Tectonic plates

Tectonic plates

Tectonic plates can move in relation to each other.

Geography

Keywords

tectonic plate, plate tectonics, lithosphere, crust, mantle, core, asthenosphere, volcanic activity, magma, fault line, oceanic ridge, oceanic trench, fold mountain, earthquake, ocean, nature, geography

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The solid, outermost shell of the Earth is called the lithosphere. This includes the crust and the upper, solid part of the mantle. On average, it is 50 km (31 mi) thick beneath the oceans and 70–100 km (43.5–62.1 mi) thick under the continents. The continental lithosphere and the oceanic lithosphere also differ in composition. The continental crust floats on the asthenosphere, the viscous upper part of the mantle that lies beneath the lithosphere.

The movement of the lithosphere, which can be observed in a great number of places, is the reason behind earthquakes and volcanic activity. These movements do not take place randomly, but along longitudinal belts. Volcanic activity and earthquakes mostly occur at the edge of continents, in oceanic island arcs, oceanic trenches, and mid-ocean ridges. These motion processes mark the boundaries of tectonic plates.

The lithosphere is not uniform, it is broken up into tectonic plates of different sizes. Today, we know of seven major tectonic plates and a number of other, smaller ones, which all move in relation to each other. The seven major tectonic plates are: the African plate, the Eurasian plate, the North American plate, the South American plate, the Pacific plate, the Indo-Australian plate and the Antarctic plate.

The theory that describes the motion of the lithosphere is called plate tectonics. There are three types of tectonic movement: convergence, divergence and subduction.

Mid-ocean ridges represent an example of divergent plate boundaries. As magma, that is, molten rock, rises from the asthenosphere and penetrates the oceanic lithosphere, it reaches the surface, where it cools down and solidifies, forming new lithosphere at the edge of the crack. That is how mid-ocean ridges are formed. As it expands, the mass of molten rock pulls the sea floor apart, causing the tectonic plates on either side of the ridge to move away from each other. Thus the ocean basin grows wider, a process called sea floor spreading. That is how, for example the Atlantic Ocean has been formed.

However, since the surface of the Earth cannot increase continuously, the surface of oceans cannot increase continuously either. The opposite boundary of the oceanic plates approaches another plate. When the two tectonic plates collide, one plate moves beneath another. This is called subduction. The subducting plate moves into the asthenosphere where it is melted and incorporated into the mantle.

At subduction zones, volcanoes, fold mountains and deep sea trenches occur. Examples of mountain ranges formed as a result of subduction are the Andes and the Himalayas.

On rare occasion, it may happen that two adjacent plates slip along a fault, resulting in an earthquake. This is the case with the San Andreas Fault in California.

Oceanic lithosphere is formed continuously at mid-ocean ridges and disappears at oceanic trenches. Thus, the size of continental plates and the location of dry land are continuously changing.

  • - The oceanic crust is thinner (5–15 km or 3.1-9.3 mi) and consists of rock rich in silicates and magnesium; its density is 3.2 g/cm³ (0.1156 lb/in³). Continental crust is thicker (30-65 km or 18.6–40.4 mi) and consists of rock rich in silicates and aluminum; its density is 2.7–3 g/cm³ (0.09754–0.1084lb/in³).
  • - It extends to a depth of 700 km (435 mi); its density is 3.3–4 g/cm³ (0.1192–0.1445 lb/in³).
  • - A solid layer, extending to a depth of 2,900 km (1,802 mi). Its density is 4–5.5 g/cm³ (0.1445–0.1987 lb/in³) .
  • - A viscous layer, extending to a depth of 5,150 km (3,200 mi). Its density is 10.5–12.3 g/cm³ (0.3793–0.4444 lb/in³).
  • - A solid layer, extending to a depth of 6,371 km (3,959 mi). Its density is 13.3 g/cm³ (0.4805 lb/in³).
  • - The rigid, outermost shell of the Earth. It includes the crust and the topmost, solid layer of the upper mantle. It is about 50–100 km (31–62.1 mi) thick and its density is 3.3 g/cm³ (0.1192 lb/in³).
  • - A molten layer of the upper mantle; about 550–600 km (341.8-372.8 mi) thick. Its density is 3.4–4 g/cm³ (0.1228-0.1445 lb/in³). Tectonic plates float on this layer.

  • - A molten layer of the upper mantle; about 550–600 km (341.8–372.8 mi) thick. Its density is 3.4–4 g/cm³ (0.1228–0.1445 lb/in³). Tectonic plates float on this layer.

Narration

The solid, outermost shell of the Earth is called the lithosphere. This includes the crust and the upper, solid part of the mantle. On average, it is 50 km (31 mi) thick beneath the oceans and 70–100 km (43.5–62.1 mi) thick under the continents. The continental lithosphere and the oceanic lithosphere also differ in composition. The continental crust floats on the asthenosphere, the viscous upper part of the mantle that lies beneath the lithosphere.

The movement of the lithosphere, which can be observed in a great number of places, is the reason behind earthquakes and volcanic activity. These movements do not take place randomly, but along longitudinal belts. Volcanic activity and earthquakes mostly occur at the edge of continents, in oceanic island arcs, oceanic trenches, and mid-ocean ridges. These motion processes mark the boundaries of tectonic plates.

The lithosphere is not uniform, it is broken up into tectonic plates of different sizes. Today, we know of seven major tectonic plates and a number of other, smaller ones, which all move in relation to each other. The seven major tectonic plates are: the African plate, the Eurasian plate, the North American plate, the South American plate, the Pacific plate, the Indo-Australian plate and the Antarctic plate.

The theory that describes the motion of the lithosphere is called plate tectonics. There are three types of tectonic movement: convergence, divergence and subduction.

Mid-ocean ridges represent an example of divergent plate boundaries. As magma, that is, molten rock, rises from the asthenosphere and penetrates the oceanic lithosphere, it reaches the surface, where it cools down and solidifies, forming new lithosphere at the edge of the crack. That is how mid-ocean ridges are formed. As it expands, the mass of molten rock pulls the sea floor apart, causing the tectonic plates on either side of the ridge to move away from each other. Thus the ocean basin grows wider, a process called sea floor spreading. That is how, for example the Atlantic Ocean has been formed.

However, since the surface of the Earth cannot increase continuously, the surface of oceans cannot increase continuously either. The opposite boundary of the oceanic plates approaches another plate. When the two tectonic plates collide, one plate moves beneath another. This is called subduction. The subducting plate moves into the asthenosphere where it is melted and incorporated into the mantle.

At subduction zones, volcanoes, fold mountains and deep sea trenches occur. Examples of mountain ranges formed as a result of subduction are the Andes and the Himalayas.

On rare occasion, it may happen that two adjacent plates slip along a fault, resulting in an earthquake. This is the case with the San Andreas Fault in California.

Oceanic lithosphere is formed continuously at mid-ocean ridges and disappears at oceanic trenches. Thus, the size of continental plates and the location of dry land are continuously changing.

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