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Topic: Midocean ridge

In the News (Thu 20 Jun 19)

  Midocean Ridges
The crust and upper mantle are hot at the midocean ridge because of the heat carried with mantle as it rises under the ridge.
So, at the ridge, the zone of partial melting is at a shallow depth beneath the crust, and away from the ridge, the depth to the top of the zone of partial melting (the top of the asthenosphere) is deeper because the rocks have cooled.
Seawater that saturates the fractures near the midocean ridge are heated by the presence of magma and hot newly-formed rocks.
myweb.cwpost.liu.edu /vdivener/notes/MOR.htm   (1078 words)

 History Channel Search Results
The boundaries between the plates are of three types: midocean ridges, where plates diverge; deep-sea trenches, or “subduction” zones, where two plates converge and one dives under the other; and transform, or “strike-slip,” faults, where plates slide past each other.
Another 19th-century discovery was that there was a midocean ridge in the Atlantic; by the 1920s scientists had concluded that this ridge was continuous almost all the way around the world.
They noticed that the crest of the midocean ridge is in the form of a rift, or cleft, a few kilometers across, that coincides with the ridge center.
www.historychannel.com /encyclopedia/article.jsp?link=FWNE.fw..pl094800.a   (1743 words)

 d08 Divergent plate boundaries
For the historical reason of its description as the "midocean ridge system," continuations of it are similarly referred to even when they are not centrally located in other oceanic areas.
The volcanism that occurs at mid-oceanic ridges is the eruption of fissure basalts.
However, the amount of basaltic lava erupted at the ridge is less constant than is the rate of sea floor spreading from the ridge, which indicates seafloor crust comes to be at a global rate of about 21 cubic kilometers per year.
geowords.com /histbooknetscape/d08.htm   (1598 words)

 When the Earth Moves - Insights from the Ocean
The Lamont researchers also found that the crest of the ridge system is virtually bare of sediments, as compared with the thick layer of sediment on the plains near the continental margins, which can reach a thickness of several miles.
The soundings revealed the entire midocean ridge system to be 37,200 miles in length, long enough to circle the equator one and one-half times.
Where the currents rise to the surface, molten material oozes out, building up the midocean ridges and forming new oceanic crust; as magma continues to flow, older seafloor is carried away in either direction from the ridge by mantle convection.
www.beyonddiscovery.org /content/view.page.asp?I=232   (1052 words)

 Lucky Strike Smokers Are Different
Moreover, because the ridges are under a few thousand meters of water, and therefore under a few hundred bars of pressure, the volatile chemicals that come out of volcanoes—things like water, carbon dioxide, noble gases, methane, hydrogen, and hydrogen sulfide—actually stay dissolved in the glass that forms the rims of the basalt pillows.
Although most midocean ridge rocks are about the same, because the mantle source is rather homogeneous and the spreading process is everywhere similar, exceptions occur near hot spots—volcanic sources that are fixed in one place while the earth’s plates move over them.
The depth to the ridge axis, in turn, reflects the density of the underlying rock column—since crust is less dense than mantle, areas of thick crust stand higher, a principle called isostasy, which is just Archimedes’ principle applied to the earth’s rigid upper layers floating on the ductile interior.
pr.caltech.edu /periodicals/EandS/articles/LXV3/asimow.html   (4578 words)

 300 Plate Tectonics
Magnetic studies across the midocean ridges showed that there were mirror-image magnetic zones or stripes in the rocks on the bottom of the ocean and that these zones were parallel to the ridges and were of alternating strong and weak magnetism.
Because the rocks in the first weakly magnetic zone (reversed polarity) away from the midocean ridge could not have formed under present conditions of normal polarity, they must have formed during the most recent period of reversed polarity and, therefore, must be older than the rocks along the midocean ridge.
As distance from the midocean ridge increases, volcanic rocks should alternate from normal to reversed in magnetic polarity.
www.csun.edu /~khurst/ES300/Fritche/300platetec.html   (1350 words)

 Research Highlights Juan de Fuca Ridge 2000
The discovery of a midocean ridge (MOR) spreading center off the northwest coast of North America was first postulated in the late 1950's with the discovery of an undersea ridge and valley terrain.
Gorda ridge spreads at the same rate as the JDFR and is extremely seismically active while the JDFR is aseismic.
Endeavour Ridge was imaged by MCS in 1985 and a narrow (1 km) axial reflector was found at about 2.5 km depth beneath the ridge axis [Rohr et al., 1988].
deeptow.whoi.edu /jdf.html   (2413 words)

 When the Earth Moves - Text View
To explain the ridges, Henry Hess theorized that the seafloor was slowly spreading away from the ridges, driven by convection currents in the mantle (see Insights from the Ocean).
This new view suggested that active deformation is concentrated at the ridges and along their connecting faults and that the rest of the ocean crust simply drifts along, unbroken.
Sykes found that oceanic earthquakes were, indeed, concentrated along the mid-ocean ridges and their connecting faults, and that the interiors of the oceanic "plates" were nearly aseismic, or earthquake-free.
www.beyonddiscovery.org /content/view.txt.asp?a=229   (4728 words)

 Uncharted Territory: Science News Online, April 1, 2006   (Site not responding. Last check: 2007-10-23)
At fast-spreading ridges, such as the East Pacific Rise, the plates move apart at a rate of 100 to 200 millimeters per year and are rapidly supplied with hot magma.
These ridges are narrow with a tentlike shape, formed by sheets of lava flowing from a hot, buoyant central peak.
Discovery of abundant hydrothermal venting on the ultraslow-spreading Gakkel ridge in the Arctic Ocean.
www.sciencenews.org /articles/20060401/bob9.asp   (2475 words)

 Airguns gauge undersea volcanoes.(Geology) - USA Today (Magazine) - HighBeam Research   (Site not responding. Last check: 2007-10-23)
A mechanism that counters established thinking on how the rate at which tectonic plates separate along midocean ridges controls processes such as heat transfer in geologic materials, energy circulation, and even biological production has been revealed by a Georgia Institute of Technology, Atlanta, study.
The research also has pioneered a new seismic technique--simultaneously shooting an array of 20 airguns to generate sound--for studying the Earth's mantle, the layer beneath the 10- to 40-kilometer-deep crust on the seafloor.
"Midocean ridges produce most of the volcanism on the Earth, releasing a lot of heat--in some places enough to support large biological communities on the seafloor," notes Daniel Lizarralde, assistant professor in the School of Earth and Atmospheric Sciences.
www.highbeam.com /library/docfree.asp?DOCID=1G1:133049668&ctrlInfo=Round19:Mode19b:DocG:Result&ao=   (542 words)

 Research: Deep sea basalt may help reveal volcanoes’ impact on climate
The area, known as the Siqueiros Transform fault, a deep part of the midocean ridge, was known to experience underwater eruptions, which is why the scientists chose it for their investigation.
This is important, because the midocean ridge is a mammoth, 40,000-mile long mountain where 85 percent of the world's volcanic activity occurs.
As a result, if the basalts Alvin returned to the surface are typical of other midocean ridge basalts, it could help determine the rate at which Earth's below-ground carbon dioxide is supplied to the atmosphere through volcanoes, he said.
www.eurekalert.org /pub_releases/2002-10/uof-rds100302.php   (800 words)

 [No title]   (Site not responding. Last check: 2007-10-23)
Nansen Basin (Cenozoic) (Laptev Sea) Underlies the Eurasia Basin of the Arctic Ocean between the Mid-Arctic ridge, the actively spreading boundary between the Eurasia and North American Plates in the Arctic Ocean, and the continental slope of the Barents Sea.
The Nansen and Amundsen basins are separated by the Gakkel (Arctic Midocean) Ridge of late Paleocene to Quaternary age that is the spreading axis and modern boundary of the Eurasian and North American plates.
The Gakkel (Arctic Midocean) Ridge is deep compared to other midocean ridges; in some localities over 3 km deep, possibly indicating a passive nature.
pubs.usgs.gov /of/1999/of99-422/norpac/data/terranes/nor_pac/explanat/terranes/NAN.txt   (314 words)

 12-Midocean Ridges
Research by Americans with new and improved shipboard depth sounding instruments during and after World War Two quickly extended knowledge of the midocean ridges so that by the early-1960's they were known to extend for almost ~65,000 kilometers (~40,000 km) throughout all oceans.
The full extent of ridge volcanism and "fl smoker" vents discharging very hot water and minerals was not known until 1977, and new details of the ridges and vents are being discovered on a regular basis.
The midocean ridges are, in effect, the "enabling mechanism" that permits controlled expansion of the planet.
www.expanding-earth.org /page_12.htm   (1033 words)

The discovery of the midocean ridge systems, the accumulation of knowledge from new instruments, and research techniques developed during World War II prepared the way for the development of the convection cell theory of crustal movement.
Midocean ridges and rises, major transform faults, and trenches should be included and conclusions drawn about their relationships.
The average displacement of the magnetic stripes from the ridge crest is
www.geo.lsa.umich.edu /classes/geo222/answers1.html   (929 words)

 Hot News From The Deep Sea - Brief Article Rocks & Minerals - Find Articles
Scientific expeditions to a particularly intriguing area of the deep-sea environment--the midocean ridge system--have led to remarkable discoveries, including vast ore deposits, fantastic ecosystems, and new details relating to plate tectonics.
The midocean ridge system is an enormous volcanic mountain chain winding through the ocean basins (fig.
Scientists are currently investigating several parts of the ridge system, including the Juan de Fuca Ridge in the northeast Pacific Ocean, the East Pacific Rise west of South America, and segments of the Mid-Atlantic Ridge in the northern Atlantic Ocean.
www.findarticles.com /p/articles/mi_m0GDX/is_3_75/ai_62214070   (410 words)

 PMEL Publications Search   (Site not responding. Last check: 2007-10-23)
Previous models and calculations of the global mass balance of Sr in the oceans have shown that the input of unradiogenic basaltic Sr from on-axis midocean ridge hydrothermal systems is much less than needed to balance the input of radiogenic Sr delivered to the oceans by rivers.
Sr ratio of pore fluids in ridge-flank hydrothermal areas is virtually indistinguishable from the seawater ratio or is dominated by authigenic carbonates.
Sr ratios of warm springs, sediment pore fluids, and basement reservoir fluid with a clear basaltic signature from the eastern flank of the Juan de Fuca ridge (JFR).
jelly.pmel.noaa.gov /admin/scripts/publications.asp?ABSTRACT_REQUEST=1962   (435 words)

 Geophysical Research Letters - Vol. 26, No. 23
The formation of ocean crust along the midocean ridge system is volumetrically one of the most important geological processes on the surface of the earth.
Volcanic eruptions along the ridge can be catastrophic events during which magma rises to the surface of the sea floor to release heat and gases into turbulent megaplumes that disrupt the overlying water column, initiate and rejuvenate hydrothermal circulation, and trigger an outpouring of microbial debris.
Instruments in place for the first time during such a midocean ridge volcanic event measured ground deformation and caldera subsidence resulting from the extraction of magma as described by Fox [3437] and Chadwick et al.
www.agu.org /pubs/toc/gl/gl/gl9923/gl_26_23.html   (2482 words)

 g07 Lynn Sykes' proof of seafdloor spreading
Midocean ridges occur as offset lengths between fault lineaments orthogonal to them.
If the ridge offsets are due to strike slip, the lineaments will have fault seismicity along their length and the fault motion will be in the sense of the offset (be it right- or left lateral).
If the ridge offsets are original, and seafloor spreads from the ridges, seismicity will be confined to portion of the fault lineament between the offset ridge segments and fault motion will be in the opposite sense to the apparent fault displacement.
geowords.com /histbooknetscape/g07.htm   (175 words)

Tivey, M.A. Schouten and M.C. Kleinrock, A near-bottom magnetic survey of the Mid-Atlantic Ridge axis at 26°N: Implications for the tectonic evolution of the TAG segment, J.
Tivey, M.A., and H. Schouten, Magnetism of the midocean ridge axis and implications for crustal accretion, EOS Trans.
Tivey, M.A. and H.P. Johnson, Crustal evolution and the implications for the magnetization of oceanic crust, EOS Trans.
deeptow.whoi.edu /pubs.html   (3852 words)

 [No title]   (Site not responding. Last check: 2007-10-23)
Located between the plate boundary at the Gakkel (Arctic Midocean) Ridge on the west and the Lomonosov Ridge on the east.
Because of being largely isolated from sediment sources on the Barents shelf by the Gakkel Ridge, the seafloor of the Amundsen basin is deeper than that of the Nansen basin, and basinal morphology is thereby better developed.
Where the Laptev continental rise sedimentary prism overlaps and obscures the Mid-Arctic Ridge, the boundary between the Amundsen and Nansen Basins is placed along the projection of the midocean ridge beneath the continental rise.
pubs.usgs.gov /of/1999/of99-422/norpac/data/terranes/nor_pac/explanat/terranes/AN.txt   (330 words)

Kleinrock and his students are studying volcanoes, faulting, hydrothermal activity, and mass wasting near "TAG", one of the largest known hydro-thermal vent systems on the midocean ridge.
He is studying the mechanisms of lithospheric deformation associated with migrating non-transform offsets, which are now known to be far more common along midocean ridges than classical transform faults.
Faulting on the median valley floor of the TAG segment, 26°10'N, Mid-Atlantic Ridge: Implications for fault growth and scaling in oceanic lithosphere.
www.vanderbilt.edu /AnS/geology/kleinrock.htm   (389 words)

 A Science Odyssey: People and Discoveries: Magnetic bands provide evidence of sea-floor spreading
In 1963, Fred Vine, Drummond Matthews, and others found that the crust surrounding the midocean ridges showed alternating bands -- each band magnetized with a polarity opposite the surrounding bands.
They suggested that as new sea-floor crust was formed around the rift in the midocean ridge, it magnetized differently, depending upon the polarity of the planet at that time.
This supported the theory that Harry Hess had put forth, that the ocean progressivley widens as new sea floor is created along a crack that follows the crest of midocean ridges.
www.pbs.org /wgbh/aso/databank/entries/do63ma.html   (222 words)

 AMNH - Spreading
On the map you may notice the smaller lines that cut across the midocean ridge like rail road tracks and cause the steplike appearance of the midocean ridge system.
Notice that the ocean basins are much deeper (purple) farther away from the midocean ridges and shallower (blue) closer to the midocean ridges.
Oceanic crust is therefore younger near the midocean ridges and increasingly older farther from the midocean ridges.
www.amnh.org /nationalcenter/expeditions/blacksmokers/spreading.html   (567 words)

 A Science Odyssey: People and Discoveries: Great Global Rift is discovered
This expedition was the first use of closely spaced echo sounders to map deep sea topography and the first to reveal the extent of the sea floor's rugged terrain.
The expedition also found that a continuous mountain-like ridge runs through the Atlantic to the southwest of Africa.
That ridge, it was later discovered, extended through the major oceans of the world.
www.pbs.org /wgbh/aso/databank/entries/do53ri.html   (399 words)

 WHOI : People : Rob L Evans : Projects
The process of new crustal formation at a midocean ridge involves a complex series of interactions between newly delivered melt from the mantle, and seawater which penetrates deep into the crust through cracks and faults, removing heat from the crust.
Magnetometers were placed on the ridge crest in areas of known hydrothermal activity, in axial sites devoid of venting, and further off-axis to a distance of approximately 4km.
The western side of the ridge appears to contain a small percentage of interconnected melt, broadly consistent with seismic results, but there is little evidence for melt more than a few kilometres to the east of the ridge (Evans et al., 1999; Baba et al., in press).
www.whoi.edu /hpb/viewPage.do?id=568&cl=1   (743 words)

 Untitled Document
They discovered that the rocks on the ocean floor produced fluctuating magnetic intensities as they crossed the ridge and that this patter appeared to be symmetrical with the axis of the ridge as the line of symmetry.
If new lithosphere was being generated at the midocean ridges, then Earth would have to be expanding unless tere was some mechanism for recycling oceanic lithosphere.
Earthquake activity is confined to the midocean ridge but the new ocean basin is so small that the quakes can usually be felt on both shores.
www2.brevard.edu /reynoljh/onlinegeology/tectonics/platetectonics3.htm   (3995 words)

 2-Subduction Sophistry
When the Atlantic Midocean Ridge was found to be creating (propagating) new ocean seafloor and increasing the distance between Europe/Africa and the Americas, scientists realized this could mean the Earth might be increasing in diameter because the Atlantic basin was obviously increasing in width.
The total new seafloor growth, both E-W and N-S, along the ~65,000 kilometers of midocean ridges undoubtedly exceeds ~300 mm/yr (~12 in/yr), and ALL of it must be vectored into the Pacific Ocean basin, the only area on the planet where subduction is believed to occur.
Midocean ridges are the enabling mechanism of global expansion, acting like cranial sutures that permit the human skull to grow to maturity
www.expanding-earth.org /page_2.htm   (3278 words)

 Columbia News ::: Evidence of Recent Volcanic Activity Found along the Slow Spreading Gakkel Ridge   (Site not responding. Last check: 2007-10-23)
A team of researchers from Columbia, the University of Hawaii at Manoa and Tulane collected data along the Gakkel Ridge, the Earth's slowest spreading MOR, which was thought to be non-volcanic.
The presence of linear magnetic abnormalities over the entire ridge also suggests the ridge is volcanic.
Three profiles across the axis of Gakkel Ridge depict a central high on the axial valley floor that may be a constructional ridge similar to those observed on the slow-spreading Mid-Atlantic Ridge.
www.columbia.edu /cu/news/01/03/gakkel.html   (795 words)

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