The Theory of Plate Tectonics

The theory of plate tectonics (English : Plate Tectonics ) is a theory in the field of geology developed to explain the evidence of large -scale movements performed by the lithosphere of the earth . This theory has also replaced the cover and continental shift theory is first put forward in the first half of the 20th century and the concept of seafloor spreading were developed in the 1960s .
Outermost part of the Earth's interior is made up of two layers . At the top there is the lithosphere consists of the crust and the upper part of the mantle is rigid and solid . Beneath the layers of the lithosphere asthenosphere are solid but can flow like a liquid with a very slow and in the geological time scale is very long due to the viscosity and shear strength (shear strength ) is low . Deeper , part of the mantle below the asthenosphere is more rigid nature become again . The cause is not the cooler temperatures , but high pressure .
Layers of lithosphere is divided into tectonic plates ( tectonic plates ) . On Earth , there are seven major plates and many plates smaller . The lithospheric plates ride on top of the asthenosphere . They are moving relative to each other in the plate boundaries , either divergent ( away ) , convergent ( colliding ) , or transform ( sideways ) . Earthquakes, volcanic activity , mountain-building , and oceanic trench formation generally occurs in areas all along the plate boundaries . The lateral movement of the plates is typically 50-100 mm speed / a. [ 1 ]

The development of theoryMaps with details that indicate tectonic plates and the direction of its motion vector
At the end of the 19th century and early 20th century , geologists assumed that the appearance of major earth - based permanent appearance . 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 Ocean coast of the face-off 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 there . [ 2 ] Since then many theories have been advanced to explain this , but everything is at a stalemate due to the assumption that the earth is completely solid complicate the discovery of appropriate explanations . [ 3 ]
The discovery of radium and its heating properties in 1896 to encourage the review of the age of the earth , [ 4 ] having previously obtained estimates of the rate of cooling and assuming the Earth's surface radiated like a black body . [ 5 ] From these calculations it can be concluded that even if at first the earth is an object that is red - flare , the Earth's temperature to drop to as it is now in a few tens of million years . With the heat source of this newfound scientists consider it absurd that the Earth is actually much older , and its core is still hot enough to be in a liquid state .
The theory of plate tectonics shift hypothesis comes from the Continent ( continental drift ) Alfred Wegener proposed in 1912. [ 6 ] and developed further in his book The Origin of Continents and Oceans , published in 1915 . He suggested that the continents are now there once was a face that moves away landscapes thus releasing the continents from the Earth 's core as ' iceberg ' of a low type of granite that mass floating on a sea of ​​denser basalt . [ 7 ] [ 8 ] However , in the absence of detailed evidence and calculation of the forces involved , this theory marginalized . Maybe Earth has a solid crust and a liquid core , but it still seems unlikely that the parts of the crust could move . Later, the theory proposed dibuktikanlah British geologist Arthur Holmes in 1920 that link parts of the crust under the ocean possibilities . Also proved his theory that convection currents in the Earth's mantle is the driving force . [ 3 ] [ 9 ] [ 10 ]
The first evidence that the plates did have movement obtained from the discovery of differences in the magnetic field direction in rocks of different age . This discovery was first revealed at a symposium in Tasmania in 1956. At first , the invention is incorporated into the theory of earth expansion , [ 11 ] but more precisely later lead 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 continues to grow in size or expansion ( expanding earth ) by entering the subduction zone / hunjaman ( subduction zone) , and cesarean translation ( translation fault ) . At that time the theory of plate tectonics changed from a radical theory becomes a theory commonly used and later widely accepted among scientists . Further research on the relationship between seafloor spreading and the Earth's magnetic field reversal ( geomagnetic reversal ) by geologist Harry Hammond Hess and Ron G. Mason oseanograf [ 12 ] [ 13 ] [ 14 ] [ 15 ] shows the exact mechanisms that explain the vertical movement of rock The new .
Along with the receipt of the Earth's magnetic anomaly indicated by parallel rows of symmetrical with similar magnetization on the seafloor on either side of the mid -oceanic ridge , plate tectonics became widely accepted . Rapid advances in seismic imaging techniques initially in and around Wadati - Benioff zones and a variety of other geological observation was soon confirmed as the theory of plate tectonics that have exceptional ability in terms of explanation and prediction .
Research on the deep ocean floor , 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 developed in the late 1960s and has been fairly universally accepted in all disciplines , as well as renew the world of earth sciences by providing an explanation for a wide range of geological phenomena and their implications in other fields such as paleogeography and paleobiology .Key Principles
Part of the outer layer , the interior of the Earth is divided into layers of the lithosphere and the asthenosphere layer based on differences in mechanical and heat transfer of the occurrence . Llitosfer more cold and rigid , while the asthenosphere is hotter and mechanically weaker . In addition , the lithosphere loses heat by conduction , 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 the earth into a core , mantle , and crust . Lithosphere includes the crust and also own a portion of the mantle .
A portion of the mantle may be part of the lithosphere or the asthenosphere at different times , depending on the temperature , pressure , and shear strength . Key principle of plate tectonics is that the lithosphere separated into tectonic plates different . This slab moves over the asthenosphere ride that has so behave like viscoelastic fluid . The movement of the slab could reach 10-40 mm / a ( fast as fingernails grow ) as in the Mid-Atlantic Ridge , or can reach 160 mm / a ( fast hair growth ) as the Nazca Plate . [ 16 ] [ 17 ]
These plates about 100 km thick and consist of lithospheric mantle on which is coated with a stretch of one of two types of crustal material .The first is the oceanic crust or often called the " sima " , a combination of silicon and magnesium .The second is the continental crust that is often called " bad luck " , a combination of silicon and aluminum .
The two types of crust differ in terms of thickness where the continental crust has a thickness that is much higher than the oceanic crust . The thickness of the continental crust reaches 30-50 km while the oceanic crust is only 5-10 km .
Two plates will meet along the plate boundaries ( plate boundary) , which is an area where geological activity such as earthquakes generally occur and the formation of topographical appearance such as mountains, volcanoes and oceanic trenches . Most active volcano in the world is above the plate boundaries , such as the Pacific Ring of Fire ( Pacific Ring of Fire ) in the Pacific Plate 's most active and widely known .
Plate tectonics may be continental or oceanic crust , but usually one plate consists of both. For example , the African Plate includes the continent itself and the base portion of the Atlantic Ocean and the Indian .
The difference between the continental crust by oceanic crust is based on the density of the constituent material .

    Oceanic crust is denser than continental crust due to differences in the comparison of the various elements , especially silicon .

    Continental crust is denser because the composition contains less silicon and more heavier material . In this case , the oceanic crust is said to be more mafic than felsik . [ 18 ] Thus , oceanic crust generally lies below sea level as most of the Pacific Plate , while the continental crust is raised to above sea level , following a principle known as isostacy .
Types of Plate BoundariesThree types of plate boundaries ( plate boundary) .
There are three types of plate boundaries are different from the way the plates move relative to one another . These three types are each associated with different phenomena on the surface . Three types of plate boundaries are:

    Limit transform ( transform boundaries ) occur 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 to the observer ) or dekstral ( to the right on the opposite side of the observer ) . Examples of this type of fault is the San Andreas Fault in California .
    Limit divergent / constructive ( divergent / constructive boundaries ) occurs when two plates move away from each other . Mid -oceanic ridge and fracture zones ( rifting ) enabled is an example of a divergent boundary
    Limit convergent / destructive ( convergent / destructive boundaries ) occurs when two plates rub against each other approached to form a subduction zone when one plate moves under another , or a continental collision ( continental collision ) if the two plates contain continental crust . Deep ocean trenches usually located at a subduction zone , where the pieces of plate that has taken root contains many are hydrates ( containing water ) , so that the water content is removed when the heating occurs mixed with the mantle and lead to melting , causing volcanic activity . An example of this can be seen in the Andes Mountains in South America and the Japanese island arc ( Japanese island arc ) .
Strength Activator Plate Movement
The movement of the tectonic plates could occur due to the relative density of oceanic lithosphere and the asthenosphere is relatively weak character . The release of heat from the mantle has been found to be the original source of energy that drives plate tectonics . The views were approved today , although still quite debatable , is that excess density of the oceanic lithosphere makes infiltrate downward at subduction zones is the strongest source of slab movement .
At the time of its formation in the mid- ocean ridge , oceanic lithosphere initially has a lower density than the surrounding asthenosphere , but the density increases with aging due to the cooling and thickening . The magnitude of the density of old lithosphere relative to the underlying asthenosphere allows the intrusion into the mantle at subduction zones so that the source of most of the driving force - plate movement . The weakness of the asthenosphere allows the plates to move easily towards a subduction zone [ 19 ] 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 , the Eurasian plate is also moving but did not experience subduction anywhere . Driving source is still a topic of intensive research and discussion among scientists in earth science .
Two and three -dimensional imaging of the Earth's interior ( seismic tomography ) shows heterogeneous density distribution throughout the mantle laterally . Variations in the density could be material ( from rock chemistry ) , mineral ( from variations in mineral structures ) , or thermal ( through thermal expansion and contraction from heat energy ) . Manifestations of heterogeneity in the lateral density is mantle convection from buoyancy ( buoyancy forces ) [ 20 ] How mantle convection relates directly and not by the movement of the planet into a field that is still being studied and dealt in geodynamics . With one way or another , this energy must be transferred to the lithosphere that the tectonic plates to move . There are two main types of styles in its influence to the movement of the planets , ie friction and gravity .Stringed style
basal drag
    Large-scale convection currents in the upper mantle asthenosphere distributed through , so that the movement is driven by friction between the asthenosphere and lithosphere .slab suction
    Provide local convection currents pull down on the plates in subduction zones at ocean trenches . Penyerotan slab ( slab suction ) can occur in conditions where traction geodinamik basal plates continue to work on this at the time he entered into the mantle , although actually pull more work on both sides of the plate , top and bottom
gravitation

    Debris gravity : plate movement occurs due to higher in oceanic ridge plate . Cold oceanic lithosphere becomes denser than the hot mantle is the source , then by increasing the thickness of the plate sinks into the mantle to compensate for weight, produces little lateral inclination proportional to the distance from the axis . : In geology texts on basic education , this process is often referred to as a doronga . However , the actual title is more appropriate because of the topography of a plate debris can be very different and dike topography ( ridge ) that performs the division is simply the most dominant feature . For example , swelling of the lithosphere before it fell to the bottom of the plate adjacent produce can affect the appearance of the topography . Then , press the side of the mantle plume under the tectonic plates can also change the topography of the ocean floor .Slab - pull (tension slab )
    Plate movement partly caused also by the weight of cold, dense plates descend into the mantle in the oceanic trenches . [ 21 ] There is considerable evidence that convection also occurs in the mantle with a large enough scale . Upward movement of the material in the mid -oceanic ridge is likely part of this convection . Some early models of plate tectonics suggests that these plates riding on top of the 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 themselves very likely to be the largest force acting on the plate . Newer models also provide an important role in penyerotan ( suction ) in the trough , but the slab as the North American Plate subduction not experience anywhere else , but also to have movement as well as the African Plate , Eurasian , and Antarctic . The main driving force for the movement of the slab and the energy source itself is still a matter of ongoing research
Outside force
In a study published in the January-February issue of 2006 of the bulletin of the Geological Society of America Bulletin , a team of scientists from Italy and the United States argued that the plate component that leads to the west comes from the Earth 's rotation and tidal friction months that followed . They said because the Earth spins eastward beneath the moon, the moon's gravitational pull is very small even though the Earth's surface layer back westward .
Some people also put forward controversial idea that these results may also explain why Venus and Mars does not have plate tectonics , ie in the absence of Venus and the moon in the small size of the moons of Mars to give effect to such tides on earth . [ 22 ]
This thought itself is actually not new . This in itself originally put forward by his own father of this hypothesis , Alfred Wegener , and then challenged physicist Harold Jeffreys who calculated that the magnitude of the frictional forces required oasang will quickly bring the Earth's rotation to stop since a long time .
Many plates are moving north and west , even many basic movement to the west is the Pacific Ocean from the point of view of the center of expansion ( spreading ) in the Pacific Ocean that leads to the east . It also said that relative to the lower mantle , there are fewer components that leads to the west on the movement of all platesThe relative significance of each mechanismPlate movement , based on NASA JPL GPS satellite data . Vector here indicate the direction and magnitude of movement .
Vectors are actually 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 to take part in the movement of each plate Diversity geodinamik conditions and properties of each plate should make a difference in how these processes are actively moving the plate . one way to overcome this problem is by looking at the rate at which each plate is moving and to consider the available evidence for each of the driving forces of plate as far as possible .
One of the most important relationships found is that lithospheric plates are sticky on the tersubduksi plates move much faster than plates that do not . For example , the Pacific Plate subduction zone surrounded ( Ring of Fire ) that move much faster than plates in the Atlantic are sticky on the adjacent continent and not a plate tersubduksi . Thus , the force berhubungkan with downward moving plate ( slab pull and slab suction ) are the driving force that determines the movement of the plates except for the plates were not disubduksikan . Although however, the driving force of plate movement itself is still a matter of debate and research scientistsMain platesMap of tectonic plates
Major tectonic plates namely :

    African Plate , covering Africa - Continental plate
    Antarctic Plate , covering Antarctica - the continent Plate
    Australian Plate , covering Australia ( fused with Indian Plate between 50 to 55 million years ago ) - Continental plate
    Eurasian plate , covering Asia and Europe - Continental plate
    North American Plate , covering North America and northeastern Siberia - Continental plate
    South American Plate , covering South America - the continental plate
    Pacific Plate , covering the Pacific Ocean - the ocean plate
Another important plates smaller include the Indian Plate , Plate Arabia , the Caribbean Plate , the Juan de Fuca Plate , Cocos Plate , Nazca Plate , Philippine Plate , and the Scotia Plate .
The movement of plates has caused the formation and breakdown of continents over time , including the formation of the supercontinent that includes most or all of the continents . Supercontinent Rodinia formed at roughly 1 billion years ago and covers most or all of Earth's continents , and broken up into eight continents around 600 million years ago . The eight continents later reorganized into another supercontinent called Pangaea , which also split into Laurasia ( which became North America and Eurasia ) and Gondwana ( which became the remaining continents )