structure and evolution of the Earth's crust is determined not only development, but also the origin of the general topography of the ocean floor.There are two groups: the phenomenon of oceanic plateau transition structure of the crust and the median ridge with abyssal plains and trenches.
Attempts classification
To summarize the information about the structure of the ocean floor is set a single planetary system.Mid-ocean ridges are located almost in the middle of the main oceanic spaces, dividing them into equal parts.There are several attempts to classify.Menard, for example, distinguishes them so:
- wide ridges with pronounced seismicity (eg. East Pacific);
- narrow ridges with steep slopes and seismic activity (eg. Mid-Atlantic Ridge);
- narrow and steep, but not having the ridges of seismic activity (eg. Pacific Fair and Tuamotu).
By GB Udintsevu, mid-ocean ridges have no analogues on land.DG Panov considers underwater ridges in the Pacific Ocean to the corners of the platform - internal and external - and treats them as analogues of continental platforms.However, the tectonic structure of the mid-ocean ridge can not be classified as ground tectonics.Too high amplitude tectonic shifts and grandly over a relatively continental - ground structures.
Formation
One of the most common forms of rock formations in the oceans - ocean shafts.Most of all, they represent the Pacific Ocean.There are two varieties:
- type anticlinal uplifts with the most ancient rocks in the core;
- ocean with trees occurring volcanic cones, including extinct volcanoes (Guyot).
time education
ridge of the Middle Age is determined by the structure of the crust - it is continental or oceanic.You can see many areas in connection with the Alpine structures, strongly fractured and deeply lowered into the ocean.For example, the area adjacent to the sea from Fiji.
mid-ocean ridges anticlinal - gentle slopes, the individual and rather rare underwater volcanoes - almost dissected.This is a newly formed, and the most basic kinds of deformation of the ocean floor in the form of platform fragmentation and intense seismic and volcanic activity.As you know, it all started during the Cenozoic Quaternary.Anticlinal formation - mid-ocean ridges - are formed and grow and now.
second type of rock formations in the oceans - ocean trees - are more in height and length.The elongated linear lifting with gentle slopes are much thinner crust.This structure has many mid-ocean ridges.Examples: South Pacific, East Pacific and others.
It is more ancient formation, volcanoes were formed for them in the Tertiary period, and later formation of seamounts continued.The break-up of deep faults was repeated several times.
structure of the mid-ocean ridge
ocean ridges in the areas of fragmentation - is the most difficult terrain.The sharpest division structure is found in places where forming mid-oceanic ridges, such as the Atlantic and Indian oceans, the South Pacific, Southern Ocean from Africa, the area between Australia and Antarctica.
One of the most characteristic features of this type of structure - grabens (deep valleys), flanking a series of high (up to three kilometers) vertices, alternating abruptly towering volcanic cones.A bit like the Alpine character of the structure, but the contrast is greater division of more pronounced than in the structure of the continental mountain belts.
In the absence of a secondary (and fractional) dissection, which has a middle ridge and all its slopes, we can talk about the signs of the recent formation of relief.Then, in the bottom of the slope there are terrace-smooth surface with ledges, separated from each other.This former step faults.Notably - Rift Valley, which divides in half the median ridge.
How extends the planetary ocean rift zones is determined by the crushing.This is the most pronounced form of manifestation of tectonics on the last leg of a large geological time.Tectonic structure of mid-ocean ridge can be different.For example, Kamchatka - area of active tectonic processes, volcanism is modern and there is constant.Lithospheric plates Okhotsk block processed oceanic crust, forming the mainland, and the median ridge of Kamchatka - the object of continuous monitoring of the process.
Location
Lithospheric plates are in motion and pushing the (so-called divirgentsii) of ocean crust is transformed.The bed of the oceans rises, forming a 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.You can start with the Gakkel Ridge in the Arctic Ocean - from the Laptev Sea to Spitsbergen.Then continue without interruption his line to the south.There's Mid-Atlantic Ridge stretches to the island of Bouvet.
Next Pointer leads and west - this American-Antarctic Ridge, and to the east - on the African-Antarctic, continuing Southwest Indian Ocean.Here again the triple junction - the Arabian-Indian Ridge should be the meridian, and Southeast Indian Ocean extending to the Australasian Antarctic.
This is not the end of the line.Continuation of the South Pacific Rise, rolling in the East Pacific Rise, which goes north to California, in the San Andreas Fault.This is followed by a middle ridge Strait of Juan de Fuca - to Canada.
belted a planet more than once, the lines laid pointer, clearly indicate where the form of the mid-ocean ridges.They are everywhere.
Relief
Mid-ocean ridges are formed on Earth as a giant necklace and a half thousand kilometers in width, the height of the basins is above three, four kilometers.Sometimes vreshiny protrude from the ocean depths, forming islands, mostly volcanic.
Even the ridge reaches a width of one hundred kilometers.Of particular beauty give harsh ruggedness of terrain and the very small-block structure.Along the axis of the ridge is usually held Rift Valley thirty kilometers in width with the axial rift (four five-kilometer-wide slit height of many hundreds of meters).
At the bottom of the rift present young volcanoes, surrounded hydrotherms - hot springs that produce metal sulphides (silver, lead, cadmium, iron, copper, zinc).There are constant small earthquakes.
Under axial rifts magma chambers are connected kilometer, that is sufficiently narrow channel with the central eruptions at the bottom of the slot.Side of the range is much wider crest - hundreds and hundreds of kilometers.They are covered with layers of lava sediments.
Not all parts of the system are the same: some mid-ocean ridges wider and flatter, instead of Rift Valley have a projection of oceanic crust.For example, the East Pacific Rise and the South Pacific and others.
Each median ridge dissected along transform (ie, lateral) faults in many places.For these faults, the ridge axis shifted by the distance of hundreds of kilometers.Land intersection blurred in the chute, that is hollow, some of which dostinayut to eight kilometers deep.
longest underwater mountain chain
longest mid-ocean ridge is located on the bottom of the Atlantic Ocean.He shares the North American and Eurasian tectonic plates.Lasts Mid-Atlantic Ridge 18 000 kilometers.It is part of the oceanic ridges to forty thousand kilometers.
consists median ridge of the Atlantic by a number slightly smaller: Knipovich and Mona ridges, Iceland-Yanmayetsky and Reykjanes, as well as very large - the length of more than eight thousand kilometers of the North Atlantic Ridge and ten and a half thousand kilometers - the South Atlantic.
Here the mountains are so high that formed a chain of islands: this Azores and Bermuda, and even Iceland, Saint Helena, Ascension Island, Bouvet Island, Gough, Tristan da Cunha, and many smaller ones.
geological calculations say that middle ridge formed in the Triassic period.Transverse faults shift the axis up to six kilometers.The top of the ridge complex consists of tholeiitic basalts, and the bottom - it amphibolites and ophiolites.
Global System
most prominent structure in the ocean - stretch for sixty thousand kilometers of mid-ocean ridges.They were divided into two almost equal halves Atlantic and Indian - in three parts.In the Pacific middleness slightly pumped up: necklace ridges moved down to the side, to South America and then to the isthmus between the continents to go under the mainland of North America.
Even in a small Arctic Ocean has Gakkel Ridge, which is clearly seen tectonic structure of mid-ocean ridge, which is equivalent to raising the mid-ocean.
Huge swelling of the ocean floor - a plate boundaries.The Earth's surface is covered with plates of these plates, which are not lezhitsya in place: they are constantly crawl on each other, breaking the edges, releasing magma increasing and with its help the new body.For example, North American Plate covered with its edge of two neighbors, forming ridges Strait of Juan de Fuca and Gorda.Expanding, lithospheric plate is usually absorbed and infringes territory slabs lying around.The continents also suffer from this more than anything.They are in this game look like hummocks: under the mainland goes oceanic crust, lifting him, crushing and breaking.
rift zone
under the center of each section of the ridges rising magma flows, stretching the Earth's crust by breaking its edge.Outflow at the bottom, the magma cools, increasing the mass range.Then a new piece of mantle melt breaks and crushes new foundation, and everything is repeated.Because the ocean is increasing the earth's crust.This process is called spreading.
spreading rate (the formation of the ocean floor) detects changes appearance ranges from one section to another.And it is with the same structure.Where speeds are different, the ridge in the landscape changes completely, too.
Where the spreading rate is low (eg. Rift Tajura) formed huge underwater valleys with active volcanoes on the bottom.They dive below the ridge for about four hundred meters, where there is a gradual raising of terraced steps on a hundred - a hundred and fifty meters each.This rift is in the Red Sea, and in many areas of the Mid-Atlantic Ridge.These oceanic mountains grow slowly, several centimeters per year.
At high speed spreading ridges (especially in cross-section) are as follows: central lifting half a kilometer above the ground relief and executed chain of volcanoes.Such, for example, the East Pacific Rise.There Valley does not have time to form, and the rate of increase of the crust in the ocean can be very high - 18-20 cm a year.Thus it is possible to determine the age and the median ridge.
unique phenomenon - the "black smokers"
tectonic structures of the median ridge allowed to appear such an interesting natural phenomenon as "black smokers".Hot lava ocean water warms up to three hundred and fifty degrees.The water came forth to the ferry, if there were such incredible pressure of the ocean many kilometers thick.
Lava carries a variety of chemicals that are dissolved in water, the interaction of form sulfuric acid.Sulfuric acid, in turn, dissolves many minerals streamed lava, interacts with them and forming metals and sulfur compounds (sulfides).
precipitate of them drops a cone height of about seventy meters, within which all the above reactions continue.Top cone rises fiery sulfide solution and break the will of the black clouds.
very spectacular.However, the approach is dangerous.The most interesting is that the hidden and most active part of each cone is many hundreds of meters high.And far above the Ostankino tower for example.When the cones are many, it seems that there is work underground (and underwater) secret plant.Most often they occur in droves.
Central Range of Kamchatka Peninsula
landscape unique.The mountain range, which is Dividing Range on the Kamchatka Peninsula - Central Range.Its length is 1,200 km, runs from north to south, and bears a huge number of volcanoes - most of the thyroid and stratovolcanoes.Is there a plateau of lava, and some mountains and isolated peaks covered with eternal glaciers.Bystrinsky stand out most clearly, and Malkinskiy Kozyrevsky ranges.
highest point - 3621 m - Ichinsky.Almost level with it many volcanoes: Alna, Khuvkhoitun, Shishelov, Acute Sopka.The range consists of twenty-eight of eleven passes and peaks, most of which are in the northern sector.The central part is characterized by significant distances between the peaks in the southern part - high ruggedness on asymmetric arrays.
tectonic structures of the Middle Range of Kamchatka was formed during long-term cooperation of the largest lithospheric plates - the Pacific, Kula, the North American and Eurasian.
