 The thickness of the Earth's crust (km). The continental crust is the layer of granitic, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. Consisting mostly of sialic rock, it is less dense than the material of the Earth's mantle, which consists of mafic rock. Continental crust is also less dense than oceanic crust, though it is considerably thicker; mostly 35 to 40 km versus the average oceanic thickness of around 7-10 km. About 40% of the Earth's surface is now underlain by continental crust. Image File history File links No higher resolution available. ...
Image File history File links No higher resolution available. ...
For other uses, see granite (disambiguation). ...
Two types of sedimentary rock: limey shale overlaid by limestone. ...
Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form, derived from the Greek words meta, change, and morphe, form. The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound...
Animated, colour-coded map showing the various continents. ...
Sediment Rock Mantle The global continental shelf, highlighted in cyan The continental shelf is the extended perimeter of each continent, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs. ...
typical Sial material, a Precambrian granite showing potassium feldspar (felsic) matrix For the Sial tribe of Pakistan, see Sial (tribe). ...
In mathematics, the term dense has at least three different meanings. ...
Earth cutaway from core to exosphere. ...
In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ...
Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ...
As a consequence of the density difference, when active margins of continental crust meet oceanic crust in subduction zones, the oceanic crust is typically subducted back into the mantle. Because of its relative low density, continental crust is only rarely subducted or re-cycled back into the mantle (for instance, where continental crustal blocks collide and overthicken, causing deep melting). For this reason the oldest rocks on Earth are within the cratons or cores of the continents, rather than in repeatedly recycled oceanic crust; the oldest continental rock is the Acasta Gneiss at 4.01 Ga, while the oldest oceanic crust is of Jurassic age. Categories: Geology stubs | Plate tectonics ...
Categories: Geology stubs | Plate tectonics ...
World geologic provinces. ...
Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ...
The Acasta Gneiss is a rock outcrop of Archaean tonalite gneiss in the Northwest Territories, Canada. ...
Annum is a Latin noun meaning year. ...
The Jurassic Period is a major unit of the geologic timescale that extends from about 199. ...
The height of mountain ranges is usually related to the thickness of crust. This results from the isostasy associated with orogeny (mountain formation). The crust is thickened by the compressive forces related to subduction or continental collision. The buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, which is where the thickest crust is found. Isostasy is a term used in Geology to refer to the state of ice above stasy and is angravitational equilibrium between the Earths lithosphere and asthenosphere such that the tectonic plates float at an elevation which depends on their thickness and density. ...
// Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within...
The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone. ...
The thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust. The edges of continental fragments formed this way (both sides of the Atlantic Ocean, for example) are termed passive margins. In geology, a rift is a place where the Earths lithosphere is expanding. ...
Old fault exposed by roadcut near Harrisburg, Pennsylvania. ...
Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ...
In plate tectonics, a passive margin is the normally gently sloping continental shelf area located on the trailing edge of a drifting continent. ...
The high temperatures and pressures at depth, often combined with a long history of complex distortion, mean that much of the lower continental crust is metamorphic - the main exception to this being recent igneous intrusions. Igneous rock may also be "underplated" to the underside of the crust, i.e. adding to the crust by forming a layer immediately beneath it. 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. ...
Devils Tower, an igneous intrusion exposed when the surrounding softer rock eroded away. ...
It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model indicates that at prior to 3.7 Bya continental crust constituted less than 10% of the present amount. By 3.0 Bya the amount was about 25% and following a period of rapid crustal evolution it was about 60% of the current amount by 2.6 Bya (Taylor and McLennan, 1995). The growth of continental crust appears to have occurred in spurts of increased activity corresponding to five episodes of increased production through geologic time (see graphic at Butler). New material can be added to the continents by the partial melting of oceanic crust at subduction zones, causing the lighter material to rise as magma, forming volcanoes. Also, material can be accreted "horizontally" when volcanic island arcs, seamounts or similar structures collide with the side of the continent as a result of plate tectonic movements. Mariana Islands, an oceanic island arc Cascade Volcanic Arc, a continental volcanic arc A volcanic arc is a chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma. ...
A seamount is a mountain rising from the ocean seafloor that does not reach to the waters surface (sea level), and thus is not an island. ...
References - Butler, Rob, Making new continents Accessed 01/29/2006
- Saal, A.L., Rudnick R.L., Ravizza G.E. & Hart S.R., 1998. Re-Os isotope evdence for the composition, formation and age of the lower crust. Nature, 39317, 1998.
- Taylor and McLennan, 1995, Model of growth of continental crust through time in John Victor Walther, 2005, Essentials Of Geochemistry, Jones & Bartlett, ISBN 0-7637-2642-7
- von Huene, R. and D.W. Scholl, 1991. "Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust." Reviews of Geophysics, 29, 279-316.
Isotope geochemistry is an aspect of Geology based upon study of the relative and absolute concentrations of the elements and their isotopes in the Earth. ...
See also typical Sial material, a Precambrian granite showing potassium feldspar (felsic) matrix For the Sial tribe of Pakistan, see Sial (tribe). ...
Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ...
World geologic provinces. ...
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. ...
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