Principles of Plate Tectonic Movement Essay Example

to the tidal forces between moon and the sun.

Key principles

Asthenosphere and lithosphere are the major layers which forms the earth crust where the tectonic plates are suspended. The lithosphere part is in solid form and its temperature is low unlike the asthenosphere which is hot and exists in molten status(Runcorn, 2013). The two layers lose heat in different mechanisms that is, conduction and convention respectively. This contributes to the temperature gradient; however, this has not been confused with the scientific subdivision of chemical composition for the two layers.
The tectonic lithosphere is composed of two parts; the oceanic crust which is referred to as sima and the continental crust also known as sial which is made up of aluminum content. The thickness of oceanic crust is approximated to be 100km and it keeps varying depending of the age (Le Pichon et al, 2013). This thickness is estimated from the mid of the sea which grows at rate of 170 mm on annual basis. On the other side, the sima has a thickness of 200km. which also keeps on changing due to the factor of mountain ranges, basins and cratonic on the interior of continents.

The boundaries of the plates are associated with natural features such as volcanoes, mountains, ridges and other related features. In addition, geological occurrences such as earthquakes are common along the boundaries. Schmalholz (2014) explains that most of the tectonic plates contains the both oceanic and crust layers. For instance, the African plate covers both dry land of the continent and oceanic parts of Atlantic and Indian Oceans. The oceanic part of the crust forms the flow of the sea which is covered by

water while the continental crust part forms the dry land which is formed through tectonic processes (Einsele, 2013). Studies carried out by different researchers demonstrates that, the ocean crust is denser compared to the continental crust. The indifference in density is based on the material content of each layer, whereby silicon is lighter than aluminum on the continental crust.

Plate tectonic boundaries

The theory of continental drift explains the existence of three types of boundaries which have distinctive features. However, some boundaries have common characteristics due to the phenomenal existence.

Convergent boundaries

It is also known as destructive or active margin. This type of boundary occurs where the two tectonic plates move towards each other (Runcorn, 2013). The movement is a slide which is either continental collision or subduction zone where one plate is moving beneath each other. The common features which have been formed in this type of boundaries include; cascade mountains in united states and Andes in South Africa. The concept argues that, the denser lithosphere slides beneath the lighter plate of the continent. The slip causes the density gradient between the two layers (Runcorn, 2013). This causes development of earthquakes and deep forms of trenches leading to formation of arc like shape. The upper part of the mantle of the sub ducted tectonic plate heats up to develop magma hence forming series of volcanic mountains.

Transform boundaries

It is also referred as constructive boundaries and occurs where the two tectonic plates slides each other. A study by Runcorn, (2013) proved that, there is no formation of new features since there is neither destruction nor creation resulting from the sliding action. Transform fault is developed along the line of

slide, particularly across the spreading center. A good example of a feature developed in transform boundary is San Andreas Fault in United States.

Divergent boundaries

It is also referred as conservative since the plates are not damaged or destroyed. In the ocean zones, the divergent boundaries develop at the spreading seafloor which forms a depression basin hence expansion of the ocean bodies (Schmalholz, 2014). At extreme cases, the movement causes volcanoes and earthquakes.The common well known features associated with divergent boundaries include; East African rift valley, Red sea, Mid Atlantic ridge and East Pacific rise.

Driving forces of plate motion

Tectonic plates move due to relative density of oceanic lithosphere and the weakness of the asthenosphere (Kuzmin & Yarmolyuk, 2016). The heat that originates from the mantle is the original source of the energy that facilitates and drive to plate movement by either causing convection or large scale upwelling and doming. Plate movement is caused by excess density that results from the sinking of the oceanic lithosphere in a zone called subduction zone. After the formation of the new crust at mid-oceanic ridge initially results to less density thus the greater density from the old lithosphere in relation to the asthenosphere allows sinking o the mantle at the seduction zone hence triggering plate movement (Schmalholz, 2014).

Subduction is thought to be only the strongest driving force to plate movement though it there other plate which move and are not sub-ducted such as North America Plate and the Eurasian Plate. This therefore causes more concern to scientists be involved in intensive discussion and research. The driving forces can be generally divided and categorized in to three based on the movement;

Driving forces

related to gravity.

The forces related to gravity are caused by secondary phenomena within framework of general mechanisms as mantle dynamics (Kuzmin & Yarmolyuk, 2016). The motion of the plate is caused by elevation of plate at the oceanic ridge. When the oceanic lithosphere results in the spreading ridges from the materials of the hot mantle, gradual cooling and thickening with age occurs thus adding distance from the ridge (Schmalholz, 2014). The increase in thickness cause subsiding of the cool oceanic lithosphere which is denser than the materials on the hot mantle to compensate greater load that results. This causes lateral incline and slight increase of distance from the axis of the ridge.

The above force is called the ridge push and the mechanism is referred to as gravitational sliding since variable topography across the plates can vary yet it is the most prominent feature. Other mechanisms that results cause gravitational secondary force (ridge push), include flexural bulging of lithosphere before diving underneath the adjacent plate producing topographical features. Slab push is rigid or competed to causing direct motion by friction along the bases of the lithosphere. Plate motion is therefore driven the weight of cold and dense plate that sinks on the plate.

Driving force related to mantle dynamics

This is the main driving force behind the motions of the tectonic plate. It envisages large scale convection currents in upper mantle which is transmitted through the asthenosphere (Kuzmin & Yarmolyuk, 2016). Seismic tomography show that varying of the lateral distribution of density throughout the mantle. The density variation can be a result of material, mineral or thermal. Mantle convection from buoyancy forces is a manifestation of the varying

lateral density.
There are two main types of forces that influence the motion of the plates; basal drag (friction) and slab suction (gravity).Basal drag states plate motion is caused by friction between convection currents in asthenosphere and the overlying lithosphere. In terms of slab suction, plate motion is driven by the local convection currents exerting a pull downwards on the plate subduction zone in the oceanic trenches (Schmalholz, 2014). This can occur in geodynamic setting where basal traction acts on the plate as long as it dives into the mantle.

Driving forces related to Earth rotation.

The oceanic crust is thought to be in motion with the continent as a result Earth rotation. Popular known driving forces are; tidal drag which is as a result of gravitational force of the moon and the sun exerted on the Earth’s crust, global deformation of the earth shape due to displacement of the rotational pole in relation to the crust of the Earth and other deformation effects on the crust due to spinning and wobbles movements of Earth’s rotation. The small negligible forces that cause rotation of the earth are; Coriolis forces and the Centrifugal forces which is treated as a small gravity modification (Kuzmin & Yarmolyuk, 2016).

Tectonic movement theory

It was modified by Alfred Wegner in 1912 and referred it to as continental drift in his book called “the origin of continents and oceans.” The development theory states that at the beginning there existed a one mass land known as Pangaea that drifted to form continents(Le Pichonet al, 2013). It divided into two parts and this is proved by the contiguous nature of the fossil plants that are distributed over the

neighboring continents. It is also believed that when the continents are joined together they form a continuous and whole hemisphere. Convection currents are thought to have caused the spreading of materials on the continents due to plate movement.

Continental drift is the relative movement of the Earth’s continents making them to appear as drift on the oceanic bed (Le Pichon et al, 2013). This idea is subsumed by the plate tectonic theory explaining the ways in which the continents move. Separate continents have similarities which suggest that the rocks in them are formed in the same way which imply that they were once joined together. The separation was caused by tectonic movement and convectional currents caused spread of the materials.

Conclusion

Plate tectonic movement generally gives a clear idea of how different plate came to exist. The study of plate tectonic movement gives an account of the existence of the different continents and the distribution of the materials in the respective continents. It gives reasons as to why some continents have similar materials such as rocks and plants. The shape of the earth is also accounted for due to the study of different forces which results to the shaping of the continents and distribution of materials on them. The type’s continental boundaries are clearly expounded with clear list of forces that lead to their existence. The theories related to the plate tectonics are examined and summarized to account for the existence of the continents and the materials on them.

References

• Einsele, G. (2013). Sedimentary basins: evolution, facies, and sediment budget. Springer Science & Business Media.
• Kuzmin, M. I., &Yarmolyuk, V. V. (2016, August).Changes in the manner of tectonic movements
  

under the Earth’s evolution.In Doklady Earth Sciences (Vol. 469, No. 2, pp. 802-806). Pleiades Publishing.