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Plate tectonic theory (English: Plate tectonics) is a theoryin the field of geology that was developed to provide an explanation for the existence of evidence of large -scalemovement by the Earth'slithosphere . This theory has been included and also replaces the theory of continental shifts which first put forward in the first half of the 20th century and the concept of seafloor spreading developed in the 1960s.

The outer portion of Earth's interior is formed from two layers. At the top there is the lithosphere consists of crust and upper mantle section is rigid and solid. Under layers of the lithosphere asthenosphere which there is solid but can flow like a liquid with a very slow and the geological time scale is very long because the viscosity and shear strength (shear strength) is low. Deeper, the mantle below the asthenosphere are becoming more rigid again. The cause is not a cooler temperature, but high pressure.

Lithospheric layer is divided into tectonic plates (tectonic plates). On earth, there are seven major plates and many of the plates which is smaller. These lithospheric plates ride on top of the asthenosphere. They are moving relative to each other at plate boundaries, both divergent (away), convergent (collide), or transform (sideways). Earthquakes, volcanic activity, mountain formation, and formation of oceanic trenches are all generally occur in areas along the plate boundaries. Lateral movement of plates is usually speed 50-100 mm / a.

Growth Theory

At the end of the 19th century and early 20th century, geologists assumed that the appearance of the main appearance of the earth-based equipment. Most of the geological appearance as the mountains can be explained by vertical crustal movements as described in the theory geosinklin. Starting in 1596, has been observed that the Atlantic Ocean coast of face to face between the continents of Africa and Europe with North America and South America have similar shapes and seem to never become one. This accuracy will be more obvious if we look at the edges of continental shelf there. Since then many theories have been advanced to explain this, but all were deadlocked because of the assumption that the earth is completely solid trouble finding a suitable explanation.

The discovery of radium and heating properties in 1896 to encourage a review of age of the earth, because of previous estimates obtained from the rate of cooling and assuming the Earth's surface radiated like a black body. From these calculations it can be concluded that even if at first earth is a red-fluorescent objects, the Earth's temperature will have dropped to as it is now within a few hundred million years. With the newly discovered source of heat is so the scientists think it makes sense that the Earth is actually much older and its core is still hot enough to be in a liquid state.

Plate Tectonic Theory comes from the shift hypothesis Continent (continental drift), Alfred Wegener put forward in 1912. and further developed in his book The Origin of Continents and Oceans, published in 1915. He suggested that the continents that now there was once a front landscape that is moving away thus releasing the continents from the core of the earth as 'iceberg' of the granite mass of low types that floats above the denser ocean basalt. However, the absence of detailed evidence and calculation of the forces involved, this theory is marginalized. Maybe the earth has a solid crust and liquid core, but it still seems unlikely that the parts of the crust to move. Later, the theory put forward dibuktikanlah British geologist Arthur Holmes in 1920 that links the parts of the crust is likely to exist under the sea. Also proved his theory that convection currents within the Earth's mantle is the driving force. The first evidence that the plates did have movement invention is obtained from the different directions of the magnetic field in rocks of different age. This discovery was first expressed at a symposium in Tasmania in 1956. At first, this invention is inserted into the earth expansion theory, but subsequently more precisely leads to the development of plate tectonic theory that explains the expansion (spreading) as a consequence of vertical movement (upwelling) of rock, but avoid the necessity of the earth continues to grow in size or expanding (expanding earth) by entering the subduction zone / hunjaman (subduction zone), and fault translation (translation fault). At that time the theory of plate tectonics changed from a radical theory into the theory of commonly used and widely accepted among scientists. Further research on the relationship between seafloor spreading and magnetic reversal of the earth (geomagnetic reversal) by geologist Harry Hammond Hess and Ron G. oseanograf Mason shows the exact mechanism by which explains the vertical movement of the new rock.
Along with the receipt of the earth's magnetic anomaly as indicated by the lane-lane parallel to the symmetrical with the same magnetization on the seafloor on either side of mid-oceanic ridges, plate tectonics became widely accepted. Rapid advances in seismic imaging techniques initially in and around Wadati-Benioff zone and various other geologic observations soon confirmed as the theory of plate tectonics that has tremendous capability in terms of explanation and prediction.
Research on the sea floor in, a branch of the rapidly growing marine geology in the 1960s plays an important role in the development of this theory. Correspondingly, plate tectonic theory is also developed in the late 1960s and has been pretty universally accepted in all disciplines, as well as updating the world geography by giving an explanation for the wide range of geological phenomena and their implications in other fields such as paleogeografi and paleobiology .

Main Principles

The outside of Earth's interior is divided into lithosphere and asthenosphere based on differences in the occurrence of mechanical and heat transfer. Lithosphere is cold and stiff, while the asthenosphere is hotter and mechanically weaker. In addition, the lithosphere loses heat through conduction process, whereas the asthenosphere also transfers heat by convection and has a nearly adiabatic temperature gradient. This division is very different from the chemical division of earth into core, mantle, and crust. Lithosphere includes the crust and also own a portion of the mantle. A part of the coat could have been part of the lithosphere or the asthenosphere at different times, depending on the temperature, pressure, and shear strength. Key principle is that the lithospheric plate tectonics separated into tectonic plates that is different. These plates move ride on top of which has a viscoelastic asthenosphere which is like a fluid. Plate movement can usually reach 10-40 mm / a (as fast as a fingernail growth) as in the Mid-Atlantic Ridge, or reaches 160 mm / a (as fast as the hair growth) as the Nazca Plate. Plate-Plate This about 100 km thick and consists of coat litosferik on which is coated with a stretch of one of two types of crustal material. The first is the oceanic crust or often called "sima", a combination of silicon and magnesium. The second type of continental crust that is often called "bad luck", a combination of silicon and aluminum. Both types of crust thickness is different in terms of where the continental crust has a thickness that is much higher than the oceanic crust. The thickness of continental crust reaches 30-50 km, while oceanic crust is only 5-10 km.
Two plates will meet along the plate boundary (plate boundary), which is an area where geological activity like earthquakes generally occur and the formation of topographical appearance such as mountains, volcanoes and oceanic trenches. Most active volcanoes in the world is above the plate boundaries, such as the Pacific Ring of Fire (Pacific Ring of Fire) on the Pacific Plate is the most active and widely known.
Plate tectonics may be a continental or oceanic crust, but usually one plate consists of both. For example, the African Plate includes the continent itself and most basic Atlantic and Indian Ocean. The difference between continental and oceanic crust is based on the density of its constituent materials. Oceanic crust is more dense than continental crust due to differences in the ratio of various elements, especially silicon. Oceanic crust is more dense because of its composition which contains less silicon and more serious material. In this case, the oceanic crust is said to be more than felsik mafik. Thus, the oceanic crust is generally located below sea level like most of the Pacific Plate, whereas continental crust occur over the sea surface, following a principle known as isostacy.

Types of Plate Boundaries

There are three types of plate boundaries are different from the way the plates are moving relative to one another. These three types are each associated with different phenomena on the surface. Three types of plate boundaries are:

    1. Limits transform (transform boundaries) occur when plates move and experiencing friction with each other laterally along the transform fault (transform fault). Relative movement of the two plates can be sinistral (left on the side opposite the observer) or dekstral (to the right on the side opposite the observer). Examples of this type of fault is the San Andreas Fault in California.
    2. Limits diverging / Constructive (divergent / Constructive boundaries) occurs when two plates move away from one another. Mid-oceanic ridges and fracture zones (rifting) enabled are examples of divergent boundaries
    3. Limits convergent / destructive (convergent / destructive boundaries) occurs when two plates rub against each other approached to form a subduction zone if one plate moves under another, or continent collision (continental collision) if the two plates contain continental crust. Deep ocean trench usually located in the subduction zone, where the pieces of plate which contains a lot of character terhunjam hydrate (containing water), so that the water content is released when heating occurs mixed with the mantle and cause melting, causing volcanic activity. Examples of this case we can see in the Andes Mountains in South America and the island arc of Japan (Japanese island arc).

Drive Strength Plate Movement

Tectonic plate movement can occur because of the relative density of oceanic lithosphere and the asthenosphere is relatively weak character. The release of heat from the mantle has been found as the original source of energy that drives plate tectonics. This view is approved now, though still quite debatable, is that the excess density of oceanic lithosphere that made infiltrate downward in subduction zones is the strongest source of plate movement. At the time of its formation in mid-ocean ridge, oceanic lithosphere initially have a lower density of the asthenosphere in the vicinity, but this density increases with aging due to the cooling and thickening. The amount of the old lithospheric density relative to the underlying asthenosphere allows the intrusion into the mantle at subduction zones so that the source of most of the driving forces of plate movement. The weakness of the asthenosphere allows the plates to move easily towards a subduction zone Although subduction is believed to be the strongest force driving plate movement, there is another driving force plate as evidenced by the North American plate, Eurasian plate is moving but not experienced subduction anywhere. Driving source is still a topic of intense research and discussion among scientists of the earth sciences. Two-and three-dimensional imaging of Earth's interior (seismic tomography) shows a heterogeneous density distribution laterally across the mantle. Variations in density may be material (from rock chemistry), mineral (from variations in mineral structures), or thermal (through thermal expansion and contraction from heat energy). Manifestation of lateral density heterogeneity is mantle convection from buoyancy (buoyancy forces) How mantle convection relates directly and not with the movement of planets is still a field that is being studied and dibincangkan in geodinamika. In one way or another, this energy must be transferred to the lithosphere to tectonic plates move. There are two main types of styles in its influence to the movement of planets, namely friction and gravity.

Scratch Style

Basal drag
Large-scale convection currents in the upper mantle asthenosphere distributed through, so that movement is driven by friction between the asthenosphere and lithosphere.Slab suction
Local convection currents provide downward pull on plates in subduction zones in oceanic trenches. Penyerotan slab (slab suction) can occur in conditions where the pull of basal geodinamik continue working on this plate at the time he entered into the mantle, although actually pull more work on both sides of the plate, the upper and lower

Gravity

Gravitational collapse: The movement of the plate occurs due to higher plate in oceanic ridge. Cold oceanic lithosphere becomes denser than the hot mantle, which is the source, then with increasing thickness of this plate sinks into the mantle to compensate the weight, resulting in less lateral inclination proportional to the distance from this axis. : In geology texts on basic education, the process is often referred to as a doronga. However, actually the more appropriate designation is the ruins because the topography of a plate can be very different and topographic ridge (ridge) that perform the expansion was the most dominant feature. For example, swelling of the lithosphere before he fell to the bottom plate adjacent to generate appearance could affect the topography. Then, the mantle plume that hit the underside of tectonic plates can also change the topography of the ocean floor.

Slab-pull (pull slabs)

Plate movement is also partly caused by a heavy plate of cold and dense that fell into the mantle at oceanic trenches. There is considerable evidence that convection also occurs in the mantle with a large enough scale. Upward movement of material in mid-oceanic ridge is probably part of this convection. Some early models of plate tectonics suggests that these plates riding on top of cells like conveyor belts. However, most scientists now believe that the asthenosphere is not strong enough to directly cause movement by the friction forces. Slab pull itself is very likely become the largest force acting on the plate. Newer models also provide an important role in penyerotan (suction) at the trough, but the plate as the North American Plate subduction did not experience anywhere else, but also experienced the movement as well as the African Plate, Eurasian, and Antarctica. The main driving force for plate movement and the energy source itself is still a matter of ongoing research

Styles from outside

In a study published in the January-February 2006 edition of the Bulletin Geological Society of America Bulletin, a team of scientists from Italy and the United States believes that the plate component that leads to the west came from the Earth's rotation and friction pairs of the month that follows. They said because the Earth rotates eastward beneath the moon, the moon, although very small gravitational pull of the earth layer permuikaan back to the west. Some also argued the controversial idea that this result may also explain why Venus and Mars has no plate tectonics, namely the absence of the moon on Venus and Mars to the small size of the moon like a tidal effect on Earth. The idea itself is actually not new. This in itself originally put forward by the father of this hypothesis itself, Alfred Wegener, and then challenged physicist Harold Jeffreys who calculated that the amount of friction required oasang will quickly bring the rotation of the earth to stop since a long time. Many plates are also moving north and west, even the number of movements to the western Pacific Ocean is the base when viewed from the perspective of the central division (spreading) in the Pacific Ocean that leads to the east. It also said that relative to the mantle below, there are few components that leads to the west on the movement of all plates

Relative significance of each mechanism

The actual vectors on the movement of a planet should be a function of all the forces acting on the plate. However, the problem is how much each process taking part in the movement of each plate Diversity geodinamik condition and nature of each plate should make a difference in how these processes are actively moving the plate. one way to overcome this problem is to look at the rate at which each plate moves and consider the evidence available for each driving force of this plate as far as possible. One of the most important relationship that was found was that of a sticky plate litosferik tersubduksi on plates that move much faster than plates that do not. For example, surrounded by the Pacific Plate subduction zone (Ring of Fire) that moves much faster than the sticky plate in the Atlantic on the adjacent continent and not a plate tersubduksi. Thus, the force that berhubungkan with plates that move down (slab pull and slab suction) are the driving force that determines the movement of plates except for plate that is not disubduksikan. While however, the driving force plate movement itself is still a matter of debate and research scientists

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