How is oceanic crust formed?
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Oceanic crust is formed by volcanism at the mid-ocean ridges, also called spreading centers. Magma upwells from within the asthenosphere or mantle. It often does not erupt onto the sea floor but rises through complex cracks and fissures where it encounters cooler rock and sea water. Other areas actively erupt and lava flows in sheets typically less than 10 meters thick. For example, at the Juan de Fuca Ridge, the process creates about 6 meters of new crust in 100 years. Oceanic crust consists of basalt, often referred to as MORB (mid-ocean ridge basalt).
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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. This magma can be derived from either the Earth's mantle or pre-existing rocks made molten by extreme temperature and pressure changes. Over 700 types of igneous rocks have been described, most of them formed beneath the surface of the Earth's crust. The word "igneous" is derived from the Latin ignis, meaning "fire".
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The Earth is formed of several layers that have very different physical and chemical properties. The outer layer, which averages about 70 kilometers in thickness, consists of about a dozen large, irregularly shaped plates that slide over, under and past each other on top of the partly molten inner layer. Most earthquakes occur at the boundaries where the plates meet. In fact, the locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries. \nThere are three types of plate boundaries: spreading zones, transform faults, and subduction zones. At spreading zones, molten rock rises, pushing two plates apart and adding new material at their edges. Most spreading zones are found in oceans; for example, the North American and Eurasian plates are spreading apart along the mid-Atlantic ridge. Spreading zones usually have earthquakes at shallow depths (within 30 kilometers of the surface).  \n\nTransform faults are found where plates slide past one another. An example of a transform-fault plate boundary is the San Andreas fault, along the coast of California and northwestern Mexico. Earthquakes at transform faults tend to occur at shallow depths and form fairly straight linear patterns. \n\nSubduction zones are found where one plate overrides, or subducts, another, pushing it downward into the mantle where it melts. An example of a subduction-zone plate boundary is found along the northwest coast of the United States, western Canada, and southern Alaska and the Aleutian Islands. Subduction zones are characterized by deep-ocean trenches, shallow to deep earthquakes, and mountain ranges containing active volcanoes.\n\nEarthquakes can also occur within plates, although plate-boundary earthquakes are much more common. Less than 10 percent of all earthquakes occur within plate interiors. As plates continue to move and plate boundaries change over geologic time, weakened boundary regions become part of the interiors of the plates. These zones of weakness within the continents can cause earthquakes in response to stresses that originate at the edges of the plate or in the deeper crust. The New Madrid earthquakes of 1811-1812 and the 1886 Charleston earthquake occurred within the North American plate.
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Convergent boundaries move toward each other - in oceanic/continental convergence volcanic mountains form; the same for oceanic/oceanic convergence except they are usually referred to as island arcs such as the Aleutian Islands off the coast of Alaska; in continental/continental convergence, mountain ranges are formed such as the Himalayas & Appalachians\n\nDivergent boundaries move away from each other making the crust thinner - rift valleys such as that in Africa in continental divergent boundaries; oceanic ridges such as the Mid Atlantic Ridge in the Atlantic Ocean\n\nTransform boundaries slide past each other horizontally & don't really create any kind of landform that I know of. They just offset things like in California w/ the San Andreas fault. It has been known to move fences & rows of trees out of line.
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These are all related to the crusts. \n\nA divergent boundary occurs when two Earth tectonic plates move away from each other, causing a depression or a range. \n\nSubduction occurs underwater when seawater tectonic plates converge into continental plates. Since seawater tectonic plates are more dense than continental plates, it 'subduct's and goes under. \n\nThere's more than 3 types of magma, depending on its temperature, density, and composition.\n\nAs you know, the plate tectonics theory says that the Earth's crust is moving constantly. By applying the observations of divergent boundaries through time (ex, Great Rift Valley created over centuries), that will -support- and -clarify- the plate tectonics theory. So, divergent boundaries being observed serves as evidence and support for the theory.\n\nSubduction occurs in sea-floor spreading, which explains why crusts closer to the mid-atlantic ridge are "warmer" and "younger", while the ones further away, and most likely closer to a subduction zone is colder. This shows that the Earth's crust is once again moving, once again indicating that the theory is true. \n\nMagma is formed when divergent boundaries move away from each other, and is replaced by new crusts formed by magma. The cycle of sea-floor spreading undergoing subduction, sinking under the continental crust, melting into magma, then re-forming  at the Mid-Atlantic ridge.
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At Divergent Margins, plates move apart and new crust and lithosphere are created. This usually occurs at a Mid-Ocean Ridge, but divergent margins can also occur on land. The Great Rift Valley of Africa is a example of a divergent margin that is splitting the African Continent into two parts. Eventually, as the rift continues to open, a new ocean basin will be formed. \nWhere Oceanic Plates move apart, Magma wells up from the Mantle and crystallizes against the trailing edges of the plates. This is how new Oceanic Lithosphere is formed. Spreading across Mid-Ocean Ridges is symmetrical, and Normal Faulting predominates. Earthquakes are weak but common. As this new, hot Lithosphere cools and moves away  from the Mid-Ocean Ridge it Isostatically adjusts and settles lower into the Mantle, increasing the depth of the sea floor. This change produces characteristic Mid-Ocean Ridge Stratigraphy. \n\nSea floor Volcanism and Hydrothermal Activity are common along Mid-Ocean Ridges. \n\nMagma cooling at Mid-Ocean Ridges continuously records variations in the polarity of the Earth's magnetic field.
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a) Earth's surface is made up of about a dozen enormous slabs, or plates. The slow movement of these plates across the surface is called continental drift, or plate tectonics. \n\nb) the outermost level of the land or sea; "earthquakes originate far below the surface"; "three quarters of the Earth's surface is covered by water" \n\nc) Is a kind of layer  (a relatively thin sheetlike expanse or region lying over or under another )
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The crust and mantle are generally solid.  The inner and outer core are molten rock and metal...very dense, but still liquid.
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Abyssal planes are created because sediment buries the otherwise rugged topography of the ocean crust.  This sediment is transported largely by things called turbidity currents (http://en.wikipedia.org/wiki/Turbidity_current).  The Atlantic basin is ringed primarily by passive continental margins which allow these currents to transport the sediments well out into the basins.  However, the Pacific ocean is ringed primarily by subduction zones.  Subduction zones are usually marked by features that we call deep ocean trenches.  These trenches are the deepest features of the ocean basins.  As turbidity currents come off the continental margins in the Pacific, they usually continue down into the trenches where they become trapped.  Therefore, the sediment they carry does no make it out into the Pacific basin.  This is why there are fewer abyssal plains in the Pacific than there are in the Atlantic.
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The process as a whole is known as 'continental drift,' or 'plate tectonics'. This process is further divided into several processes: divergence, or where plates are moving away from one another as a result of lava welling up and cooling in a mid-ocean ridge; convergence, where two plates collide and either form mountains or subduct depending on their types; and transformance, where tow plates move at opposite directions parallel to one another. \n\nKnowing this, your question can be answered. You are describing convergance between either two oceanic plates or one oceanic plate + one continental plate. The process is also known as subduction, and can form large mountains and volcanic/seismic activity.
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Currently there are over five thousand active volcanoes underwater varying from ones larger than any on the surface to cones no larger than an automobile. The net reslut of this action is thermal heating of the oceans, at key positions, which in turn reaches the surfaceto be carried aloft into the atmosphere to become part of our surface weather pattern system. As the oceans are heated winds of a high velocity are created and driven over the land areas due to temperature differential. \n\nIn the Pacific Ocean there are ocean basins - volcanoes, of which there are estimated to be about 20,000 on the ocean bottoms of the world. Some of these form single mountains, and others join with other volcanoes to form ridges. The highest ones rise above the surface of the water as islands, which in many cases linear groups such as the Hawaiian Islands. \n\nIsland groups are simply the highest summits of ridges. The submerged part of the Hawaiian Islands is among the largest and longest of these volcanic ridges--more than 1,500 miles (2,400 kilometers) long. \n\nMany island groups of the Pacific are linear in form, with the largest and highest island of the group at one end and the lowest and smallest at the other. This feature is true of the Hawaiian Islands, explained as the result of intermittent movement of the tectonic plate over what is called a hot spot. \n\nMolten volcanic material is ejected from it and results in the formation of a large mass of material if the plate pauses for a sufficient length of time at the spot. In this way a volcanic island, or ridge, is built. The plate moves, and another part of it lies over the hot spot, receiving fresh volcanic material. Meanwhile the older material, if it has become an island, is subject to erosion and thus is worn down.
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The earth has evolved geologically, chemically, and biologically.  Geologically:  When the earth formed, it was basically a molten mass.  It cooled, and settled into layers, with the densest layers in the center, and the least dense in the crust.  The atmosphere of the early earth was basically methane, ammonia, hydrogen, carbon dioxide, and water vapor.  The hydrogen escaped, the carbon of the carbon dioxide bonded with rock.I don't recall what happened to the rest.  But, when life began, it was life that found oxygen a poison.  However, when photosynthetic organisms appeared, they actually produced oxygen as a waste product.  Some forms of life evolved to be able to use the oxygen to permit them to more efficiently extract the energy from organic compounds.  As far as life itself is concerned, the first organisms, according to the current model, were extremophiles - they were one celled organisms living in extreme environments, such as the volcanic vents on the ocean floor.  Life gradually evolved from simple unicellular to more complex unicellular to multicellular.  Geologically, when the earth was new, there was very little land.  As a result of volcanic activity, grantic crust formed, which underlies the continents.  The continents, or rather the crustal plates on which they "float" have been moving since they formed due to convection currents within the earth's mantle.  So, the layout of the land forms has been changing, and with them, the ocean currents.  This has resulted in a gradual and constant change in climate.
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True. Magma can be generated at subducted plate boudaries. \n\nI am still uncertain about the question. Does your question read as "Can magma be formed at subducted plate boundaries" then the answer would be yes
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tectonic plates are giant pieces of the Earth's crust.  They "float" on the mantle, a layer of liquid rock under the crust.  The plates are constantly moving.  A mountain range is formed when two plates moving toward each other collide.  One plate will "run over" the other.  When this happens the top plate gets pushed up and the bottom pushed into the mantle.  The top plate will rise to form a mountain range.\n\nClimate and erosion give the mountain range its finished look (paint on the car).  The tectonic movement gives it its general shape.
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The Earth's crust is made of plates.\nThe plates move, like ice floating on a lake.\nConvergant means comming together.  When plates move toward each other, they collide.\nDivergant means moving apart.  When plates moves apart they form a trench at the boundry.\n\ntransform boundary (also known as slip boundary) is said to occur when tectonic plates slide and grind sideways against each other.
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Not much water in the form of free liquid water entrapped in pores of the rocks in subducted lithosphere that makes it into the mantle. However, the subducted plate *does* contain a substantial amount of water in the form of hydrous minerals  (e.g., clays, serpentine, amphiboles, chlorite, epidote, micas, etc.) that form by hydrothermal alteration of the oceanic crust, and are present in the overlying sediments (some of which are subducted).\n\nMuch of the water in these hydrous minerals is released when the subducted plate heats up as it is warmed by the hot mantle surrounding the plate, and the hydrous minerals dehydrate (really just a special type of prograde metamorphism).  The water that is released is thought to leave the plate itself and rise (because it is less dense than the rock, and hence bouyant) into the overlying mantle.  Water reduces the temperature at which  silicate rocks begin to melt, and because the mantle overlying the subducted slab is actually hotter than the slab itself, this water can trigger melting in the mantle.  This is why there is almost always a volcanic front above a subduction zone (e.g., the "Pacific ring of fire").  The magma associated with these subduction-zone volcanoes is usually volatile-rich (water and CO2 coming from hydrous minerals and carbonates in the subducted slab), and gives rise to explosive eruptions like Mt. St. Helens, or in a more extreme example, Krakatoa.
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At convergent plate boundaries two plates collide and the heavier of the two plates is forced beneath the lighter one. As the heavier plate gets pushed down deep into the earth it begins to melt and forms molten magma. This magma slowly migrates upwards through the earth's crust where it then errupts onto the earth's surface as lava, eventually forming volcanoes. \n\nAt divergent plate zones two plates move apart from each other. When this happens a crack forms in the earth's crust. Magma from below moves upwards into this crack to fill the void 'so to speak'. Once again this magma errupts onto the earth's surface as red hot lava and we have the formation of active volcanoes.