Plate tectonics is a logical hypothesis that recognizes theextensive scale movements of Earth’s lithosphere. Where plate’s boundariescombine, the movement of these plates decides that what type of boundary formhere, Example convergence plate boundary, divergent plate margin, transforms margin.With these plate margins, Quakes, volcanoes, mountain-building, and Marinetrenches are associated. The horizontal relative development of the platesnormally shifts from zero to 100 mm every year.The Earth’s crust is divided into 12 plates which changes thereposition in various directions with the passage of time. The motion of theseplates causes, collision (collide each other), Pull apart or slide past withone another.
With plate interaction different type of geologic structures ortectonic feature are developed.Certaintheories of plate tectonic are present which explain that at ocean ridges theplates are generated and along Subduction zones the plate are consumed, andareas where transform fault present the plates are slide past each other andwhen two plates collision occur, then suturing of plates occur.Plate boundaries are classified into three types, on thebasis of motion relative toward one another.a. Convergent plate boundary: Oneplate plunges underneath another (Subduction) or two plates collide withouteither subductingb. Divergent plate boundary: New lithosphere forms as platespull apart.
c. Transform plate boundary: Plates grind past each other, nochange in Lithosphere.Thesethree plate boundaries have different type of stresses so as this yielddifferent structure. At divergent plate boundary extensional stresses are producedwhich make normal faults and graben which is uncommon. At transform plateboundary shear stresses produced which causes bending and fractures in the rock,fault, bending and uplift of rock occur. At convergent plate margin compressivestresses are produced, because of which folds, reverse fault and thrust faultare form.At convergent plate boundaries collision of two plate occurbecause of when two plates are moving towards each other.
In these boundariesthe heavier (Denser) plate drive undergo the less heavy (lighter) plate. Theprocess at which one plate drive underneath the other is known as Subduction,the plate which is going below the other are reach into the mantle and herethey melts because temperature is very high in the mantle.At convergence plate boundaries continuously new Lithosphereis produced occur along oceanic ridges, but there is no changing occur in theearth total volume. The volume of earth remains same as previous one (earthvolume remain constant). There is a cyclic process continue, the older oceaniclithosphere will go into the mantle as same rate as the rate of production ofsea floor.Subduction zones which is also known as Convergentboundaries. Subduction zones are the place where one plate is undergo beneaththe other (subducted) and will reach to the mantle. Subduction of two platesoccur when there is density contrast between the two plates for example theoceanic lithosphere is subduct below the continental plates because oceanicplates are denser than continental plate.
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The continental lithosphere is lessdense so there is no subduction occur and the oceanic plate will have highdensity and will subduct up to greater depth.Whenthe lithosphere having oceanic origin descend down and will go into mantle asurface like feature are produced called deep ocean trenches, these trenchesare in the form of long and deep depressions. Example Pero Chile trench whichis 4499 km in length and 7.9 km below sea level present along the west coast ofS.
America. Other example of western Pacific are Mariana trench and Tongatrench which are deeper than those which are present in the Eastern Pacific.Theoceanic plate slabs are goes down into the mantle with small angle or at 90degree. The angle downward movement is depend upon the density of the plate.
For example when the spreading zone is around the subduction zone along PeruChile trench, the subducting material are younger and are hot and floatingoutward. Here small angle of descent are form. Because of this the area aroundthe Peru Chile trench have large no of earthquakes i.e., 2010 Chile earthquakewhich is also included in top 10 largest recorded earthquake. Properties of allthe convergent plate boundaries are same and they have very complex structures.Each of these feature is form from different material and different tectonicenvironment.Whentwo ocean plate, or one continental and ocean plate or either two continentalplate meet or collide convergent boundaries are generated On the basis of thisthere are three type of convergent plate boundaries.
1. Oceanic-continentalconvergence2. Oceanic-Oceanicconvergence3. Continental-continentalconvergence Thisis the type of convergence in which one continental plate and one oceaniccollide by one another. In the convergent the plate consuming higher density(oceanic plate) goes down and reach into the mantle and the lesser densityplate (continental plate) floating. When these margins slabs reaches to themantle layer, they start melting of the block of asthenosphere, these processesoccur at a distance of 90-100 km.
.Inthat type of convergence partial melting of rock occur, which produced around11 percent molten material then these melted substances are mixed with mantlerock those which is not melted. When the oceanic plate goes downward, theycontain sediment which have high amount of water, these are derived fromoceanic crust, and the high pressure and temperature condition remove waterfrom the pore spaces. This process causes melting of rock which is calledpartial melting. These melting rock are less dense than the surrounding rocki.
e. mantle rocks so these material rises upward in the form of volcanoes, butall of these material not reaches to the surface and solidifies within theearth crust which causes the increase in the crust volume.Exampleof the above process is Andes Mountain, which is form from the subduction ofNazca plate below the South American plate, these are form from subduction ofoceanic lithosphere and known as continental volcanic arcs. Other examplesinclude the mountains of California contain Mount Rainer, Mount Shasta, andMount of St. Helens which is reach to the Canada and here it include MountGaribaldi, Mount Silverthorne and others.
Whentwo ocean plate are meet or collide each other, they form as oceanic-oceanicconvergence boundaries. Many feature which are produced along this type ofconvergence are commonly present in continental plate boundaries. At thisboundary also subduction of one plate occur which reaches into the mantle andtriggers volcanic activity, as same process which is occur alongcontinental-oceanic convergence boundaries.Thetwo ocean plate convergence setting, the volcanic activity generated from theocean floor. In this a chain of volcanic mountains are produced which is occurin large amount and form as Islands. These are called as volcanic Island arc orIsland arc.ExampleMariana and Tonga Islands (young island arc). The Island arc produced 99-301 kmfrom deep ocean trench.
The western pacific ocean contain most island arcs, theAtlantic Ocean contain only two island arcs. Antilles Island are form becauseof the subduction of the Atlantic beneath the Caribbean plate, present inUnited States, British virgin island and also present in Martinique islandexample of this is Mount Pelee which is erupted in 1902 as well as kill 28,000people.Theisland arc which is form newly have simple structure besides underlain byoceanic crust, commonly less than 21 km thick. And the older island arc havecomplex structures and are underlain by highly deformed crust which reaches to36 km in thickness. Examples Japan, Indonesia, and Philippines.
These islandarc are generated form early form island arc system. Thistype of convergent boundary is form from the collision of two continentalplates. In this type of boundary no subduction occur, because of this boundarymountain ranges are form. When the collision of two continental plate occur itwill causes the formation of folds and deform the sediment and sedimentary rockwhich is accumulate here along continental plate boundaries.
This collisioncauses the formation of high mountain ranges which is highly deformed andcontain sedimentary and metamorphic rocks.Exampleinclude the collision of indian plate and the Eurasisan plate, starts before51-60 million years ago, produced Himalayas, which is the very important andhave the world most highest peaks. In this collision the crustal shorteningoccur and increase in thickness takesplace.Otherexample include, Alps, Appalachians, and Urals which are also form as a resultof collision of two plates.This report is about the convergent plateboundaries, in which explain the formation of convergent plate boundary, howsubduction occur and how oceanic trenches are formed then explain the categoriesof convergence plate boundaries,Three distinctive types of convergent are recognized: (1) the convergence oftwo oceanic plates, (2) the convergence of a continental plate and an oceanicplate, and (3) the convergence of two continental plates.Convergentplate boundaries (continental-continental) is a place where two tectonic platesmeet each other.
All tectonic plates are constantly being moved because of theconvection currents that occur in the mantle. Continental plates are creatingmountains when they pushed into each other. A few examples of this feature arethe Himalaya Mountain Range and the Appalachian Mountain Range.Asubduction zone also develops where oceanic and continental plates converge.The less-dense continental crust always resists subduction into the densemantle and over rides the oceanic plate. Consequently, the volcanic arc formson the continent, and compression may deform the continental margin into afolded mountain belt.Thesimplest type of convergent plate boundary is ocean-ocean convergence which consistsof two oceanic plates.
As the plates collide, one is thrust under the otherforming a subduction zone. The subducting plate run down to the mantle, whereit is heated, starting the generation of magma. The magma, being less densethan the neighboring rocks, upsurges and blowup on the seafloor, ultimatelybuilding an arc of volcanic islands. Andesite is the volcanic rock thatcharacteristically forms at such sites.
