Movements of Plates
Plate Tectonic theory is in the type of drift, with respect to the adjoining plates along the plate boundaries.
H.Hess produced the concept of plate tectonic in 1960 in support of continental drift. All the activities occur along the plate margin e.g. seismic events, volcanicity, mountain building, folding, faulting etc. Plate margin are generally divided into three main groups as follows
Constructive plate boundaries
Destructive plate boundaries
Conservative plate boundaries
Constructive Plate Boundaries
Constructive plate boundaries are also called is divergent plate boundary or accreting plate boundaries. This is a zone along with two plates are in the motion away from each other as a result of fisher developers, and create new margin. Infect oceanic plates split apart along the mid oceanic ridge and move in the opposite direction. The fissure represents the zone of spreading and created new crust by upwelling of material from the mental. It is the best example seen in the case of the North American plate versus Eurasian plate. Eurasian plate is moving away towards south east whereas North American plate is drifting towards south west.
Oceanic Divergent
The divergent plate boundary on the ocean floor is marked by the crust of the mid oceanic ridge. The existence of the Rift Valley at the ridge crest, associated with Basaltic lava. Volcanism appears to be the result of the ocean divergent. Eruption of the Lava creates new ocean floor within the Rift Valley.
Continental divergent
This is also known as continental ruptures and causes elevations of continent,this column of hot molten rock is called mantle plume. Due to elevation the crust becomes thinner above the uplift and the tensional force cause the plate to fracture forming a rift valley along a central graben.
The volcanic country Iceland is a island located in the MID ATLANTIC RIDGE
Its believed that the mid Atlantic ridge which forms a major part of the sub oceanic ridge encircling to the globe from Arctic ocean to South Africa. This type of presses is sometimes also referred as sea floor spreading.
some scientist have postulated development of new spreading centers under the African plate along the East African rift zone.
Destructive Plate Boundaries
Destructive plate Boundaries are also called as convergent plate or consuming plate boundaries because two plates move towards each others and leading edge of one plate overrides the other plate and the overridden plate is subducted into the mantle and thus part of the is lost in mantle.There can be three types of situations as
- Ocean -ocean convergence
- Continent-continent convergence
- Ocean -continent convergence
Ocean -Ocean Convergence
Two oceanic crusts converge and one plate bends down ward beneath the other. This phenomenon is called Subduction. Subduction of plate forming the oceanic crust is cause of the trench which is formed immediately over the zone of subduction.the magma bodies rise slowly to the surface forming a curved line of volcanoes which form a string of volcanic island knows as island arc.
Examples: The deepest Trench is located at the southern ssubduction end of the Mariana Trench caused by the convergence of Pacific plate.
Ocean-Continent Convergence
A plate containing the oceanic crust is subducted under the continental crust because it's less dence comparitivily oceanic crust. Magma that rises from the subduction zone and forms a Volcanic arc. But the continental crust remains intact and with the upward rising of hot magma from the subduction zone becomes thicker and formed a young mountain range.
The Peru Chile trench developed of the South America coast line is described as a typical example of subtraction.
- The South America Continental plate supporting the high range of Andes mountain is considered a proof enough for this typical case.
Continental -Continental Convergence
Two continents move towards each others and the leading edge of the both plates are composed of Continental rock, it is more difficult for subtraction to start. in this case a continental collision boundary may develop, in which the edges of the plates crumpled into mountains. this type of convergent boundary condition has produced some of the highest linear mountain system on the earth, such as Alpine in Himalayan mountain belts.
Conservative Plate Boundaries
These are also called as share plate margin and transform boundaries or transform fault. Here two plates pass or slide past one another along transform faults and this crust is neither created or destroyed. most such boundaries occur in Oceanic crust but some occur on continents are well known Continental transform boundary is the
San Anderson fault in California Where are segment of the Pacific plate is sliding horizontally past assignment of North American plate
Mineralization along different Boundaries
Deposit at Convergent Boundaries
- Deposits(Zn,Pb,Ag) are related to subtraction in the Western United State during cretaceous to middle tertiary.
-
Cu, Fe, No, Au and Ag are closely associated with calkaline magnetism in such zone.
- The tin tungsten belts of Bolivia, East India archipelago( an areas encompasses twelve seas, two gulfs, and one strait in the East Indies) and South China are located along similar tectonic setting.
Deposits a Divergent Plate Boundaries
- An example of recent thermal plume(rising air in the lower altitudes of the Earth's atmosphere)generated rift in Red Sea.
- Valley of the Red Sea has given rise to a number of a hot spring pools.
- Sulfide deposits and metallic deposits Fe, In, Cu, Pb, Au and Ag are formed.
Deposits at along Transform Fault
-
The coast range of California also host late Cenozoic Mercury deposits.
- McLaughlin hotspots gold deposit in California coast ranges.
- Salton sea geothermal system of the Imperial Valley California has a significant energy potential.
The hypothesis suggests that the mountain range were initiated and developed due to the convection currents supported to the exist in the plastic - type mental blow the crust of the earth. The origin of the currents may be due to very hot liquid core of the Earth. Some phenomena of convection currents are given below :
