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Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima. It is thinner than continental crust, or sial, generally less than 10 kilometers thick, however it is more dense, having a mean density of about 3.3 grams per cubic centimeter. Download high resolution version (1624x1020, 895 KB)Age of oceanic crust. ...
Download high resolution version (1624x1020, 895 KB)Age of oceanic crust. ...
The tectonic plates of the Lithosphere on Earth. ...
Animated map exhibiting the worlds oceanic waters. ...
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. ...
Sima is the name for the lower layer of the Earths crust. ...
typical Sial material, a Precambrian granite showing potassium feldspar (felsic) matrix For the Sial tribe of Pakistan, see Sial (tribe). ...
For other meanings of gram, see gram (disambiguation). ...
A cubic centimetre (cm3) is an SI derived unit of volume, equal to the volume of a cube with side length of 1 centimetre. ...
Composition Although a complete section of oceanic crust has not yet been drilled, there are estimations of composition based on analyses of ophiolites, comparison of seismic structure of the oceanic crust with laboratory determinations of seismic velocities in known rock types, and samples recovered from the ocean floor by submersibles, dredging (especially from ridge crests and fracture zones) and drilling. Oceanic crust is significantly simpler than continental crust and generally it can be divided in three layers. Ophiolites are sections of oceanic lithosphere that have been uplifted or emplaced to be exposed within continental crustal rocks. ...
This article needs additional references or sources for verification. ...
The thickness of the Earths crust (km). ...
- Layer 1 consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Near the continental margins sediment is terrigenous, meaning derived from the land, unlike deep sea sediments which are made of tiny shells of marine organisams, usually calcareous and siliceous, or it can be made of volcanic ash and terrigenous sediments transported by turbidity currents. [1]
- Layer 2 could be divided into two parts: layer 2A – 0.5 km thick uppermost volcanic layer of glassy to finely crystaline basalt usually in form of pillow basalt, and layer 2B – 1.5 km thick layer composed of diabase dikes.
- Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbros and cumulate ultramafic rocks. It constitutes over two-thirds of oceanic crust volume with almost 5 km thickness.
Oceanic Ridge Oceanic crust is formed at an oceanic ridge, while the lithosphere is subducted back into the asthenosphere at trenches. ...
A turbidity current or density current is a current of of rapidly moving, sediment-laden water moving down a slope through air, water, or another fluid. ...
For the cities, see Basalt, Colorado and Basalt, Idaho. ...
It has been suggested that this article or section be merged with Dolerite. ...
A dike in geology refers to a tabular intrusive igneous body. ...
Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ...
Gabbro specimen. ...
Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. ...
Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ...
Geochemistry The most voluminous eruptive rocks composing ocean floor are mid-ocean ridge basalts (MORBs), which are derived from low-potassium tholeiitic magmas. These rocks have low concentrations of large ion litophile elements (LILE), light rare earth elements (LREE), volatile elements and other highly incompatible elements (Th, U, Nb, Ta and Pb). There can be found MORBs enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland. [2] General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ...
Incompatible element is a term used in petrology and geochemistry. ...
In geology, a hotspot is a location on the Earths surface that has experienced active vulcanism for a long period of time. ...
NASA Satellite photo of the Galápagos archipelago. ...
Motto (Portuguese for Rather die free than in peace subjugated) Anthem (national) (local) Capital Ponta Delgada1 Angra do HeroÃsmo2 Horta3 Largest city Ponta Delgada Official languages Portuguese Government Autonomous region - President Carlos César Establishment - Settled 1439 - Autonomy 1976 Area - Total 2,333 km² (n/a) 911 sq mi...
Life Cycle Oceanic crust generally does not last longer than 200 million years. It is continuously being created at oceanic ridges. At these ridges, hot magma rises into the crust and cools, pushing the crust apart at the ridge. The continuous formation of new oceanic crust pushes the older crust away from the mid-ocean ridge. As it moves away from the ridge, the crust becomes cooler and denser, while the sediment may build on top of it. Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ...
The oceanic crust subducts toward the mantle at what are known as convergent boundaries. These boundaries can exist between two oceanic plates or between an oceanic and a continental plate. At oceanic plate-continental plate boundaries, the oceanic plate always subducts because the continental crust is less dense. The subduction process is why oceanic crust lasts a maximum of 200 million years. Plate tectonics is the study of these processes. The Juan de Fuca plate sinks below the North America plate at the Cascadia subduction zone. ...
In plate tectonics, a convergent boundary (convergent fault boundary, convergent plate boundary, or active margin) is where two tectonic plates slide towards each other and usually collide forming either a subduction zone with its associated island arc or an orogenic belt and associated mountain range. ...
The tectonic plates of the world were mapped in the second half of the 20th century. ...
Magnetic Lines -
The oceanic crust displays an interesting pattern of parallel magnetic lines, parallel to the ocean ridges, frozen in the basalt. In the 1950’s, scientists mapped the magnetic field generated by rocks on the ocean floor. They noticed a symmetrical pattern of positive and negative magnetic lines as they moved along the ocean floor, and the line of symmetry was at the mid ocean ridge. The fact that the anomalies were symmetrical at the mid-ocean ridge was explained by the hypothesis that new rock was being formed by magma at the mid-ocean ridges, and the ocean floor was spreading out from this point. When the magma cooled to form rock, it aligned itself with the current position of the north magnetic pole of the Earth (which has reversed many times in its past) at the time of its cooling. New magma forced the older cooled magma away from the ridge. Approximately half of the new rock was formed on one side of the ridge and half on the other. Age of oceanic crust. ...
Recent geomagnetic reversals. ...
References - ^ D. R. Bowes (1989) The Encyclopedia of Igneous and Metamorphic Petrology, Van Nostrand Reinhold ISBN: 0-442-20623-2
- ^ Clare P. Marshall, Rhodes W. Fairbridge (1999) Encyclopedia of Geochemistry, Kluwer Academic Publishers ISBN: 0-412-75500-9
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