and is usually thinner (10 miles or so) and composed of basaltic rocks. Continental crust is older due to the fact that continental crust is light and thick enough so it is not subducted, while oceanic crust is periodically subducted and replaced at subduction and oceanic rifting areas. Basalt Basalt (IPA: ) is a common gray to black extrusive volcanic rock. ... The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone. ... In geology, a rift is a place where the Earths lithosphere is expanding. ...

The basement rocks are often highly metamorphosed and complex. They may consist of many different types of rock - volcanic, intrusive igneous and metamorphic. They may also contain fragments of oceanic crust that became wedged between plates when a terrane was accreted to the edge of the continent. Any of this material may be folded, refolded and metamorphosed. New igneous rock may freshly intrude into the crust from underneath, or may form underplating, where the new igneous rock forms a layer on the underside of the crust. It is said that the majority of continental crust on the planet is around 1-3 billion years old, and it is theorised that there was at least one period of rapid expansion and accretion to the continents during the Precambrian. Age of oceanic crust Oceanic crust is the part of Earths lithosphere which underlies the ocean basins. ... A terrane in paleogeography is an accretion that has collided with a continental nucleus, or craton but can be recognized by the foreign origin of its rock strata. ...

Much of the basement rock may have originally been oceanic crust, but it was highly metamorphosed and converted into continental crust via a series of events. A typical pattern is as follows. It is possible for oceanic crust to be subducted down into the Earth's mantle, at subduction fronts, where oceanic crust is being pushed down into the mantle by an overridding plate of oceanic or continental crust. The thickness of the Earths crust (km). ... Earth cutaway from core to exosphere. ...

When a plate of oceanic crust is subducted beneath an overriding plate of oceanic crust, as the underthrusting crust melts, it can cause upwelling of magma that can cause volcanism along the subduction front on the overridding plate. This produces an oceanic chain of volcanoes, like Japan. This volcanism causes metamorphosis of rocks, intrusions of magma that produce rocks such as granite, and thickens the crust by depositing additional layers of rock from volcanoes. This tends to make the crust lighter and thicker, as a result making it immune to subduction. This article is about volcanoes in geology. ... For other uses, see Volcano (disambiguation). ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... This balancing rock, Steamboat Rock stands in Garden of the Gods park in Colorado Springs, CO The rocky side of a mountain creek near Orosí, Costa Rica. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ...

Oceanic crust can be subducted, while continental crust cannot. Eventually, the subduction of the underthrusting oceanic crust can bring the volcano chain close to a continent, and collide with it. When the overriding plate collides with the continent, instead of being subducted, it is accreted to the edge of the continent and becomes a part of that continent. Thin strips or fragments of the underthrusting plate may also remain attached to the edge of the continent causing those fragments of oceanic crust to be wedged and tilted between the converging plates. In this manner, continents can grow over time as new terranes are accreted to their edges, and so continents can be composed of a complex quilt of terranes of varying ages. Oceanic-continental convergence: The required conditions for plate accretion Accretion, in geology, is a process by which sediment is added to a tectonic plate. ...

As such, the basement rock can become younger going closer to the edge of the continent. There are exceptions of however, such as exotic terranes. Exotic terranes are pieces or fragments of other continents that have broken off their original parent continent and have become accreted to a different continent. An exotic terrane is a piece or fragment of continent that has broken off from its parent continent and become accreted to another continent. ...

Also, many continents can consist of several continental cratons - blocks of crust built around an initial original core of continents, that gradually grew and expanded as additional newly created terranes were added to their edges. For instance, Pangea consisted of most of the Earth's continents being accreted into one giant supercontinent. Most continents indeed have several continental cratons, in other words they are made up of the accretion of many smaller continents, such as Asia, Africa, and Europe. World geologic provinces. ... Pangea may refer to: a common alternative spelling of the name Pangaea given to the supercontinent that is believed to have existed during the Paleozoic and Mesozoic eras Pangea, a geology equipment supplier/developer of mineralogical testing equipment Pangea (cable system), a submarine telecommunications cable system connecting the Netherlands and... In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... World map showing the location of Asia. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... World map showing the location of Europe. ...

Sources

• Parker, Sybil P. (Ed.). 1997. McGraw-Hill Dictionary of Geology and Mineralogy. New York: McGraw-Hill.
• Bates, Robert L. and Julia A. Jackson (Eds.) 1994. Dictionary of Geological Terms. American Geological Instutute. New york: Anchor Books, Doubleday Dell Publishing.