Concept and Definition of Tectonic plate

What is a tectonic plate?  

tectonic plate

The term "plate tectonics" refers to structures in which our planet is made of. In geological terms, a plate is a rigid plate of solid rock that forms the surface of the Earth (lithosphere), floating above the igneous and molten rock that forms the center of the planet (asthenosphere). The lithosphere has a thickness that varies between 15 and 200 km away, being thicker in the continents than on the seabed.

Why this plate fleet, if it is so heavy?

Because compared with metals that make up the nucleus is relatively lighter (is comprised of mainly quartz and silicates).
The Earth, 225 million years ago (remember that Earth was born 4,600 million years ago), was formed on its surface by a single structure called "Pangea" (all the lands, in Greek), which was fragmented to form the continents as we know them today. Although this theory was proposed already in 1596 by the Dutch cartographer Abraham Ortelius and endorsed by the German meteorologist Alfred Lothar Wegener in 1912 to notice the similarity of forms of South America and Africa, it was only in the last 30 years, thanks to the development of science, has acquired the bearing capacity sufficient to revolutionize the understanding of many geological phenomena, among them earthquakes.
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The land before and after separating the continents.

What are the findings that confirmed the theory of Wegener?

Mainly 4:
1. The greater knowledge of the seabed thanks to the Doppler sonar, computing, etc. Determined that the bottom of the Atlantic was much thinner than previously thought, that there was an underwater mountain chain of more than 50,000 km in length covering all the Earth (Cordillera mid-Atlantic), etc.
2. The discovery of "Magnetic list" from the seafloor, which corresponds to magnetic mineral (magnetite) formed when it cools the magma from the Earth's core and arranged in stripes of reverse polarity between the two.
3 Dispersion and recycling of the crust marina. Result of explorations in search of oil, we have obtained samples of the seabed that show areas of different geological age: there are ridges or reefs are younger and trenches or deep canyons that are older. This provision is consistent with the mountain chain and this alternating magnetic polarity of the previous points. According to scientists, Harry H. Hess and Robert S. Dietz, the lithosphere of the Atlantic is expanding and the Pacific shrink. The ancient areas are anchored in the "trenches" and appear young zones on reefs, thus producing a "recycling of the seabed.
4. Greater occurrence of earthquakes in areas of ridges and trenches.

The phenomenon we could summarize by saying that these plates are in contact with each other, as huge icebergs that come together or separate, causing geological changes (and earthquakes) on the borders of the plates.
The explanation of why move is still unclear, but it could be explained by the phenomenon of convection, which refers to the influence of the temperature in the magma from the Earth's core about different minerals, with float to the hottest and sinking the most cold, similarly to as boil water in a pot. The heat would come the radioactive sifting of isotopes such as uranium, thorium, and potassium (a phenomenon which releases energy) as well as residual heat present ain since the formation of the Earth.
There are four fundamental types of frontiers or vicinity of the plates (in English: boundaries):
tectonic plate

Divergent boundaries: Where it generates new crust that fills the gap of the plates away.
The best known case of divergent border is the mid-Atlantic Ridge which made reference in the previous point and that stretches from the Arctic Ocean to southern Africa. On this border the North American and Eurasian plates at a rate of 2.5 cm are separating each year.


tectonic plate

Convergent boundaries: where the crust is destroyed at sinking one plate under another (subduction).
The best-known example is the plate of Nazca (Nazca), that it is sinking under the South American plate off the coast of Peru and Chile, giving rise to one of the most seismic areas of the planet.
The plates can converge on the continent and give rise to mountain ranges such as the as the Himalayas.
Also they can converge in the oceans, as front of the Mariana Islands, near the Philippines, giving rise to fosas marine who can reach the 11,000 m depth or lead to submarine volcanoes.

tectonic plate

Borders of transformation: where the crust is destroyed or is produced and plates only glide horizontally together.
An example of this type of border is the well-known San Andreas fault in California.


Border areas of plates: it is a wide belt that borders are not well defined and the effect of the interaction of the plates is not clear.

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    Cross section of the Earth's crust illustrating the types of tectonic plates.
Illustration by José. F. Vigil 'This Dynamic Earth", Mural map produced jointly by U.S. Geological Survey, the Smithsonian Institution, and the U.S. Naval Research Laboratory.

Current provision of different tectonic plates

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Source: U.S. Geological Survey

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