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Topic: Oceanic rift

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	Seafloor spreading - Wikipedia, the free encyclopedia
		When one of the rifts opens into the existing ocean, the rift system is flooded with seawater and becomes a new sea.
		The destruction of oceanic crust occurs at subduction zones where oceanic crust is forced under either continental crust or oceanic crust.
		Since the new oceanic basins are shallower than the old oceanic basins, the total capacity of the world's ocean basins decreases during times of active sea floor spreading.
	en.wikipedia.org /wiki/Seafloor_spreading (888 words)

	Search Encyclopedia.com
		rift valley rift valley, elongated depression, trough, or graben in the earth's crust, bounded on both sides by normal faults and occurring on the continents or under the oceans.
		Oceanic languages Oceanic languages, aboriginal languages spoken in the region known as Oceania.
		Oceanic art Oceanic art, works produced by the island peoples of the S and NW Pacific, including Melanesia (New Guinea and the islands to its north and east), Micronesia (Mariana, Caroline, Marshall, and Gilbert islands), and Polynesia (which includes the Hawaiian Islands, the Samoas, Tonga, New Zealand, and Easter Island).
	www.encyclopedia.com /searchpool.asp?target=Oceanic+rift (567 words)

	PACES Mission Statement (Site not responding. Last check: 2007-10-14)
		Models of continental break-up and the initiation of oceanic rift segmentation predict profound differences in 3-D geometry of the crust and upper mantle during break-up, but existing data are inadequate to distinguish between these models.
		Both geophysical and geological data from the ‘near break-up’ transitional rift (2B) (predicted structure, in part after Ebinger and Casey, 2001) show a very narrow zone of strain and magma injection that is similar to 2A.
		In the oceanic setting, along-axis mantle flow patterns preserved in olivine crystal alignments predicted by the periodic upwelling models are matched by observations of mantle anisotropy (Blackman & Kendall 1997), but there are few data from continental rifts adequate to assess 3-D upper mantle flow.
	paces.geo.utep.edu /RESEARCH/EAGLE/mission.shtml (927 words)

	The EXPANDING EARTH - Geology
		On that side is new oceanic crust with high heat flux and repeated horsts and grabens, in contrast with the eastern side characterized by seismic quiet and little disturbed sediment.
		The north-west Pacific's oceanic crust is largely of Jurassic age and hence, in an expansion interpretation, was extruded from the mantle at a Jurassic palaeo-radius, and a correspondingly higher surface curvature (quantitative modelling, of pre-Jurassic Earth indicates palaeo-radius ~50 % present).
		Oceanic crust forms directly from to the top of the mantle being exposed at mid ocean ridges as Earths' waxing internal expansion pulls the crust apart at submerged rifting fissures commonly called mid-ocean-ridges.
	www.geocities.com /CapeCanaveral/Launchpad/8098/1.htm (13217 words)

	Oceanic ridge - Wikipedia, the free encyclopedia
		An oceanic ridge is an underwater mountain range, usually formed by plate tectonics.
		They are geologically active, with new magma constantly emerging onto the ocean floor through a gap called a rift in the earth's crust.
		The rocks making up the sea floor are usually younger near the centre of the ridge and the older ones located farther away from the rift.
	en.wikipedia.org /wiki/Oceanic_ridge (137 words)

	Geosphere Background
		The newest oceanic crust is found within and adjacent to the spreading center; progressively older ocean crust is found with increasing distance from the divergent boundary.
		Convergent zones involving oceanic crust are marked by an arcuate, linear trench where the subducting plate bends downward, and an arcuate, linear chain of volcanoes behind the trench, on the overriding plate.
		This is the oldest oceanic crust in the world, and the area is a maze of trenches, island arcs, shallow sedimentary basins, and continental crust fragments.
	www.math.montana.edu /~nmp/materials/ess/geosphere/background (6418 words)

	Understanding plate motions [This Dynamic Earth, USGS]
		As with oceanic-continental convergence, when two oceanic plates converge, one is usually subducted under the other, and in the process a trench is formed.
		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).
		Oceanic fracture zones are ocean-floor valleys that horizontally offset spreading ridges; some of these zones are hundreds to thousands of kilometers long and as much as 8 km deep.
	pubs.usgs.gov /publications/text/understanding.html (2502 words)

	Plate Tectonics (Site not responding. Last check: 2007-10-14)
		The fastest-moving plates are the oceanic plates, with the Cocos plate having the highest velocity at 8.6 cm per year.
		Because the oceanic plate is being destroyed, the area along an edge of a plate where subduction occurs - the subduction zone - is known as a 'destructive plate margin'.
		Here, three volcanically active rifts - the Rift Valley, the Red Sea, and the Gulf of Aden - radiate outwards from where a hot spot is believed to impinge on the base of the continental crust under an extremely hot desert in Ethiopia.
	www.bbm.me.uk /Portsdown/PH_063_PlateTec.htm (2675 words)

	Islamset - Introduction: The Faulted Earth, The Seat Set on Fire, The Mountains Created As Pegs (Or Pickets), The ... (Site not responding. Last check: 2007-10-14)
		Both the Red Sea and the Gulf of California throughs (which are extensions of oceanic rifts) are currently widening at the rate of 3 cm/year in the former and 6 cm/year in the latter case.
		The age of the oldest existing oceanic crust does not exceed the Mesozoic era (about 200 million years old), and is currently being consumed at the convergent edges of the plates with rates almost equivalent to the rate of producing new oceanic crust at the mid-oceanic ridges.
		Such rifts run for terms of thousands of kilometers across the globe, in all directions, to a depth of 65-150 km where it connects the seabed with the extremely hot plastic, semi - molten (asthenosphere) and hence cause such seas to be physically set on fire.
	www.islamset.com /sc/geology/introduction.html (7065 words)

	DISCUSSION (Site not responding. Last check: 2007-10-14)
		The syn- and postbreakup volcanics were envisaged to have accumulated, fractionated, and extruded within the new oceanic rift zone at the outer edge of the continent.
		Magmas that bypass the center of a rift zone and are erupted on older crust are known from other areas including oceanic ridges, and they tend to be compositionally different from those being erupted at the rift axis.
		Outside the continental edge, the igneous part of the oceanic crust is constantly ~18 km thick (at 3-21-km depth) and consists of three units (3, 5, and 6 in Figure 8).
	www.ga.gov.au /odp/publications/163_SR/chap_07/ch7_htm6.htm (3910 words)

	d09 Rift valleys and triple junctions (Site not responding. Last check: 2007-10-14)
		Divergent plate boundaries within oceanic areas are identified as the crest of wide oceanic rise-ridge mountain systems with innumerable abyssal hills, the crests of which, for long distances, parallel the ridge axis (Figure d09ii).
		A pronounced rift valley at the ridge (axial-valley) is the most characteristic topographic feature of the boundary between divergent lithospheric plates, which are separating at slow (less than) to intermediate rates (some 6 cm per year).
		This results in three rift valleys and associated ridges, which radiate with a T or a Y map pattern from the common point (triple junction).
	geowords.com /histbooknetscape/d09.htm (467 words)

	Broadband Systems (Site not responding. Last check: 2007-10-14)
		Continental and oceanic settings show many similarities in structure and process, but have two major differences: new lithosphere with dominant olivine mineralogy is created and then stretched at spreading centres, whereas ancient, thick continental crust and upper mantle of highly variable composition is stretched in continental rifts.
		Active and ancient continental rifts and passive margins worldwide are segmented along-axis into discrete basins, indicating that segmentation is a fundamental response of the continental lithosphere to rifting processes.
		By analogy to oceanic rifts, magmatic segmentation models predict periodic upwellings of asthenosphere at ~100 km intervals along the rift axis which provide melt for crustal magma chambers and fissural eruptions.
	www.le.ac.uk /seis-uk/scientific_rationale2.htm (8415 words)

	Classroom@Sea: The Carlsberg Ridge Cruise (Site not responding. Last check: 2007-10-14)
		Oceanic constructive margins are characterised by a central submarine spreading ridge where new oceanic crust is injected into the central rift.
		Oceanic constructive margins represent the next evolutionary stage on from continental rift systems such as the East African Rift Valley and Red Sea area.
		These stripes can be correlated with the age bands of the oceanic crust, and the banding pattern is symmetrical either side of the spreading line.
	www.soc.soton.ac.uk /CHD/classroom%40sea/carlsberg/science/oceanic_constr.html (977 words)

	CHAPTER 10 - STUDY GUIDE
		Oceanic crust is relatively young age and is being created even today at mid-oceanic rift zones.
		On average of oceanic crust is 7 km thick and mainly composed of the igneous rock basalt.
		Oceanic crust is returned to the mantle at the subduction zones found along the continental margins.
	www.physicalgeography.net /fundamentals/studyguide_ch10.html (6819 words)

	Untitled
		The second ultramafic in the tectonic rock cycle is the sterile fractionated residue generated by fractionation of ophiolite layers 1 and 2 at the subduction zone.
		Tectonically, this phase of the tectonic rock cycle has shifted from a divergent plate boundary where oceanic lithosphere is generated to a convergent plate boundary where oceanic lithosphere is destroyed.
		As the oceanic slab descends and fractionally melts, the unmelted ultramafic residue remains in the mantle or continues to descend with the subducting oceanic lithosphere.
	csmres.jmu.edu /geollab/Fichter/Wilson/Rkcytex2.html (2556 words)

	abstract (Site not responding. Last check: 2007-10-14)
		The high relief of the SWIR rift flanks, containing tilted seafloor of the other two ridges, may be an isostatic response of the lithosphere to the deep valley produced by this rifting.
		In particular, the deepening and widening of the valley away from the triple junction is attributed to the competing effects of tectonic thinning and lithospheric cooling.
		This rate of widening of the deformation zone may therefore support lithospheric necking models for oceanic rift valleys, if the width and depth of the deforming lithosphere are related in a simple manner.
	www.ocean.cf.ac.uk /people/neil/cv/iotj-dd.html (313 words)

	Geological Society - News - Geoscience at the BA: EAGLE eyes Afar horizon
		Says Maguire: “The Kenya Rift provides an example of the very early stages in the break-up of a continental rift, in which, at least in the south, the first order structure is controlled by faulting.
		Current models of continental break-up and the initation of oceanic rift segmentation predict profound differences in 3-D geometry of the crust and upper mantle during break-up, but existing data are inadequate to distinguish between these models.
		“EAGLE is to study the transition from continental to oceanic rifting beneath the Northern Ethiopian Rift and the as yet poorly understood processes associated with lithospheric break-up; for example, underplating and lower crustal intrusion, basement control on the rifting process, the formation of thick igneous crust beneath resultant volcanic margins, mantle layering.
	www.geolsoc.org.uk /template.cfm?name=BA2002F (1236 words)

	[No title]
		Elsewhere, earthquakes occur along a well-defined rift zone, and focal mechanisms reveal normal faulting with north-south T axes and depths less than 10 km.
		In this region just landward from the rift tip the highest extension rates are expected (40 mm/yr) and strain is likely to be localized on a single system of normal faults.
		Because shallow dips for normal faults are seen near the rift tip, but not elsewhere along strike, high strain rates may be an important factor in allowing normal faults to slip at unusually shallow dips.
	www.agu.org /pubs/abs/jb/97JB00787/97JB00787.html (359 words)

	Geology 1005 Divergent Plates Nipissing University
		Rifting allows mantle material to rise to the surface and cool where it becomes the youngest rock on earth.
		In fact, rifting of continents leads to the development of new ocean basins.
		Rift mountains are not formed by folding as are continental mountains.
	www.nipissingu.ca /faculty/ingridb/Geology/divergent_plates.htm (1055 words)

	Southeastern Brazilian continental margin (Site not responding. Last check: 2007-10-14)
		The Congo and Cabinda margins of west Africa and the Camamu-Almada margin of east Brazil are characterised by a common tripartite rift history; Berriasian to Hauterivian, Hauterivian to mid Barremian, and late Barremian to early Aptian.
		Early, depth-independent, broadly-distributed brittle deformation (rift phases I & II) was progressively replaced by depth-dependent deformation in which rifting was dominated by plastic thinning of the lower crust and lithospheric mantle (rift phase III).
		By analogy with the west African margin and dating from ostracod zonations, the non-marine component of the Lagoa Feia Formation correlates with rift phase II while the "transitional" component is associated with rift phase III, the plastic thinning of the lower crust and lithospheric mantle.
	www.ldeo.columbia.edu /karner/descriptions/ebrazil.word.html (520 words)

	Oceanic rift (Site not responding. Last check: 2007-10-14)
		In plate tectonics, a divergent boundary(divergent fault boundary or divergent plate boundary) is a linear feature that exists betweentwo tectonic plates where the plates are moving away from each other.These areas can form in the middle of continents but soon (in a geologic time sense) form ocean basins.
		Therefore most divergentplate boundaries exist between oceanic plates and are often called oceanicrifts as a result.
		It is thought that convection currents in the Earth 's mantle rise to the base of the lithosphere where the divergent plate boundary exists.
	www.therfcc.org /oceanic-rift-74051.html (165 words)

	Woodlark Basin Bibliography
		Goodliffe, A.M., The rifting of continental and oceanic lithosphere: observations from the Woodlark Basin [Ph.D. thesis], Univ. Hawaii, Honolulu, HI, 1998.
		Fantozzi, P.L, Transition from continental to oceanic rifting in the Gulf of Aden: structural evidence from field mapping in Somalia and Yemen, Tectonophysics, 259, 285-311, 1996.
		Dyment, J., and J. Arkani-Hamed, Spreading-rate-dependent magnetization of the oceanic lithosphere inferred from the anomalous skewness of marine magnetic anomalies, Geophys.
	www.geo.ua.edu:16080 /AMG/OldMargins/WoodlarkBibliography.html (5506 words)

	[tblSetting] - GeoReference Online Ltd.
		Oceanic basins behind intraoceanic magmatic arcs (inc interarc basins between active and remnant arcs) and cont.
		Incipient oceanic basins floored by new oceanic crust and flanked by young rifted continental margins
		Rifts within continental crust, commonly associated with bimodal volcanism.
	www.georeferenceonline.com /MineMatch/images/tblSetting.htm (1934 words)

	Oceanic trench See also subducting slab Challenger Deep Mariana Trench Cayman Trench Atacama Trench Oceanic ridge plate ... (Site not responding. Last check: 2007-10-14)
		The oceanic trenches are several hundred kilometres long but narrow topographic depressions of the sea floor.
		A trench marks the position at which the flexed, subducting slab begins to go under, on the convex side and between 50 and 250 km from a volcanic arc.
		Oceanic trenches typically extend 3 to 4km (1.9-2.5 mi) below the level of the surrounding oceanic floor.
	en.powerwissen.com /mPbxaskkiyaSc8xb1uRJhQ%3D%3D_Oceanic_trench.html (179 words)

	[Islam-Online- Science, Ideas & Technology]
		Both the Red Sea and the Gulf of California troughs (which are extensions of oceanic rifts) are currently widening at the rates of 3cm/year and 6cm/year respectively.
		These lithospheric faults are a globe-encircling system of prominent rift zones (65-150 km deep and tens of thousand km long) along which lithospheric plates are displaced with respect to one another divergently, convergently or sliding past each other.
		These are associated with intra-cratonic, deep rift systems that traverse the whole thickness of the lithosphere, and communicate with the asthenosphere, and hence are currently fragmenting the existing continents into smaller landmasses.
	islamonline.net /iol-english/dowalia/techng-2000-August-22/techng3.asp (1233 words)

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