The structure and development of the earth's crust determines not only the development, but also the origin of the general relief of the ocean floor. Two groups are distinguished here: the oceanic plateau as a phenomenon of the transitional type of the structure of the earth's crust and the median ridge with abyssal plains and trenches.
Classification attempts
To summarize information about the structure of the ocean floor, a single planetary system has been established. Mid-ocean ridges are located almost in the middle of the main ocean spaces, dividing them into equal parts. There are several attempts at classification. Menard, for example, distinguishes them in this way:
- wide underwater ridges with pronounced seismicity (eg East Pacific);
- narrow submarine ridges with steep slopes and seismic activity (ex. Mid-Atlantic Ridge);
- narrow and steep, but not seismically active underwater ridges (eg Mid-Pacific and Tuamotu).
According to GB Udintsev, mid-ocean ridges have no analogues on land. D. G. Panov refers the submarine ridges in the Pacific Ocean to the corners of the platform - internal and external - and considers them as analogues of the continental platforms. However, the tectonic structure of the Mid-Range cannot be classified as terrestrial tectonics. The amplitude of tectonic shifts is too great and the extension is grandiose relative to continental - terrestrial structures.
Formation
One of the most common forms of rock formations in the oceans is oceanic swells. Most of all they are represented by the Pacific Ocean. There are two varieties:
- anticlinal type of uplifts with the oldest rocks in the core;
- ocean swells with occurring volcanic cones, including extinct volcanoes (guyotes).
Education time
The age of the Sredinny Ridge is determined by the structure of the crust - is it continental or oceanic. Many areas can be considered in connection with alpine structures, highly fragmented and deeply lowered into the ocean. For example, the area adjacent to the sea off Fiji.
Mid-oceanic ridges of anticline type - gentle slopes, separate and rather rare underwater volcanoes - are almost not dissected. These are the most recently formed and simplest types of deformation of the ocean floor in the form of platform fragmentation and intense seismicity and volcanism. As you know, all this began during the Cenozoic-Quaternary. Anticlinal formations - mid-oceanridges - are being formed and are growing at the present time.
The second type of rock formations in the oceans - oceanic shafts - are characterized by greater height and length. Elongated linear uplifts with gentle slopes have a much thinner crust. Many mid-ocean ridges have this structure. Examples: South Pacific, Eastern Pacific, and more.
These are more ancient formations, volcanoes formed on them in the Tertiary time, and the formation of seamounts continued later. The fragmentation of deep faults was repeated many times.
Structure of the median ridge
Ocean ridges in crushing zones are the most difficult relief. The sharpest division of the structure is found in those places where the Mid-Ocean Ridges are formed, such as the Atlantic and Indian Oceans, the South Pacific, the Southern Ocean from Africa, the zone between Australia and Antarctica.
One of the most characteristic features of this type of structure is the grabens (deep valleys) bordering a series of high (up to three kilometers) peaks, interspersed with sharply rising volcanic cones. A bit like the alpine character of the structure, but there are more contrasts, the division is more pronounced than in the continental structure of the mountain belts.
In the absence of secondary (and more fractional) dissection, which has a median ridge and all its slopes, we can talk about signs of a recent relief formation. Then in the lower part of the slope there are even terrace-like surfaces with ledges separated from each other.friend. These are former step faults. Notable is the rift valley that bisects the median ridge.
How far the planetary oceanic fault extends is determined by the size of the crushing zones. This is the most pronounced form of manifestation of tectonics in the last segments of the great geological time. The tectonic structure of the median ridge can be different. For example, Kamchatka is an area of active tectonic processes, volcanism there is modern and constant. The lithospheric plates of the Okhotsk block process the oceanic crust, forming the continental one, and the middle ridge of Kamchatka is the object of constant monitoring of this process.
Location
The lithospheric plates are in motion, and when moving apart (the so-called divergence), their oceanic crust is transformed. The bed of the oceans rises, forming mid-ocean ridges. They were classified in the fifties of the twentieth century in the world system with the active participation of the Soviet Union.
Mid-ocean ridges have a total length of more than sixty thousand kilometers. Here you can start from the Gakkel Ridge in the Arctic Ocean - from the Laptev Sea to Svalbard. Then continue without breaking his line to the south. There, the Mid-Atlantic Ridge stretches to Bouvet Island.
Further, the pointer leads both to the west - this is the American-Antarctic ridge, and to the east - along the African-Antarctic, continuing the Southwestern Indian Ocean. Here again the triple junction - the Arabian-Indian ridgefollows the meridian, and the Southeast Indian Ocean stretches to the Australo-Antarctic one.
This is not the end of the line. Continuation along the South Pacific Rise, turning into the East Pacific Rise, which goes north to California, into the San Andreas Fault. Next comes the middle ridge of Juan de Fuca - to Canada.
Having encircled the planet more than once, the lines drawn by the pointer clearly show where mid-ocean ridges form. They are everywhere.
Relief
Mid-ocean ridges are formed on the globe like a giant necklace up to one and a half thousand kilometers wide, while their height above the basins can be three or four kilometers. Sometimes crevices protrude from the depths of the ocean, forming islands, most often volcanic.
Even the crest of the ridge itself reaches a width of one hundred kilometers. The sharp dissection of the relief and the small-block structure itself give special beauty. Along the axis of the ridge, there usually runs a rift valley about thirty kilometers wide with an axial rift (a four-five-kilometer wide gap many hundreds of meters high).
At the bottom of the rift there are young volcanoes surrounded by hydrotherms - hot springs that emit metal sulfides (silver, lead, cadmium, iron, copper, zinc). Small earthquakes are constant here.
Under the axial rifts there are magma chambers connected by a kilometer-long, that is, rather narrow, channel with central eruptions at the bottom of this gap. The sides of the ridges are much wider than the ridge - hundreds and hundreds of kilometers. They are covered with layers of lava deposits.
Not all links insystems are the same: some mid-ocean ridges are wider and more gentle, instead of a rift valley they have a ledge of oceanic crust. For example, the East Pacific Rise, as well as the South Pacific and some others.
Each median ridge is dissected by transform (that is, transverse) faults in many places. Along these faults, the axes of the ridges are displaced over a distance of hundreds of kilometers. Crossings are eroded into troughs, i.e. depressions, some of which are up to eight kilometers deep.
The longest underwater mountain range
The longest mid-ocean ridge is located at the bottom of the Atlantic Ocean. It separates the North American and Eurasian tectonic plates. The Mid-Atlantic Ridge is 18,000 kilometers long. It is part of a forty thousand kilometer ocean ridge system.
The median ridge under the Atlantic consists of a number of slightly smaller ones: the Knipovich and Mona ridges, the Icelandic-Yanmayetsky and Reykjanes, as well as very large ones - more than eight thousand kilometers long, the North Atlantic Ridge and ten and a half thousand kilometers - the South Atlantic Atlantic.
Here the mountains are so high that they formed chains of islands: these are the Azores, and Bermuda, and even Iceland, St. Helena, Ascension Island, Bouvet, Gough, Tristan da Cunha and many smaller ones.
Geological calculations say that this median ridge was formed in the Triassic period. Transverse faults shift the axis up to six hundred kilometers. The upper complex of the ridge consists of tholeiiticbas alts, and the lower one is amphibolites and ophiolites.
Global System
The most prominent structure in the ocean is the 60,000-kilometer-long Mid-Ocean Ridges. They divided the Atlantic Ocean into two almost equal halves, and the Indian Ocean into three parts. In the Pacific, the middleness slightly let us down: the necklace of ridges moved to the side, to South America, then to the isthmus between the continents in order to go under the mainland of North America.
Even in the small Arctic Ocean there is the Gakkel Ridge, where the tectonic structure of the mid-ridge is clearly visible, which is equivalent to mid-ocean uplift.
Great swellings of the ocean floor are the boundaries of lithospheric plates. The surface of the Earth is covered with plates of these plates, which do not lie in place: they constantly crawl on top of each other, breaking the edges, releasing magma and building up a new body with its help. So, the North American Plate covered two neighbors at once with its edge, forming the ridges of Juan de Fuca and Gorda. Expanding, the lithospheric plate usually infringes and absorbs the territories of plates lying nearby. The continents suffer the most from this. In this game, they look like hummocks: the oceanic crust goes under the mainland, lifting it, crushing and breaking it.
Rift zones
Under the center of each section of the ridges, magma flows rise, stretching the earth's crust, breaking its edges. Pouring out to the bottom, the magma cools down, increasing the mass of the ridge. Thena new portion of the mantle melt breaks and crushes the new base, and everything repeats. This is how the earth's crust grows in the ocean. This process is called spreading.
The rate of spreading (formation of the ocean floor) determines changes in the appearance of the ridges from one area to another. And this is with the same structure. Where the speeds differ, the ridge in relief also changes completely.
Where the spreading rate is low (eg the Tajoura Rift), huge underwater valleys form with active volcanoes at the bottom. Their immersion below the ridge is about four hundred meters, from where there is a gradual terrace-like rise of steps of one hundred - one hundred and fifty meters each. There is such a rift in the Red Sea and in many parts of the Mid-Atlantic Ridge. These oceanic mountains grow slowly, a few centimeters a year.
When the spreading speed is high, the ridges (especially in cross section) look like this: the central rise is half a kilometer higher than the main relief and is shaped by a chain of volcanoes. Such, for example, is the East Pacific Rise. Here the valley does not have time to form, and the rate of growth of the earth's crust in the ocean is very high - 18-20 centimeters per year. In this way, the age of the median ridge can also be determined.
A unique phenomenon - "black smokers"
The tectonic structure of the mid-ridge allowed such an interesting natural phenomenon as "black smokers" to appear. Hot lava heats the water of the ocean to three hundred and fifty degrees. The water would have come out in steam if there had not been such an incredible pressure of the ocean duringmany kilometers thick.
Lava carries a variety of chemicals that, when dissolved in water, form sulfuric acid when interacting. Sulfuric acid, in turn, dissolves and reacts with many minerals in the erupted lava to form sulfur and metal compounds (sulfides).
The sediment falls out of them in a cone about seventy meters high, inside which all the above reactions continue. Hot solutions of sulphides rise up the cone and break free in black clouds.
Very spectacular sight. True, it is dangerous to approach. The most interesting thing is that the hidden and most actively working part of each cone is many hundreds of meters high. And much higher than the Ostankino tower for example. When there are a lot of cones, it seems that an underground (and underwater) secret factory is working there. Most often they are found in whole groups.
The middle ridge of Kamchatka
The landscape of the peninsula is unique. The mountain range, which is a watershed range on the Kamchatka Peninsula - the Sredinny Ridge. Its length is 1200 kilometers, runs from north to south and bears a huge number of volcanoes - most often shield-shaped and stratovolcanoes. There are also lava plateaus, and individual mountain ranges, as well as isolated peaks covered with eternal glaciers. The Bystrinsky, Kozyrevsky and Malkinsky ridges stand out most clearly.
The highest point - 3621 meters - Ichinskaya Sopka. Almost on a par with it are many volcanoes: Alnai, Khuvkhoytun, Shishel, Ostraya Sopka. The ridge consists of twenty-eight passes and eleven peaks, a largesome of which are in the northern section. The central part is distinguished by significant distances between the peaks, in the southern part there is a high dissection into asymmetric arrays.
The tectonic structure of the Sredinny Ridge of Kamchatka was formed during the long-term interaction of the largest lithospheric plates - Pacific, Kula, North American and Eurasian.
