Compressional Tectonics Issues - Essay Example

Name Instructor Course Date Compressional Tectonics There exist both interior and exterior forces within the earth’s crust that influence the formation of the different landforms found on the surface of the earth. The exterior forces include the forces that contribute to the changes in the structures of the earth such as the weathering of rocks, erosional processes and transportation by the different media such as water, and wind and their deposition in various areas of the earth. Internal forces, on the contrary, result from both thermal and gravitational volatility of the earth’s crust. These instabilities result in the mass movements of the earth. The morphological forms of the earth surface are caused by the movement of the earth’s plates within the lithosphere referred to as plate tectonics. The theory of plate tectonics was first articulated by Alfred Wegner, who used the continental drift theory to explain the tectonic movements of the earth. According to this theory, Wegner suggested the existence of an original continent called Pangaea which split to form Laurasia and Gondwana, then to the continents present today. Although this discovery led to controversy, he managed to find valid proofs from studies in climatology, geology, palaeontology, geodesy and biology. Plate tectonics refers to the study of the movements of the lithosphere and its consequences. The earth consists of different layers with different physical properties and composition. These include the core, the mantle and the crust or the lithosphere. The lithosphere is also divided into several pieces of different shapes, and sizes called the plates. The plates that are currently found on earth include; Africa, Antarctica, North America, South America, Australia, Asia and Pacifica. There are also several other minor plates such as the Philippines and the Caribbean plates. These plates are constantly in motion with respect to one another producing space and friction issues between adjacent plates. These plate movements result in the periodic formation of new plate boundaries and the closure of others. The earth’s lithosphere is constantly under pressure from the tectonic forces which have been in existence throughout history. The tectonic forces vary widely over the earth’s crust thus heightening during the geological periods. Although many of the changes in the structure of the earth have occurred over long periods of time, some of them have been rapid. Since the crustal rocks differ in their strength and composition, their response to the tectonic forces differs, hence resulting in different structures. There are three types of tectonic forces depending on the direction in which the forces are applied. These include the tensional tectonic forces that pull the crustal rocks away from each other, compressional tectonic forces that push the crustal rocks towards one another and the shearing tectonic forces that slide the crustal rocks past each other. Compressional Tectonics Compressional tectonics occur when the tectonic forces operating within the earth’s crust push two areas of the crustal rocks towards one another. This commonly results in the shortening and thickening of the crust. The response of the crustal rocks to the compressional forces depends on the composition of the rocks, which determines their ability to break, as well as the speed with which the forces are applied. As a result, the compressional forces can either result in folding or faulting depending on the amount and the speed of the tectonic forces applied thus resulting in the formation of different structures (Condie, 2015, p. 81). When compressional forces are applied slowly to a rock mass within the earth’s crust, folding occurs. Folding refers to the winding of rock layers and occurs when the compressional forces are applied to rocks that can easily bend rather than those that are easily breakable. The rocks that are deeply seated within the earth’s crust have a higher potential of being distorted without breaking. This is because of the high pressure within the deep regions of the crust that makes the rocks behave like plastic. When folding occurs on any given rock mass as a result of the compressional forces, the upfolds are known as the anticlines while the downfolds are called the synclines. The rock layers forming the margins between the crests and the troughs are known as the fold limbs (Kearey et al., 2013, p. 90) Depending on the amount and speed of the tectonic forces applied and the nature of the subjected rock, folds can vary in sizes ranging from very few centimetres to many kilometres. Folds can also be tight or broad, symmetrical or asymmetrical. Symmetrical folds are formed when the compressional forces acting from the different sides of a rock mass are of equal strength and speed, thus resulting in each limb having the same angle of inclination. In a case where the compressional forces acting from the different sides of a rock are of different strength, the result is the formation of a fold with one limb steeper than the other, indicating different angles of inclination. Such kind of a fold is called asymmetrical fold. Further compression of the asymmetrical rocks may cause them to be overturned, thus resulting in the formation of recumbent folds. An example of a physical feature that indicates the action of the compressional tectonic forces is the Appalachian Mountains. The Appalachian mountain system exhibits the large scale occurrence of folding. Also other examples of folded mountains include; the Rocky Mountains of Colorado, Montana and the Canadian Rockies. The Alps Mountains is also another spectacular example of folding caused by compressional tectonic forces. In the Alps Mountains, the folds are inverted, cut off and mounted on one another. Apart from acting on the rocks that are deeply seated within the earth’s crust, compressional tectonics also acts on the crustal rocks that are near the surface of the earth. The crustal rocks near the surface of the earth are under low pressure and thus are not ductile enough to form folds when subjected to the compressional tectonic forces. Instead, when subjected to the compressional forces, such rocks break and begin to move relative to each other along the fracture created. This process by which crustal rocks near the earth’s surface brittle when subjected to the compressional forces is called faulting. Faulting refers to the process through which rocks are dislodged along fracture surfaces called faults. When compressional tectonic forces cause faulting of rock masses, one side of the rock mass is pushed up at a steep angle in relation to the other or one mass of rock slides downwards on a shallow angle relative to the other. This action of the compressional forces on such brittle rocks result in the formation of fault lines along which the fractured rocks move in relation to one another. In instances where the compressional forces result in the high-angle fractures, the resulting faults are called the reverse faults. (Edward et al, 2014, p. 114) Additionally, where the compressional forces result in low angle faults that supersede the rocks on the other side of the fault, the fracture surface is known as the thrust fault while the dislodgement is called the thrust fault. Thrust faults are the faults formed by compressional forces that have low dip angles. In many cases, thrust faults are unrecognized because of their dislodgement is difficult to detect especially when they occur within the same rocks. Overthrust faults are formed when the angle of inclination of the rock mass within which the compressional forces act is low, usually below 20 degrees and the displacement of the overlying rocks is large, usually in the range of kilometres. There are also different types of the thrust faults formed as a result of compressional tectonics such as thrust duplex and blind thrust faults. When compressional forces cause the faulting of a rock mass, one mass of the crustal rocks is pushed up in relation to the other, this occurs in both the reverse and the thrust faults. In Geography, the direction of movement along the faults in given in relative terms because it is difficult to determine the movement of the rocks that occur during the process with certainty. Overthrust faults, for instance, are found along the Rocky Mountains as well as in the Southern Appalachian. With regards to the above discussion, compressional tectonics is one of the processes through which some of the features on the earth surface such as Fold Mountains are formed. The compressional tectonic forces also act differently on the different masses of rock within the lithosphere depending on the rock structure and the strength of the forces. Of significance is the understanding that the different forces acting within the earth’s crust result in the different features that can be observed on the earth’s surface. Works Cited Condie, Kent C. Plate Tectonics & Crustal Evolution, 2015, p. 81 Edward, Tarbuck, Dennis Tassa and Fredrick Lutgens. Earth: An Introduction to Physical Geology, 2015, p. 114. Kearey, Philip, Keith A. Klepeis, and Frederick J. Vine. Global Tectonics. New York, NY: John Wiley & Sons, 2013, p. 90. Read More