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 ?
But Sentry had already been committed to another expedition in March, so ABE was brought back into service for a mission to explore the Chile Triple Junction, the only place on Earth where a mid-ocean ridge is being subducted (or pushed beneath) a continent (South America) in a deep ocean trench.
In 2006, the WHOI autonomous underwater vehicle ABE collected hundreds of images from around an unexplored region of the mid-ocean ridge with the hopes of using the physical appearance of the seafloor, rather than its bathymetry (or depth), to create a new way to study how lava flows create features on the seafloor.
We are honored to have an opportunity to lead the international community in promoting and coordinating scientific research and exploration of the fascinating deep-ocean geological, hydrothermal, and biological processes along the global mid-ocean ridges." (For more information, visit interridge.whoi.edu.)
Called transform faults, they connect adjacent segments of the spreading center and give Earth's mid-ocean ridges a characteristic staircase-like appearance.
He covered tsunamis; the effects of sea level rise and other processes on shoreline erosion; and seafloor features from mid-ocean ridges and seamounts and their distinctive biological communities to deep-sea vents and their unique interplay of geologic, chemical, and biological processes.
They would also like to see if they can link chemistry and depth on much smaller scales--along individual segments of mid-ocean ridges, for example.
Lavas erupted at mid-ocean ridges and at oceanic islands have different compositions of trace elements and noble gases.
Scientists have long known that lavas coming from mid-ocean ridges where new seafloor is created become magnetized as the cool in the presence of the earth's magnetic field; the series of stripes with different magnetic orientations forms because the earth's field reverses direction from time to time.
And we have compared those with rocks from active mid-ocean ridges on the seafloor.
Like all mid-ocean ridges, the Gakkel Ridge is an undersea volcanic mountain chain where magma erupts to create new ocean crust that spreads out on both sides of the ridge.
By dating rock recovered from numerous seafloor locations, researchers in the early 1970s confirmed the basic cycle of plate tectonics: New ocean crust forms at mid-ocean ridges and spreads outward toward deep-sea trench subduction zones.