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Topic: Divergent plate boundaries

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Subduction zone

	MSN Encarta - Print Preview - Plate Tectonics
		Divergent boundaries on land cause rifting, in which broad areas of land are uplifted, or moved upward.
		Early in the plate tectonic revolution, geologists proposed that transform faults were a new class of fault because they “transformed” plate motions from one plate boundary to another.
		As a transform plate boundary cuts perpendicularly across the edges of the continental crust near the borders of the continental and oceanic crust, the result is a system such as the San Andreas transform fault system in California.
	encarta.msn.com /text_761554623___7/Plate_Tectonics.html (1481 words)

	Plate Tectonic Theory: Plates and Interplate Relationships
		It might be possible for a plate to be a continent alone, but for this to occur all edges of the continent would have to be a plate boundary (very rare, perhaps not practically possible).
		Two divergent margins (plate boundaries) are present in the cross section: one labeled as such to the right of the continental craton, and the other on the left side.
		Divergent plate boundaries always create new ocean floor (that is, new mafic oceanic lithosphere, called the ophiolite suite) when magma oozes into the crack as plates separate.
	csmres.jmu.edu /geollab/Fichter/PlateTect/plates.html (1238 words)

	Plate Tectonics (Site not responding. Last check: 2007-10-08)
		Plate Tectonics is a theory developed in the late 1960s, to explain how the outer layers of the Earth move and deform.
		Plate tectonics has proven to be so useful that it can predict geologic events and explain almost all aspects of what we see on the Earth.
		When a plate of dense oceanic lithosphere moving in one direction collides with a plate moving in the opposite direction, one of the plates subducts beneath the other.
	earthsci.org /teacher/basicgeol/platec/platec.html (1838 words)

	Plate Tectonic Theory: Plates and Interplate Relationships
		A plate may be an ocean basin alone, or a continent alone, or a combination of ocean basin+continent (common).
		It is possible a plate could be a continent alone, but for this to occur all edges of the continent would have to be a plate boundary (very rare, perhaps not practically possible).
		Divergent plate boundaries always create new ocean floor (that is, new oceanic lithosphere, called the ophiolite suite).
	csmres.jmu.edu /geollab/vageol/vahist/plates.html (917 words)

	Understanding plate motions [This Dynamic Earth, USGS]
		Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.
		Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle.
		Land on the west side of the fault zone (on the Pacific Plate) is moving in a northwesterly direction relative to the land on the east side of the fault zone (on the North American Plate).
	pubs.usgs.gov /publications/text/understanding.html (2502 words)

	The Terrible Power of Earthquakes (Site not responding. Last check: 2007-10-08)
		Divergent plate boundaries are mostly on ocean floors.
		At other convergent plate boundaries, the edge of the descending plate, all its cover of sediment, and even pieces from the edge of the overriding plate disappear beneath the overriding plate.
		At boundaries where plates carrying continents collide, layers of rock in the overriding plate crumple and fold like a tablecloth that is pushed across a table.
	www.worldbook.com /features/earthquakes/html/where_interactions.html (873 words)

	Plate boundaries (Site not responding. Last check: 2007-10-08)
		At convergent boundaries, there is a collision between two plates.
		Where the plates meet, the cold, denser plate sinks under the warmer, less dense plate in a process called subduction.
		This plate, which includes the western edge of California, is moving northwestward relative to the North American plate.
	www.isgs.uiuc.edu /servs/pubs/geobits-pub/geobit10/plt.htm (345 words)

	1929 Wall Street Crash: Genie 4 Custom Term Papers
		At divergent boundaries, two plates move apart from each other and the space is filled with new crustal material sourced from molten magma that forms below the earths crust.
		The beginning of divergent boundaries is thought to be associated with the phenomenon known as hotspots.
		The Pacific and Cocos plates are the fastest moving and the Arabian and southern African plates are slowest.
	www.termpapergenie.com /platetectonics.html (845 words)

	Plate boundaries
		Plate boundaries are found at the edge of the lithospheric plates and are of three types,
		Divergent boundaries are responsible in part for driving the motion of the plates.
		Another example of a transform boundary is seen at the mid-ocean ridges, where the spreading centers are offset by transform faults anywhere from a few meters to several kilometers in length.
	scign.jpl.nasa.gov /learn/plate4.htm (940 words)

	Types of plate boundaries (from Earth) -- Encyclopædia Britannica (Site not responding. Last check: 2007-10-08)
		Plates move in opposite directions along the same line at divergent plate boundaries.
		These boundaries are located at mid-oceanic ridges (spreading ridges) such as the Mid-Atlantic Ridge and the East Pacific Rise.
		These plates move relative to each other and interact at their boundaries, where they diverge, converge, or slip relatively harmlessly past one another.
	www.britannica.com /eb/article-9288 (1055 words)

	Plate Tectonics : Plate Boundaries
		As the giant plates move, diverging [pulling apart] or converging [coming together] along their borders, tremendous energies are unleashed resulting in tremors that transform Earth’s surface.
		While all the plates appear to be moving at different relative speeds and independently of each other, the whole jigsaw puzzle of plates is interconnected.
		The San Andreas fault zone in California is a transform fault that connects the East Pacific Rise, a divergent boundary to the south, with the South Gorda -- Juan de Fuca -- Explorer Ridge, another divergent boundary to the north.
	www.platetectonics.com /book/page_5.asp (831 words)

	An Introduction to Plate Tectonics
		Plate movement takes place laterally away from the plate boundary, which is normall marked by a rise or a ridge.
		The rate at which each plate moves apart from a divergent margin varies from less than 50 mm per year to over 90 mm per year and can be determined from the pattern of magnetic anomalies either side of a spreading ridge.
		As one of the plates is subducted beneath the other it begins to melt at a depth of between 90 and 150 km and the resulting magma rises to the surface above the subduction zone to form a chain or arc of volcanoes.
	www.hartrao.ac.za /geodesy/tectonics.html (2104 words)

	Earth Floor: Plate Tectonics
		Plates only move a few centimeters each year, so collisions are very slow and last millions of years.
		Looking at this drawing of two plates colliding is like looking at a single frame in a slow-motion movie of two cars crashing into each other.
		The edge of the continental plate in the drawing has folded into a huge mountain range, while the edge of the oceanic plate has bent downward and dug deep into the Earth.
	www.cotf.edu /ete/modules/msese/earthsysflr/plates2.html (468 words)

	Plate Boundaries (Site not responding. Last check: 2007-10-08)
		Convergent boundaries come in three varieties depending upon the type of lithosphere that is juxtaposed across a subduction zone.
		Hawaiian Islands form a linear chain of islands but they are located in the center of the Pacific plate and were not formed by subduction along a plate boundary.
		Plates on either side of a transform boundary slide past each other without either plate being consumed and without a gap opening between the plates.
	enterprise.cc.uakron.edu /geology/natscigeo/Lectures/ptectonics/pboundary.htm (1166 words)

	Earth Floor: Plate Tectonics
		As the plates separate along the boundary, the block between the faults cracks and drops down into the soft, plastic interior (the asthenosphere).
		Where a divergent boundary crosses the land, the rift valleys which form are typically 30 to 50 kilometers wide.
		Where a divergent boundary crosses the ocean floor, the rift valley is much narrower, only a kilometer or less across, and it runs along the top of a midoceanic ridge.
	www.cotf.edu /ete/modules/msese/earthsysflr/plates3.html (259 words)

	Geology 1005 Divergent Plates Nipissing University
		Divergence occurs predominantly along the mid-oceanic ridges, and to a lesser extent within continental crust.
		Most divergent plate boundaries occur in ocean basins and underwater.
		The island experiences fissure-type volcanoes which are common to divergent boundaries.
	www.nipissingu.ca /faculty/ingridb/Geology/divergent_plates.htm (1055 words)

	Major Tectonic Plates of the World (Site not responding. Last check: 2007-10-08)
		Where an oceanic plate collides with a continental plate, the oceanic plate tips down and slides beneath the continental plate forming a deep ocean trench (long, narrow, deep basin.) An example of this type of movement, called subduction, occurs at the boundary between the oceanic Nazca Plate and the continental South American Plate.
		Where plates diverge, hot, molten rock rises and cools adding new material to the edges of the oceanic plates.
		Plate tectonics, the branch of science that deals with the process by which rigid plates are moved across hot molten material, has helped to explain much in global-scale geology including the formation of mountains, and the distribution of earthquakes and volcanoes.
	geology.er.usgs.gov /eastern/plates.html (245 words)

	d08 Divergent plate boundaries (Site not responding. Last check: 2007-10-08)
		The volcanism that occurs at mid-oceanic ridges is the eruption of fissure basalts.
		In the plate tectonics model, these lavas originate from the partial melting of the asthenosphere that, to maintain isostasy, rises between diverging lithosphere plates The melting occurs because rock is a poor conductor of heat and it mostly retains the temperature it had at depth.
		These basalts accumulate on the diverging lithosphere plate edges and are moved away to either side of the ridge as oceanic crust.
	geowords.com /histbooknetscape/d08.htm (1598 words)

	OptIPuter Outreach
		These are zones where two plates move away from each other, allowing magma from the mantle to rise up and solidify as new crust.
		Magmas that form island arcs are produced by the partial melting of the descending plate and/or theoverlying oceanic lithosphere.
		The zone between two plates sliding horizontally past one another is called a transform-fault boundary, or simply a transform boundary.
	education.sdsc.edu /optiputer/teachers/platemovement.html (958 words)

	Plate Tectonics: Divergent Plate Boundaries
		Narrow oceans represent youthful divergent boundaries and wide oceans are indications of a long-lived ocean basin.
		Divergent plate boundary: Where plates move apart, e.g., separation of plates along oceanic ridges.
		Convergent plate boundary: Where plates converge, e.g., collision between plates adjacent to trench, one plate over-rides another.
	www.mhhe.com /earthsci/geology/mcconnell/pte/dpb.htm (553 words)

	esm_hamblin_eds_10\|Divergent Plate Boundaries\|Major Concepts
		Divergent plate boundaries are zones where lithospheric plates move apart from one another.
		An oceanic ridge marks divergent plate boundaries in the ocean basins.
		Oceanic crust is generated at divergent plate boundaries and is composed of four major layers: (a) deep marine sediment, (b) pillow basalts, (c) sheeted dikes, and (d) gabbro.
	wps.prenhall.com /esm_hamblin_eds_10/0,8010,838203-,00.html (293 words)

	USGS Geology in the Parks (Site not responding. Last check: 2007-10-08)
		The plates can push against each other, producing a convergent plate boundary, the plates can move apart, forming a divergent plate boundary, or the plates can slip past each other side to side, which geologists call transform plate boundaries.
		The fate of the colliding plates depends mostly on what type of lithosphere they are made of.
		This type of boundary separates the North American plate from the Pacific plate along the San Andreas fault, a famous transform plate boundary that's responsible for many of California's earthquakes.
	wrgis.wr.usgs.gov /docs/usgsnps/pltec/pltec3.html (305 words)

	UGA GEOL 1121 - Railsback (Site not responding. Last check: 2007-10-08)
		Plate Tectonic theory assumes that rigid pieces of oceanic, or oceanic plus continental, lithosphere ("plates") move across the earth surface over a more ductile asthenosphere.
		Where plates move apart at divergent plate boundaries, new lithosphere must form.
		Where plates come together at convergent plate boundaries, lithosphere must be destroyed.
	www.gly.uga.edu /railsback/1121Lxr02.html (260 words)

	Earth Floor: Plate Tectonics
		The plates are all moving in different directions and at different speeds (from 2 cm to 10 cm per year--about the speed at which your fingernails grow) in relationship to each other.
		The plates are moving around like cars in a demolition derby, which means they sometimes crash together, pull apart, or sideswipe each other.
		The place where the two plates meet is called a plate boundary.
	www.cotf.edu /ete/modules/msese/earthsysflr/plates1.html (198 words)

	Introduction to Plate Tectonics (Site not responding. Last check: 2007-10-08)
		The ways that plates interact depend on their relative motion and whether oceanic or continental crust is at the edge of the lithospheric plate.
		The mid-Atlantic Ridge, a topographically high area near the middle of the Atlantic Ocean, is an example of a divergent plate boundary.
		The west margin of the South American continent, where the oceanic Nazca Plate is pushed toward and beneath the continental portion of the South American Plate, is an example of a convergent plate boundary.
	volcano.und.nodak.edu /vwdocs/vwlessons/plate_tectonics/part13.html (156 words)

	Plate Tectonics
		List the basic types of plate boundaries (divergent, convergent, transform) and describe the relative motions of each.
		Know the history of the development of the theory of Plate Tectonics, and recognize the contributions of various geoscientists (Alfred Wegener, Harry Hess, Fred Vine and D. Matthews).
		Identify the various features associated with the basic types of plate boundaries (rift valley, subduction zone, deep sea trench, Benioff zone, etc.).
	www.gpc.edu /~pgore/geology/geo101/platetec.htm (637 words)

	3. Plate Tectonics
		the denser plate (normally the oceanic plate – basalt) is being "subducted" (pushed) under the lighter plate (normally the continental plate – granite), causing deep ocean trenches at the continental margins.
		Divergent plate boundaries occur where plates appear to be moving apart - for example along mid- oceanic ridges or along the Great Rift Valley in East Africa.
		Thus, many regions which are vulnerable to earthquakes (plate boundaries) have instituted building codes that are much more stringent than those in places believed to be less at risk.
	www.rossway.net /20503.htm (2137 words)

	Convergent Plate Boundaries (Site not responding. Last check: 2007-10-08)
		At some plate margins, the density of cooler lithospheric plate is sufficiently greater than that of the hot, plastic asthenosphere beneath, that the plate is sinking beneath the adjacent plate and back into the hotter, deeper regions of the mantle.
		The convergent plate boundaries that occur on continents are the collisional mountain belts.
		This inclined zone of seismic activity along convergent plate boundaries is known as the benioff zone.
	www.gly.fsu.edu /~odom/1000/tectonics/cpb.html (746 words)

	Plate Tectonics Boundaries
		Use the plate tectonics theory to explain features of the earthís surface and geological phenomena and describe evidence for the plate tectonics theory.
		To have students see and experience what happens at each type of plate boundary and why there are certain types of geographic features on the surface of the Earth whether under water or on land.
		The Theory of Plate Tectonics states that the Earth’s crust is composed of major pieces or plates.
	www.inghamisd.org /~goals2k/lessons/sciencelesson/tippin3.html (1338 words)

	GeoTopics @ GeoNet
		The are two types of tectonic plates - continental plates and oceanic plates.
		The point where two or more plates meet is known as a plate boundary.
		Conservative plate boundaries occur when two plates slide past each other.
	www.bennett.karoo.net /topics/platetec.html (250 words)

	PlateTectonics
		The study of plate tectonics is the study of how these lithospheric plates form, move about, and are destroyed.
		It melts at divergent plate boundaries to form a mafic magma, which becomes basalt at the surface, and gabbro at depth.
		Earthquakes are shallow at divergent and transform plate boundaries, where the crust is thin and the asthenosphere rises to near the Earth's surface.
	www-class.unl.edu /geol101i/11a_plates.htm (4561 words)

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