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Topic: Continental crust


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In the News (Tue 23 Apr 19)

  
  Continental crust - Wikipedia, the free encyclopedia
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.
Continental crust is also less dense than oceanic crust, though it is considerably thicker; 20 to 80 km versus the average oceanic thickness of around 5-10 km.
The thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust.
en.wikipedia.org /wiki/Continental_crust   (521 words)

  
 Crust (geology) - Wikipedia, the free encyclopedia
The crust of the Earth is composed mainly of basalt and granite.
The oceanic crust (sima) is 5 to 10 km thick and is composed primarily of a dark, dense rock called basalt.
The continental crust (sial) is 20-70 km deep and is composed of a variety of less dense rocks.
en.wikipedia.org /wiki/Crust_(geology)   (427 words)

  
 Encyclopedia: Continental crust
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.
A craton is an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years.
The crust is the outermost layer of the earth (not counting the atmosphere).
www.nationmaster.com /encyclopedia/Continental-crust   (1103 words)

  
 Average Composition of the Earth's Continental Crust
There is some utility in having an estimate of the concentrations of elements in the continental crust as opposed to the sub-oceanic crust, mantle and core, partly for the development of theory of crustal evolution, and as an addition to our general store of knowledge.
The true original unmodified composition of the continental crust therefore may be taken as being an average of all andesites and their related rocks erupted since the earliest Archaean time.
The evolution of the crust appears to parallel the evolution of the andesites, from a basalt or basaltic-andesite average composition in the barely emergent proto arcs towards andesite in the continental arcs.
www.geokem.com /earths_average_composition.html   (1401 words)

  
 Continental crust composition constrained by measurements of crustal Poisson's ratio   (Site not responding. Last check: 2007-11-05)
Continental crust composition constrained by measurements of crustal Poisson's ratio
The main uncertainties are associated with the composition of the lower crust.
Our results strongly support the presence of a mafic lower crust beneath cratons, and suggest either a uniformitarian craton formation process involving delamination of the lower crust during continental collisions, followed by magmatic underplating, or a model in which crust formation processes have changed since the Precambrian era.
www.nature.com /nature/journal/v374/n6518/abs/374152a0.html   (487 words)

  
 CONTINENTAL DRIFT - Paleontology and Geology Glossary   (Site not responding. Last check: 2007-11-05)
In 1915, the German geologist and meteorologist Alfred Wegener first proposed the theory of continental drift, which states that parts of the Earth's crust slowly drift atop a liquid core.
Oceanic crust (the crust under the oceans) is thinner and denser than continental crust.
Crust is constantly being created and destroyed; oceanic crust is more active than continental crust.
www.enchantedlearning.com /subjects/dinosaurs/glossary/Contdrift.shtml   (992 words)

  
 Savage Earth: Hell's Crust
At the thinnest spots in the oceans, where new crust is created, it is only a few miles thick; on the continents, the crust averages about 20 miles thick.
The creation of crust at mid-ocean ridges "accounts for about ninety-five percent of the volcanic activity on Earth," says geophysicist Don Forsyth of Brown University, a principal investigator on the MELT project, which is conducting a detailed study of how melted rock flows from the mantle and into the spreading centers.
The new crust eventually cools, and over time it is pushed to the side by still more melted rock rising up from within the Earth, in a continuous process.
www.pbs.org /wnet/savageearth/hellscrust   (1537 words)

  
 Continental Drift   (Site not responding. Last check: 2007-11-05)
This balance between the weight of the continental and oceanic crust and the internal forces that cause them to float is known as the principle of isostasy.
On the other hand, the continental crust is thicker and older, and, being largely composed of aluminum silicates in addition to magnesium.
This is the boundary at which the crust and the mantle meet, and it is characterized in seismograms as a place where seismic waves change speed rapidly.
www.oceansonline.com /continen.htm   (3039 words)

  
 Earth - Hutchinson encyclopedia article about Earth   (Site not responding. Last check: 2007-11-05)
At an ocean–continent destructive margin, ocean crust is forced under the denser continental crust, forming an area of volcanic instability.
It is almost spherical, flattened slightly at the poles, and is composed of five concentric layers: inner core, outer core, mantle, crust, and atmosphere.
The crust and the uppermost layer of the mantle form about twelve major moving plates, some of which carry the continents.
encyclopedia.farlex.com /Earth   (716 words)

  
 Moving Continents: Images of Continental Drift   (Site not responding. Last check: 2007-11-05)
The phenomena is known as continental drift and the process has been going on for hundreds of millions of years-- at rates measured in only a few centimeters per year.
Although proposed nearly a century ago, continental drift became accepted only after intriguing evidence from mapping of undersea mountain ranges during World War II and subsequent studies of the ocean floor and continental margins produced nearly irrefutable evidence.
The study of continental drift, it's history and the forces that cause it, constitutes the branch of geology known as Plate Tectonics.
www.clearlight.com /~mhieb/WVFossils/continents.html   (614 words)

  
 Earth's Crust, Lithosphere and Asthenosphere
Crust, the upper layer of the Earth, is not always the same.
Crust under the oceans is only about 5 km thick while continental crust can be up to 65 km thick.
Also, ocean crust is made of denser minerals than continental crust.
www.windows.ucar.edu /cgi-bin/tour_def/earth/interior/earths_crust.html   (246 words)

  
 Mountains formed by plate convergence   (Site not responding. Last check: 2007-11-05)
Oceanic crust is recycled at subduction zones where one leading edge of convergent lithospheric plates is subducted beneath the other and remelted.
Continental crust is composed of material less dense than oceanic crust so it floats on the mantle rather than being subducted into the asthenosphere.
Spectacular mountains result from the collision of continental crust as tectonic plates collide, buckling and bunching continental crust along their impinging plate margins.
www.clearlight.com /~mhieb/WVFossils/collision.html   (960 words)

  
 Can delamination of lower crust explain the continental crust paradox
The upper continental crust is too evolved (felsic) to be a melt in equilibrium with the mantle (e.g., basalt).
One possibility is the lower crust because it is mafic.
However, the composition of the average global lower continental crust (Rudnick and Fountain, 1995) is clearly not mafic enough to balance the evolved composition of the continental crust.
www.ruf.rice.edu /~ctlee/lowercrust.htm   (239 words)

  
 Active Skim View of: IV. Characterization of Continental Crust
In the continental crust, this may vary anywhere from 15 50 km, depending on heat flow and the thermal properties of the rocks.
Continental crystal studies ' + 'are probably at a stage of development equivalent to that reached in the study of oceanic crust 20 years ago.
The lower crust in volcanic regions, particularly in ' + 'rift valleys, appears to be in the granulite metamorphic facies and appears to have two-pyroxene granulites of basaltic composition as a component.
www.nap.edu /nap-cgi/skimit.cgi?isbn=0309029287&chap=115-158   (11410 words)

  
 Nat' Academies Press, Continental Tectonics (1980)
In particular, continental volcanism seems sensitive to the age and composition of the immediately underlying lithosphere, as well as to the geometry of major structural flaws.
Recent Pb and Sr isotopic studies of continental vol- canic rocks in the western United States indicate that the isotopic composition of volcanic rocks reflects the age and composition ofthe underlying lithosphere, demonstrating major compositional control by the lower crust or the li~- osphenc upper mantle.
Continental molasse is devel- oped in both regions at the close of the geosynclinal evo- lution.
www.nap.edu /books/0309029287/html/159.html   (10013 words)

  
 Continental freeboard, sedimentation rates and growth of continental crust   (Site not responding. Last check: 2007-11-05)
Of the two contrasting models, the first and most popular is that the continental crust of the Earth has grown throughout geological time.
The second model argues that the present mass of the continental crust formed very early in Earth history (>4,000 Myr) and has subsequently been recycled through the mantle in a steady-state fashion such that the mass of the crust has not changed during most of Earth history
We point out here that although the record of continental freeboard is consistent with either limited growth or no-growth models, recent sedimentation rates appear insufficient to support no-growth models.
www.nature.com /nature/journal/v306/n5939/abs/306169a0.html   (496 words)

  
 Continental Drift   (Site not responding. Last check: 2007-11-05)
Passive margins are where continental crust is being rafted or pushed along by oceanic crust
Continental crust may be “rafted” along with oceanic crust
Continental crust is not subducted along with the oceanic crust
www.weather.brockport.edu /~mnoll/Mod5notes.htm   (756 words)

  
 Crust - Pie Crust Recipe   (Site not responding. Last check: 2007-11-05)
These two types of crust differ in their average age, composition, The crust beneath Antarctica is continental, but it is surrounded by the oceanic
The crust covers the mantle and is the earth's hard outer shell, the surface on which we are living.
Cryptogamic crust covers the surface of soil between grasses, shrubs, This layer is called a cryptogamic crust.
crust.surferfind.com   (219 words)

  
 Major Constituents of the Continental Crust
Dissolved salts are ultimately derived from the continental crust, and move through both the hydrologic cycle and the plate tectonics cycle.
Salt ions are derived from the mechanical and chemical breakdown of continental crust, from volcanic emissions, from ridge emissions, and from the decay
If sea salts ultimately come from the continental crust, we might expect the composition of seawater to resemble the composition of the continental crust.
talc.geo.umn.edu /courses/1006/Fall01_night/Salts.html   (1081 words)

  
 Continental Crust Mass Balance Calculation
The exercise uses geochemical data for average quartz monzonite and diorite from the Mineral Mountains in Utah.
The students do mass balance calculations and are asked to relate their calculations to continental crust formation.
Data and/or figures from papers about continental crust such as Rudnick and Fountain, 1995, or Taylor and McClennan, 1985, may help students to make connections between the calculations they have made and what the crust looks like.
serc.carleton.edu /quantskills/workshopactivities/crust_mass.html   (694 words)

  
 Continental crust under compression: A seismic refraction study of South Island Geophysical Transect I, South Island, ...
Continental crust under compression: A seismic refraction study of South Island Geophysical Transect I, South Island, New Zealand
As part of this study, two seismic refraction lines were shot across central South Island and offshore extensions of the continental crust in the Tasman Sea and Pacific Ocean.
Continental compression has locally reduced the seismic velocities in the Pacific plate crust by 0.2–0.3 km/s, a possible effect of high strain and fluids in the crust.
www.agu.org /pubs/crossref/2004/2003JB002790.shtml   (413 words)

  
 Conditions for flow in the continental crust
Earthquake focal depth distributions and effective elastic thickness variations on the continents suggest that in old cold regions such as shields, the lower continental crust can be stronger than the upper mantle, and imply that the upper mantle can flow even when the lower crust does not.
We suggest that the lower crust only flows when its viscosity is significantly reduced, either by heating from igneous intrusions or by the addition of water.
The timescale is controlled either by conductive cooling of intrusions, or by the separation of melt from its matrix, which removes the water.
www.agu.org /pubs/crossref/2002/2002TC001394.shtml   (218 words)

  
 MSN Encarta - Dictionary - continental crust definition
MSN Encarta - Dictionary - continental crust definition
part of Earth's crust underlying continents: the part of the outer shell of Earth that constitutes the continents and the rocks beneath them down to the level of the mantle.
It is approximately 35 km (22 mi) thick in most areas and is composed of sedimentary rocks near the surface and metamorphic rocks at a lower depth.
encarta.msn.com /dictionary_1861688262/continental_crust.html   (104 words)

  
 What is the crust.   (Site not responding. Last check: 2007-11-05)
The crust is relatively cold and brittle compared to the layers that are deeper down.
Oceanic crust consists of young basalt, is about 5 km thick, and is presently forming at mid-ocean ridges.
After a while the two sides of the ridge pull apart, and soon new basalt comes up to again fill the crack.
volcano.und.nodak.edu /vwdocs/frequent_questions/grp9/question88.html   (159 words)

  
 Practice questions: Ocean and Continental Crust
Which seafloor province is underlain by continental crust?
What is the age order of sea floor types (the crust underlying them) from oldest to youngest?
Continental shelf, abyssal plains, abyssal hills, mid-ocean ridge.
www.usd.edu /esci/exams/ocencont.html   (261 words)

  
 INDIRECT EVIDENCE OF CONTINENTAL CRUST
Assuming Airy isostasy and in the complete absence of any evidence of excessive volcanism or thermal uplift from plume activity, this indicates the sites were underlain by only slightly thinned continental crust at that time.
Hence, here too, the evidence suggests the site originally lay in water depths of at most a few hundred meters, which again indicates the underlying crust is almost certainly continental, before it subsided during the Cretaceous.
The mafic basement cores from Sites 1067 and 900 are also considered to represent lower continental crust.
www-odp.tamu.edu /publications/173_SR/synth/cs_5.htm   (607 words)

  
 Age of the Earth - EvoWiki   (Site not responding. Last check: 2007-11-05)
Houtermans, F. (1953) "Determination of the Age of the Earth from the Isotopic Composition of Meteoritic Lead" Nuovo Cimento 10, 1623-1633,
Wilde S.A.,Valley J.W., Peck W.H., Graham C.M. (2001) "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4Gyr ago" Nature 409, 175-178
This page was last modified 18:47, 4 Jan 2006.
www.evowiki.org /index.php/Age_of_the_Earth   (531 words)

  
 Energy Citations Database (ECD) - Energy and Energy-Related Bibliographic Citations   (Site not responding. Last check: 2007-11-05)
Energy Citations Database (ECD) Document #6469769 - Continental crust: a geophysical approach
Availability information may be found in the Availability, Publisher, Research Organization, Resource Relation and/or Author (affiliation information) fields and/or via the "Full-text Availability" link.
For a journal article, please see the Resource Relation field.
www.osti.gov /energycitations/product.biblio.jsp?osti_id=6469769   (69 words)

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