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	Mid-ocean ridge - Wikipedia, the free encyclopedia
		A mid-ocean ridge or mid-oceanic ridge is an uplifting of the ocean floor that occurs when convection currents beneath the ocean bed force magma up where two tectonic plates meet at a divergent boundary.
		The mid-ocean ridges of the world are connected and form a single global mid-oceanic ridge system that is part of every ocean and also by far the longest mountain range on Earth.
		Because a mid-ocean ridge is submerged at very deep depths in the middle of the ocean, its existence was not even known until the 1950s, when it was discovered through surveys of the ocean floor conducted by research ships.
	en.wikipedia.org /wiki/Mid-oceanic_ridge (392 words)

	[No title]
		Greater understanding of the ocean floor and the discoveries of features like mid-oceanic ridges, geomagnetic anomalies parallel to the mid-oceanic ridges, and the association of island arcs and oceanic trenches occurring together and near the continental margins, suggested convection might indeed be at work.
		Scientists began to realize that the youngest regions of the ocean floor were along the mid-oceanic ridges, and that the age of the ocean floor increased as the distance from the ridges increased.
		Magma continuously wells upwards at the mid-oceanic ridges (arrows) producing currents of magma flowing in opposite directions and thus generating the forces that pull the sea floor apart at the mid-oceanic ridges.
	www.msstate.edu /dept/geosciences/geologymb/CD.htm (1651 words)

	Learning Objectives
		The idea that the sea floor spread away from mid-oceanic ridges and was subducted beneath a continent or island arc as a result of mantle convection was proposed by Harry Hess in the early 1960s.
		Sea-floor spreading explains the young age of the sea floor, loss of older oceanic crust, lack of pelagic sediment on the ridge crest, and increasingly older oceanic crust away from the ridge crest.
		Ridge crests, trenches, transform faults, and their associated features are capable of migration in response to changing mantle conditions.
	highered.mcgraw-hill.com /sites/0072826967/student_view0/chapter4/learning_objectives.html (1097 words)

	Plate Tectonics Basics
		Recognizing these anomalies and interpreting them in terms of new sea floor generation at mid-oceanic ridges was one of the key elements for the formulation of the plate tectonics theory.
		Like the mid-oceanic ridges, the trenches are seismically active, but unlike the ridges they have low levels of heat flow.
		Magma continuously wells upwards at the mid-oceanic ridges and generates the forces that pull the sea floor apart at the mid-oceanic ridges.
	www.indiana.edu /~geol105/images/gaia_chapter_3/plate_tectonics_basics.htm (1098 words)

	The mechanism behind Plate Tectonics
		The mid-oceanic ridges rise 3000 meters from the ocean floor and are more than 2000 kilometers wide surpassing the Himalayas in size.
		This is evidence for continuous formation of new rock at the ridges.
		Scientists also began to realize that the youngest regions of the ocean floor were along the mid-oceanic ridges, and that the age of the ocean floor increased as the distance from the ridges increased.
	www.ucmp.berkeley.edu /geology/tecmech.html (865 words)

	10(p) Physiography of the Ocean Basins
		Oceanic rock is returned to the Earth's mantle when oceanic crust is subducted.
		In the center of the mid-oceanic ridge is a rift valley, between 30 to 50 kilometers wide, that dissects 1000 to 3000 meters deep into the ridge system.
		At the areas of subduction, oceanic crust is forced into the mantle after it collides with continental crust.
	www.physicalgeography.net /fundamentals/10p.html (1051 words)

	Classroom@Sea: The Carlsberg Ridge Cruise (Site not responding. Last check: 2007-10-19)
		Oceanic constructive margins are characterised by a central submarine spreading ridge where new oceanic crust is injected into the central rift.
		When magma is injected along the mid ocean ridge and cools, the iron-bearing minerals within the basalt align themselves according to the Earth’s magnetic field, so they preserve a record of the orientation of the Earth’s magnetic field at the time of crystallisation.
		The Mid Atlantic Ridge passes through the middle of Iceland, which is a volcanic island built up from lava extruded through the spreading ridge.
	www.soc.soton.ac.uk /CHD/classroom%40sea/carlsberg/science/oceanic_constr.html (977 words)

	McGraw-Hill AccessScience: Hydrothermal vent
		Most hydrothermal vents occur along the central axes of mid-oceanic ridges, which are underwater mountain ranges that wind through all of the deep oceans.
		The best-studied vents are at tectonic spreading centers on the East Pacific Rise and at the Mid-Atlantic Ridge.
		Major parts of the mid-oceanic ridges, including those of the Indian Ocean and Southern Hemisphere, are poorly explored, but available evidence suggests that these areas should also have extensive hydrothermal venting.
	www.accessscience.com /Encyclopedia/3/33/Est_330950_frameset.html?doi (247 words)

	Observing and learning : Archives - Plate tectonics page 3 (Site not responding. Last check: 2007-10-19)
		Therefore, the seafloor is a huge treadmill born from both sides of the mid-oceanic ridge (this phenomenon is known as "oceanic accretion") and plundging deep into the ocean trenches to be eventually recycled into the mantle.
		The "fast" ridges, like the East-Pacific ridge, don't feature a deep rift, as any cracks caused by their extensions are quickly hidden by abundant fluid lava and doughy lava flows.
		In all the cases, because of the gaps between the plates, faults parallel to the ridge are produced, hence numerous earthquakes.
	www.geospace-online.com /gol-en/sav/arc/sav-arc-tectonique3-en.htm (472 words)

	Vic Camp - spreading center volcanism
		The rise of this hot mantle provides thermal buoyancy to the ridge area and this is the reason that they stand as high ridges in the center of ocean basins.
		Oceanic crust is youngest near the ridge, but it becomes progressively older away from the spreading center due to divergence of the plates over time.
		Whereas oceanic crust is generated at divergent plate margins, it is consumed at convergent plate margins.
	www.geology.sdsu.edu /how_volcanoes_work/seafloorvol_page.html (363 words)

	Formation and Development of Fissures
		Oceanic crust is produced at the ridge in a neovolcanic zone 1-2 km wide and is subsequently fissured and tectonized by normal faults within 2-3 km of the ridge axis.
		On slow-spreading ridges the lithosphere is sufficiently thick and strong enough to support normal faulting right along the axis, and such faults may extend all the way to the base of the crust (e.g., Macdonald and Luyendyk [1977], Huang and Solomon [1988], and Kong et al.
		The structure of the ridge crest is related to both magmatic and tectonic processes that may be cyclic within a 2nd-, 3rd- or fourth-order ridge segment.
	dusk.geo.orst.edu /fissures (9661 words)

	Continental drift (Site not responding. Last check: 2007-10-19)
		South America and Africa are moving apart at 3 cm per year, due to the seafloor spreading along the Mid-Atlantic Ridge.
		New rock is created by volcanism at mid-ocean ridges and returned to the Earth's mantle at ocean trenches.
		Remarkably, in the 1928 AAPG volume, G. Molengraaf of the Delft Institute (now University) of Technology proposed a recognizable form of seafloor spreading in order to account for the opening of the Atlantic Ocean as well as the East Africa Rift.
	www.sciencedaily.com /encyclopedia/continental_drift (802 words)

	Ocean floor volcanism
		While spreading ridges at diverging plate boundaries have been extensively studied since the early 50's, it is only recently that comprehensive submarine explorations of intraplate volcanism were performed.The first European project on intraplate volcanism were initiated in 1986 in collaboration between several French and German institutes and universities.
		During fracturing and fissuring of the oceanic crust seawater penetrates into the lithosphere and it is heated in the vicinities of a magmatic reservoir.
		The fissuring and fracturing of the oceanic crust take place along the axis of the ridge; it is through such fissures that eruption of lava takes place.
	www.ifremer.fr /drogm_uk/Realisation/Vulgar/Volcanisme (1343 words)

	Ocean Deposits - Mining in Manitoba (Site not responding. Last check: 2007-10-19)
		VMS deposits may form as a result of mid-oceanic ridge basaltic magmatism, placing them at sites of extensional tectonic regimes, or as a result of oceanic arc and back-arc basin magmatism, placing them in subduction related tectonic environments.
		Ferromanganese nodules and encrustations occur both overlying basalt lava at mid-oceanic ridges where they are considered to be hydrothermal deposits, and overlying sediments away from ridge crests where they are considered hydrogenous or authegenic in origin.
		are thought to represent slices of oceanic crust that have been thrust or obducted onto a continental margin during collision.
	www.digistar.mb.ca /minsci/future/deposits.htm (613 words)

	Harry Hammond Hess [This Dynamic Earth, USGS]
		This interval is approximately the time needed for the ocean floor to move from the ridge crest to the trenches, where oceanic crust descends into the trench and is destroyed.
		Meanwhile, magma is continually rising along the mid-oceanic ridges, where the "recycling" process is completed by the creation of new oceanic crust.
		Finally, improved seismic data confirmed that oceanic crust was indeed sinking into the trenches, fully proving Hess' hypothesis, which was based largely on intuitive geologic reasoning.
	pubs.usgs.gov /publications/text/HHH.html (763 words)

	Oceans (Site not responding. Last check: 2007-10-19)
		Parts of the Mid-Atlantic Ridge, for example, which stretches from the Norwegian Sea to the South Atlantic, emerge as volcanic islands in Iceland and the Azores.
		The study of these features helped in the formulation of the theory of plate tectonics, and the recognition that mid-oceanic ridges are plate margins where new crustal rock is being formed as plates move apart, while the trenches mark where plates are being destroyed in subduction zones.
		The Marianas Trench, on the floor of the North Pacific Ocean, is the deepest known ocean trench, reaching a maximum depth of 11,033 metres (36,198 feet).
	www.pacificislandtravel.com /nature_gallery/oceans.html (1936 words)

	Mid-Oceanic Ridges, Flipping Polarity & Grand Unification (Site not responding. Last check: 2007-10-19)
		By taking core samples from the rock flowing away from the mid-oceanic ridges and dating them, it is possible to estimate the number of years it takes for changes such as this to occur.
		In analyzing the rock flowing away from the mid-oceanic ridges it is tempting for simplicity sake to assume that the rate of flow has always remained the same.
		Unfortunately, this assumption is not logical and greatly complicates the analysis of the ridges.
	www.grandunification.com /hypertext/Mid_Oceanic_Ridges.html (320 words)

	AA&ES - Moving Mountains - Plate Tectonics (Site not responding. Last check: 2007-10-19)
		The mid-oceanic ridges are centres of sea floor spreading where new crust is formed as lava wells up to the surface, in-so-doing pushing the crust on either side further apart, thus causing the continents to move.
		The oceanic plate is subducted back into the mantle, thus destroying oceanic crust, to balance the crust being produced at the mid oceanic ridges.
		As the oceanic plate gets pushed down into the mantle, a vast ocean trench is formed by the drastic lowering of the sea bed.
	ds.dial.pipex.com /ritson/earth/plate (1797 words)

	Geology 1005 Divergent Plates Nipissing University
		Ridges are generally 1500 km wide, with peaks which rise up to 3 km.
		The ridge is not one continuous diverging fracture.
		All ridge crests are a zone of volcanic activity as that is where new crust is 'born'.
	www.nipissingu.ca /faculty/ingridb/Geology/divergent_plates.htm (1055 words)

	Untitled Document
		They confirm that everywhere the oceanic crust is younger than about 200,000,000 years and that the stratigraphic age determined by micropaleontology of the overlying oceanic sediments is close to the age of the oceanic crust calculated from the magnetic anomalies.
		The oceanic crust is younger than the Jurassic, the geologic age that began approximately 208 million years ago, and this method fails to define the history of drifting continents during earlier geologic periods.
		This boundary is usually marked by an oceanic deep, or trench, where the overriding plate scrapes off the upper crust of the lower plate to create a zone of highly deformed, largely sedimentary rock.
	jpdawson.com /pelgnet/pelchap3/Chap3.html (6730 words)

	Proving the theory (Site not responding. Last check: 2007-10-19)
		The ocean floors are spreading away from mid-oceanic ridges, indicating that the ocean floor is moving.
		The oldest rocks on the ocean floor are younger than 220 million years, while the oldest terrestrial rocks are about 4 billion years old, indicating that the ocean floor is recycled back into the Earth.
		Bands of seafloor rocks paralleling the mid-oceanic ridges carry a record of this alternating polarity.
	whyfiles.org /094quake/5.html (599 words)

	g05 Magnetic anomalies parallel to and mirrored across oceanic ridges
		Magnetic stripes (linear magnetic anomalies) in the rocks of the seafloor, parallel to and mirrored across ridge segments, are a record of the earth's magnetic field reversals.
		In 1966, Vine’s correlation of the linear magnetic anomaly pattern of Reykjanes ridge (flown-survey map) with the independently known Earth’s magnetic reversal history g05iii left no skeptics as to the correctness of the Vine-Matthews seafloor spreading hypothesis, and the reality of continental drift could no longer be denied.
		Linked to the mantle convection, the new seafloor (oceanic crust) across the crest of the ridge is tensionally stressed and from time to time is split to form a rift.
	geowords.com /histbooknetscape/g05.htm (1831 words)

	The Early Theory of Continental Drift--Geosci PS 1030
		Mid oceanic ridge is surrounded by magnetized bands from where new ocean floor has been forming.
		Oldest (deepest) sediments are younger near the mid oceanic ridges and older near the ocean margins
		Old oceanic crust is recycled at the oceanic trenches--convergent plate boundaries.
	faculty.weber.edu /bdattilo/shknbk/notes/wgnr.htm (242 words)

	145.121 (Site not responding. Last check: 2007-10-19)
		Both intrusion (solidification beneath the surface) and extrusion (solidification on the surface or in the air) of magma occurs in association with orogenesis, probably as the result of subduction.
		Magma is also extruded at the rifts along the mid-oceanic ridges, but most of the world's volcanoes are associated with converging plate margins and in particular with the ocean trenches.
		One explanation for the breaking of the lithosphere beneath a geosyncline to form a subduction zone is that the sagging of the geosyncline in response to its filling with sediment causes metamorphism of the deeper materials to denser minerals, causing 'foundering', further melting and the release of heat as minerals change phase.
	www.massey.ac.nz /~wwglobal/145121/Lectures/lecture15.htm (656 words)

	Mid-ocean ridges (Site not responding. Last check: 2007-10-19)
		This is a map of the major oceanic spreading centers.
		The lava produced at the spreading centers is basalt, and is usually abbreviated MORB (for Mid-Ocean Ridge Basalt).
		Mid-ocean ridges are also the locations of many earthquakes, however, they are shallow and generally of small magnitude.
	volcano.und.nodak.edu /vwdocs/vwlessons/volcano_types/spread.htm (189 words)

	COAST - Deep Ocean Basins - Oceanic Ridges - Mid-Atlantic Ridge
		Cracks perpendicular to the ridge are transform faults, planes along which portions of the plates slide horizontally past each other.
		The horizontal scale of these features is so extensive that if their height were shown at the same scale, the fracturing and faulting would not be apparent.
		When operating the movie showing the Mid-Atlantic Ridge you may adjust the vertical scale by moving the mouse up and down and can change your position by moving left or right.
	www.coast-nopp.org /visualization_modules/physical_chemical/basin_coastal_morphology/principal_features/deep_ocean/oceanic_ridges/mid_atlantic.html (139 words)

	Search Results for oceanic - Encyclopædia Britannica
		The Mid-Oceanic Ridge is a continuous medial rift system that spans the length of the North Atlantic, South Atlantic, Indian, and South Pacific oceans for a combined distance of more than 40,000 miles (64,372 kilometers).
		Erupting from the mid-oceanic ridges, basalts record the alternating polarity of the Earth's magnetic field.
		In addition there are oceanic ridges forming interconnected chains of mountains that extend into the three principal oceans—the Pacific, Atlantic,...
	www.britannica.com /search?query=oceanic&fuzzy=N&ct=eb&start=8&show=10 (1148 words)

	Geoscience - The Earth - Shaping the Earth - Plate Tectonic processes
		It is driven by upwelling magmas from mantle regions that drive the plates away on either side of the ridge.
		Because oceanic crust spreads away from the mid-oceanic ridges, the oldest oceanic floor is found at the ocean margins.
		In contrast to oceanic crust, continental crust has constantly formed throughout much of the Earth's history, with the oldest rocks from Greenland dating back to 4.2 billion years, and the oldest known mineral, a zircon from the Pilbara region of Western Australia dating at 4.5 billion years.
	www.austmus.gov.au /geoscience/earth/tectonics.htm (2405 words)

	Mid-Cretaceous (Site not responding. Last check: 2007-10-19)
		In the Mid-Cretaceous the Tethys Ocean was closing and the Alps began to form.
		Magmas erupted at oceanic ridges created new oceanic crust forcing the continental land masses apart.
		Ridge systems rose high above the old ocean depths and lifted the neighbouring deep ocean floors with them.
	palaeo.gly.bris.ac.uk /communication/Willson/midcret.html (282 words)

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