Outermost part of Earth's interior is formed of two layers. At the top there lithosphere comprising the crust and upper mantle is rigid and solid. Under the layers of the lithosphere asthenosphere there is a solid but can flow like a liquid with a very slow and in a geological time scale is very long because the viscosity and shear strength (shear strength) is low. Deeper, the mantle below the asthenosphere is more rigid nature become again. The cause is not the cooler temperatures, but high pressure.
Layers of the lithosphere is divided into tectonic plates (Tectonic plates). On earth, there are seven major plates and many plates are smaller. These lithospheric plates ride on the asthenosphere. They move relative to each other at plate boundaries, both divergent (away), convergent (colliding), or transform (sideways). Earthquakes, volcanic activity, mountain formation, and formation of oceanic trenches are all generally occurs in areas along plate boundaries. Lateral movement of the plates is typically speed 50-100 mm / a.
A. Development of Theory
At the end of the 19th century and early 20th century, geologists assumed that the appearance of the main appearance of the earth-fixed domicile. Most geological appearance as mountains can be explained by vertical crustal movement as described in the theory geosinklin. Since 1596, it has been observed that the Atlantic coast that 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 the continental shelf in there. Since then many theories have been advanced to explain this, but all of a stalemate because of the assumption that the earth is fully dense complicate the discovery of an appropriate explanation.
The discovery of radium and heating properties in 1896 encouraged the review of the age of the earth, because previous estimates obtained from the cooling rate and assuming the earth's surface radiating like a black body. From these calculations it can be concluded that even if at first the earth was a red-glowing object, the temperature will fall to Earth as it is now within a few tens of millions of years. With the newly discovered source of heat is then the scientists think it makes sense that the Earth is actually much older and the core is still hot enough to be in the liquid state.
Theory of Plate Tectonics Hypothesis The shift comes from the Continent (continental drift) Alfred Wegener proposed in 1912. and developed again in his book The Origin of Continents and Oceans, published in 1915. He suggested that the continents that now there was once a landscape front that is moving away thus releasing the continents from the Earth's core as 'iceberg' of granite that low-mass type that floats on a sea of more dense basalt. However, in the absence of detailed evidence and calculation of the forces involved, this theory was marginalized. Perhaps the earth has a solid crust and liquid core, but still it does not seem possible that parts of the crust can be moving. Later, the theory put forward dibuktikanlah British geologist Arthur Holmes in 1920 that links 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 do experience gained from the discovery of differences in the movement direction of the magnetic field in rocks of different age. This discovery was first expressed at a symposium in Tasmania in 1956. At first, the invention is incorporated into the theory of Earth expansion, but later more precisely leads to the development of plate tectonic theory which explains the expansion (spreading) as a consequence of vertical movement (upwelling) rocks, but avoids the necessity of the earth whose size continues to grow or expand ( 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 theories which are commonly used and widely accepted among scientists. Further studies on the relationship between seafloor spreading and the reversal of the earth's magnetic field (geomagnetic reversal) by geologist Harry Hammond Hess and Ron G. oseanograf Mason pinpointing the mechanisms that explain the vertical movement of the new rock.
Along with the receipt of the earth's magnetic anomaly indicated by the lane-lane parallel to the symmetry with the same magnetization on the seafloor on either side of mid-oceanic ridge, plate tectonics became widely accepted. Rapid advances in seismic imaging techniques initially in and around Wadati-Benioff zones and various other geologic observations soon confirmed as the theory of plate tectonics that has a remarkable ability in terms of explanation and prediction.
Research on the seafloor, a branch of the rapidly growing marine geology in the 1960s played an important role in the development of this theory. Correspondingly, plate tectonic theory was also developed in the late 1960's and has been pretty universally accepted in all disciplines, as well as renew the earth sciences by giving an explanation for the wide range of geological phenomena and their implications in other fields such as paleogeografi and paleobiology .
B. Key Principles
Parts of the outer layer, the Earth's interior is divided into layers of the lithosphere and asthenosphere layer based on differences in the occurrence of mechanical and heat transfer. Llitosfer more cold and rigid, whereas 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 power sliding. Key principle of plate tectonics is that the lithospheric plates separated into different tectonic. These plates move a ride on the asthenosphere which has viskoelastisitas so it behaves like a fluid. The movement of the slab can reach 10-40 mm / a (growing as fast as your fingernails) as in the Mid-Atlantic Ridge, or can reach 160 mm / a (as fast hair growth) as the Nazca Plate.
These plates about 100 km thick and consists of a coat litosferik upon 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 is the continental crust is commonly called "unfortunate", 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. Continental crust thickness reaches 30-50 km whereas oceanic crust is only 5-10 km.
Two plates will meet along the plate boundary (plate boundary), ie areas 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 can be continental or oceanic crust, but usually one plate consists of both. For example, the African Plate includes the continent itself and in part the basis of the Atlantic and Indian Ocean.
The difference between the continental crust by oceanic crust is based on the density of its constituent materials.
• Oceanic crust is denser than continental crust due to differences in the comparison of various elements, especially silicon.
• Continental crust is more dense because the composition contains less silicon and more material by weight. In this case, said the oceanic crust is more mafic than felsik. Thus, oceanic crust generally lies below sea level like most of the Pacific Plate, while the continental crust occur over the sea surface, follow a principle known as isostasi
Types of Plate Boundaries
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| Three 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. Boundary transform (transform boundaries) occurs when plates move and experiencing friction with each other laterally along the transform fault (transform fault). The second plate relative motion 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. Limit divergent / constructive (divergent / constructive boundaries) occurs when two plates move away from each other. Mid-oceanic ridge and fracture zones (rifting) is an example of active divergent boundary
3. Limit convergent / destructive (convergent / destructive boundaries) occurs when two plates rub against each other so close 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 a subduction zone, where the pieces of plate which contains many are 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 these cases we can see in the Andes Mountains in South America and the island arc of Japan (Japanese island arc). Strength Activator Plate Movement
The movement of tectonic plates can occur because of the relative density of oceanic lithosphere and 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. The view is approved now, although still quite debatable, is that the excess density of oceanic lithosphere that makes infiltrate downward in subduction zones is the strongest source of the movement of the slab.
At the time of its formation in mid-ocean ridge, oceanic lithosphere initially have a lower density than the surrounding asthenosphere, but this density increases with aging due to cooling and thickening. Magnitude of the density of the old lithosphere relative to the underlying asthenosphere allows the infiltration into the deep mantle at subduction zones so that the source of most of the driving forces-the movement of plates. Weaknesses asthenosphere allows the plates to move easily towards a subduction zone. Although subduction is believed to be the strongest driving forces-the movement of plates, there are other driving forces as evidenced by the presence of the slab as the North American plate, Eurasian plate is also moving but did not experience anywhere subduction. Driving source is still a topic of intensive research and discussion among scientists of earth sciences.
Two-and three-dimensional imaging of the Earth's interior (seismic tomography) shows a heterogeneous density distribution throughout the mantle laterally. Variations in density may be material (from rock chemistry), mineral (from variations in the mineral structure), 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 relate directly and not by movement of the planet is still a field that is being studied and dealt in geodinamika. With one way or another, this energy must be transferred to the lithosphere to tectonic plate movement. There are two main types of styles in its influence to the movement of planets, ie friction and gravity.
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