Lithospheric plates of the Earth are enormous boulders.They formed the foundation of much crumpled into folds granite metamorphosed igneous rocks.The names of the lithospheric plates are given in the article below.From above they are covered with three-chetyrehkilometrovoy "cover."It is formed from sedimentary rocks.The platform has a relief consisting of individual mountain ranges and vast plains.Next will be considered the theory of plate movements.
emergence of hypotheses
Theory of plate movements emerged in the early twentieth century.Subsequently, she was destined to play a major role in the research world.Scientific Taylor, and after him, and Wegener hypothesized that over time there is a drift of lithospheric plates in the horizontal direction.However, in the thirties of the 20th century it confirmed a second opinion.According to him, the movement of the lithosphere plates carried out vertically.At the heart of this phenomenon lay the differentiation of mantle material world.It became known as fiksizmom.This name was due to the fact that the recognized permanently fixed position relative to the mantle areas of the cortex.But in 1960, after the discovery of a global system of mid-ocean ridges that encircle the planet and go into some parts of the land, there was a return to the hypothesis of the early 20th century.However, the theory has found a new form.Tectonics of the blocks was the leading hypothesis in science, studying the structure of the planet.
main provisions
It was determined that there are large lithospheric plates.Their number is limited.There are also lithospheric plates of the Earth smaller.The boundaries between them is carried out by condensation in earthquake.
names corresponding to the position of lithospheric plates over them continental and oceanic areas.Clumps of having a large area, a total of seven.The largest lithospheric plates - it's South and North American, Euro-Asian, African, Antarctic, Pacific and Indo-Australian.
lumps floating in the asthenosphere, different solidity and rigidity.The above areas - a major lithospheric plates.In accordance with the initial idea it was thought that the continents are making their way through the ocean floor.The motion of the lithosphere plates carried out under the influence of invisible forces.The studies revealed that the lumps floating passively on mantle material.It should be noted that their first vertical direction.Mantle material rises under the crest of the ridge top.It then spread to both sides.Accordingly, there is a divergence of lithospheric plates.This model represents the ocean floor as a giant conveyor belt.It comes to the surface in rift areas of mid-ocean ridges.Then, hiding in deep trenches.
The divergence of lithospheric plates provokes expansion of ocean lies.However, the scope of the planet, even though it remains constant.The fact that the birth of a new crust is compensated by its absorption in the areas of subduction (subduction) in deep-sea trenches.
Why does the movement of lithospheric plates?
reason is thermal convection of mantle material world.The lithosphere is subjected to tensile tests and the rise of what is happening on the ascending branches of the convective flows.This provokes the movement of lithospheric plates in hand.As the distance from the mid-ocean rift is compacted platform.It is heavier, its surface is lowered.This explains the increase in the oceanic depths.As a result, the platform is immersed in the trenches.When attenuation of ascending currents of heated mantle it cools and descends to the formation of pools that are filled with sediments.
Zone collision of lithospheric plates - are areas where the crust and the platform are compressed.In this regard, first power increases.As a result, it begins an upward movement of the lithospheric plates.It leads to the formation of mountains.
Research
Learning today carried out using geodetic methods.They suggest a continuity and ubiquity processes.Identified as areas of collision of lithospheric plates.Lifting speed can be up to ten millimeters.
Horizontal major lithospheric plates float somewhat faster.In this case, the speed can be up to ten centimeters during the year.So, for example, St. Petersburg has risen a meter for the entire period of its existence.Scandinavian Peninsula - 250 m 25 000 years.Mantle material moves relatively slowly.However, as a result of earthquakes, volcanic eruptions and other phenomena.This leads to the conclusion that high-power movement of the material.
Using tectonic plates position, the researchers explain the variety of geological phenomena.At the same time in the study it was found out much more than it first appeared at the beginning of the emergence of the hypothesis, the complexity of the processes occurring with the platform.
Plate tectonics could not explain the changes in the intensity of deformation and movement, the presence of a global sustainable network of deep faults and some other phenomena.It also remains an open question about the historical beginning of the action.Direct signs of a plate-tectonic processes are known from the period of Late Proterozoic.However, a number of researchers to recognize their manifestation Archean or Early Proterozoic.
Empowering research
seismic tomography appearance of this science led to the transition to a qualitatively new level.In the mid-eighties deep geodynamics has become the most promising young and direction of all existing earth sciences.However, new challenges carried out using not only the seismic tomography.Came to the aid and other sciences.These include, in particular, include an experimental mineralogy.
Thanks to the new equipment the opportunity to study the behavior of materials at temperatures and pressures corresponding to the maximum at the depths of the mantle.It is also used in the study of isotope geochemistry.This science studies, in particular isotope balance of rare elements, as well as noble gases in various terrestrial shells.This performance compares with meteoritic data.Geomagnetism applied methods by which scientists are trying to uncover the causes and mechanism of reversals in the magnetic field.
modern picture
tectonics hypothesis platform continues to satisfactorily explain the development of the cortex oceans and continents for at least the last three billion years.At the same time, there are satellite measurements, in accordance with which confirmed the fact that the major lithospheric plates of the Earth is not standing still.As a result, a definite picture emerges.
In cross-section of the planet there are three of the most active layer.The capacity of each of them is a few hundred kilometers.It is assumed that the main role in the global geodynamics entrusted on them.In 1972, Morgan has proved launched in 1963, Wilson hypothesis about the rising plume.This theory to explain the phenomenon of intraplate magnetism.The resulting plume tectonics over time becomes more and more popular.
Geodynamics
With the help of the interaction of quite complex processes that occur in the mantle and crust.In accordance with the concept set out Artyushkova in his work "Geodynamics", as the main source of energy in favor gravitational differentiation substance.This process is observed in the lower mantle.
Once separated from the rock heavy components (iron, etc.), is lighter weight solids.It falls into the kernel.Location easier under a heavy layer is unstable.Therefore accumulating material is collected periodically in a sufficiently large blocks, which emerge in the upper layers.The size of these formations is about one hundred kilometers.This material became the basis for the formation of Earth's upper mantle.
lower layer probably represents undifferentiated primary substance.During the evolution of the planet due to the lower mantle is a growth and an increase in the upper core.It is more likely that the blocks of light material in the lower mantle rise along the channels.They mass temperature is high enough.Viscosity thus substantially reduced.Increase in temperature promotes the release of a large amount of potential energy during ascent substance to gravity at a distance of about 2000 km.In the course of movement along this path is a strong heating of the lung mass.In connection with this substance enters into the mantle, having a sufficiently high temperature and significantly less weight in comparison with the surrounding elements.
by lowering the density of light material floats to the upper layers to a depth of 100-200 kilometers and less.With decreasing pressure drops melting point component substances.After the initial differentiation at the level of "core-mantle" comes secondary.On the shallow part of a light material is melted.Differentiation allocated denser substance.They are immersed in the lower layers of the upper mantle.Evolved lighter components, respectively, rise up.
complex movements in the mantle of substances associated with the redistribution of masses having different densities as a result of differentiation, a chemical called convection.Lifting lung masses occurs at a frequency of about 200 million years.At the same time the introduction of the upper mantle is not universally observed.In the lower layer channel are located at a greater distance from each other (to several thousand kilometers).
rise blocks
As mentioned above, in those areas where the introduction of large masses of light heated material into the asthenosphere, it is a partial melting and differentiation.In the latter case there is the selection of components and their subsequent ascent.They quickly enough pass through the asthenosphere.Upon reaching the lithosphere their speed is reduced.In some areas, the substance forms a cluster of anomalous mantle.They occur, usually in the upper layers of the planet.
anomalous mantle
Its composition corresponds approximately to the normal mantle material.The difference is the abnormal accumulation of a higher temperature (up to 1300-1500 degrees) and reduced speed of elastic longitudinal waves.
Receipt substance under the lithosphere triggers isostatic uplift.Due to the high temperature anomaly cluster has a lower density than the normal mantle.In addition, there is a small viscosity of the composition.
In the process proceeds to the lithosphere of the anomalous mantle rather quickly spread along the base.However, it displaces more dense and less heated material of the asthenosphere.In the course of the anomalous traffic congestion fills in those areas where the sole platform is in an elevated state (traps), and deep diving area, it wraps around.As a result, in the first case there is isostatic uplift.Above the submerged areas of the cortex remained stable.
traps
process of cooling the upper layer of the mantle and the crust to a depth of about one hundred kilometers is slow.In general, it takes several hundreds of millions of years.In connection with this heterogeneity in the thickness of the lithosphere is explained by horizontal temperature differences, they have a fairly high inertia.In the event that a trap is located not far from the abnormal accumulation upstream from the depths, a large amount of the substance is trapped very hot.This results in a fairly large element of the mountain.Under this scheme come up high in the area in the epi-platformal orogenic fold belts.Description
processes
Trapped anomalous layer during cooling is compressed by 1-2 kilometers.Bark, located on top, sinks.In the formed basin rainfall begin to accumulate.They contribute to the severity of the lithosphere sinking further.As a result, the depth of the pool can be from 5 to 8 km.With this compaction of the mantle in the lower portion of the basalt layer in the crust can be observed in the phase transformation of rocks and eclogite garnet granulite.Due to abnormal substances coming out of the heat flow occurs heating of the overlying mantle and lowering its viscosity.In this regard, there is a gradual replacement of normal accumulation.
horizontal displacement
The formation of uplifts in revenue anomalous mantle to the crust on the continents and oceans is an increase in the potential energy stored in the upper layers of the planet.To reset the excess of matter tend to disperse to the sides.As a result, additional stresses are generated.They relate different types of plate motion and bark.
Sprawl ocean floor and swimming continents are the result of the simultaneous expansion of ranges and dive platform mantle.Under the first there are large masses of intensely heated anomalous substances.The axial part of the last ridges located directly beneath the bark.Lithosphere here has a much smaller capacity.Anomalous mantle while spreads in the area of high pressure - in both directions from the ridge.At the same time, it is easy enough breaks the crust of the ocean.A cleft is filled with basaltic magma.She, in turn, is smelted from the anomalous mantle.In the process of solidification of magma formed a new oceanic crust.This happens floor spreading.
Features of
By mid-ocean ridges anomalous mantle has a reduced viscosity due to high temperature.The substance is able to spread fast enough.Therefore floor spreading occurs at an increased rate.The relatively low viscosity also has oceanic asthenosphere.
main lithospheric plates of the Earth ranges from sailing to the dive site.If these areas are in the same ocean, the process takes place at a relatively high speed.This is the case today for the Pacific.If the floor spreading and dipping takes place in different areas, located between the continent drifts in the direction where the groove.Under the continents the asthenosphere viscosity higher than under the oceans.Due to some friction resistance movement appears considerable.This reduces the rate at which the expansion of the bottom, if there is no compensation for dipping mantle in the same area.Thus, growth of the Pacific is faster than in the Atlantic.
