Mid-Ocean Ridges


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Related to Mid-Ocean Ridges: sea-floor spreading

Mid-Ocean Ridges

 

major relief features on the floor of the world ocean, forming a single system of mountain structures more than 60,000 km long. The ridges have relative altitudes of 2,000–3,000 m and a width of 250–450 km, although in some places the width reaches 1,000 km. Morphologically, the ridges represent linear uplifts of the earth’s crust with very rugged crests and slopes. Whereas in the Pacific and Arctic oceans the ridge is located in the marginal parts of the ocean, in the Atlantic it passes through the middle.

Rifts, which form as a result of the pulling apart of the earth’s crust, occur in the axial zone of the mid-ocean ridges. In addition to faults oriented along the mid-ocean ridges, there are also transverse faults, which often extend into neighboring parts of the ocean bed. The basalts that make up the earth’s oceanic crust and such ultrabasic rocks as harzburgites, dunites, and serpentin-ites are exposed in the rifts and transverse fault zones. Substantial seismicity and an increase in the heat flow from the earth’s interior are associated with the faults; volcanic activity also occurs in places. With respect to the composition of the products of eruption, the volcanoes of the mid-ocean ridges and those of the ocean floor are similar and differ sharply from the volcanoes of the transitional zones (modern geosynclinal regions) in that there is an absence of acidic and andesitic lavas and tuffs.

The volcanic islands located in the axial zone of the mid-ocean ridges, and sometimes on their slopes, are the peaks of the largest underwater volcanoes. Most of the volcanoes are inactive, although there are active volcanoes in the Azores, in the Tristan da Cunha Islands, and elsewhere. The largest underwater volcanoes, as well as the epicenters of earthquakes, are associated with the places where the transverse faults cross the axial zone.

The transverse faults divide the mid-ocean ridges into segments that are usually displaced horizontally by up to 500–600 km relative to one another. In the new global tectonics great importance is ascribed to these horizontal movements. The mid-ocean ridges are considered to be zones where oceanic crust is being formed from material rising to the rift zones out of the mantle and spreading laterally. According to other theories, the mid-ocean ridges are folded structures, and their Neogene-Anthropo-gene phase of development is a counterpart to the orogenic phase of the continental folded systems, marked by uplifts and a pulling apart of the earth’s crust (A. V. Peive, 1975). Some scientists believe that the formation of the mid-ocean ridges is associated with the pulling apart and bulging of the crust, caused by the flow of abyssal material from the mantle, and with the accompanying phenomena of serpentinization.

REFERENCES

Leont’ev, O. K. Dno okeana. Moscow, 1968.
Udinstev, G. B. Geomorfologiia i tektonika dna Tikhogo okeana. Moscow, 1972. (Tikhii okean, vol. 5.)
Issledovaniia po problème riftovykh zon Mirovogo okeana, vols. 1–3. Moscow, 1972–74.
Peive, A. V. “Tektonika Sredinno-Atlanticheskogo khrebta.” Glubinnoe stroenie i geofizicheskie osobennosti struktur zemnoi kory i verkhnei mantii. Moscow, 1975.
The Sea, vols. 3–4. New York-London, 1963–70.
Heezen, B. C, and C. D. Hollister. The Face of the Deep. London, 1971.

O. K. LEONTEV

References in periodicals archive ?
At mid-ocean ridges, the tectonic plates that form the seafloor gradually spread apart," said Sarafian.
Unlike most other mid-ocean ridges, the East Pacific Rise as a whole has not moved east-west for 50,000,000 to 80,000,000 years, even as parts of it have been spreading asymmetrically.
These topographic alignments are approximately parallel to the ridge segments and to the pseudofaults, showing that their origin took place at the axis of the mid-ocean ridge (Fig.
2008), the accumulated data demonstrate the high degree of geochemical heterogeneity, and the small scale of this heterogeneity, in mid-ocean ridges and seamounts off Canada's west coast.
Careful study of the 2005 mega-dike intrusion and its aftermath will continue to provide extraordinary opportunities for learning about continental rifts and mid-ocean ridges.
The range, located in the moon's southern hemisphere, may have formed in a manner similar to mid-ocean ridges on Earth: tectonic forces pulled Titan's crust apart, allowing ice to well up from the interior.
The code of conduct has been put together by InterRidge, a science-based non-profit organisation that represents the research-based groups that are exploring the geology of the mid-ocean ridges, 2 kilometres under the surface of the oceans.
Magma erupting at the mid-ocean ridges drives a hydrothermal circulation system--much like deep-sea "Old Faithful" geysers, except that they are under enormous pressure, with temperatures as high as 350[degrees]C.
Scientists to Use Deep-Diving REMUS to Study Volcanic and Tectonic Processes at Mid-Ocean Ridges to Understand Their Influence on Hydrothermalism
The researchers say falling sea levels released the amount of pressure on the Earth's upper mantle - which is below the crust - and "may have induced a surge in magma" coming from both ocean volcanoes and mid-ocean ridges, which are underwater mountains formed through the plate tectonics of the planet, with topography changing where plates meet and collide.
Glacial cycles redistribute water between the oceans and continents, changing sea level and hence varying the load on mid-ocean ridges.