Plate Tectonics Essay

Plate Tectonics

Plate tectonics is a principal process that largely forms the face of the Earth. It divides over ninety percent of the Earth surface into fifteen primary pieces of lithosphere known as tectonic plates. Plate tectonics is a recognized modern geological theory addressing the motion of the lithosphere. According to this theory, tectonic plates are giant pieces of lithosphere, which altogether provide the planet with a mosaic structure. Slow motions of tectonic plates subsequently result in the movement of both the ocean floor and continents. Plates encounter with each other, extruding the solid earth to form ridges and mountain ranges or denting it to create deep basins in the ocean. Their activity is mainly interrupted by short catastrophic events like earthquakes and volcanic eruptions. Primary geological activity is concentrated along the plate boundaries. The fact that the plates are moving has been scientifically proved with the help of satellites, which can accurately measure changes in distance between two points on different plates and determine the speed of their movement. Nevertheless, the mechanism of the movement of tectonic plates is currently under study. The existing theory explains movement of plates by pressure originated in the mantle. Unfortunately, the theory of plate tectonics does not provide an accurate explanation of how the movement of plates is related to processes taking place in the depths of the planet. Joint efforts of geologists, geophysicists, physicists, chemists, mathematicians, and geographers working in the National Park Service have resulted into an efficient technical and scientific description of the structure and movement of lithospheric plates.

Location of Tectonic Plates

Being a significant geologic construct, plate tectonics provides accurate data referring to location of lithosphere plates. The analyzed phenomenon is theoretically based on the fact that the exterior layer of Earth, also known as the lithosphere, is divided into solid pieces called tectonic plates. The forenamed fifteen tectonic plates are named in accordance with their location: the African plate, the North American plate, the Arabian plate, the Cocos plate, and the Nazca plate, along with the Caribbean plate, the Eurasian plate, the South American plate, the Philippine sea plate, the Juan de Fuca plate, the Australian plate, the Antarctic plate, the Indian plate, and the Pacific plate (Saunders, 2011). The mentioned plates occupy around ninety percent of the Earth’s rigid surface.

Figure. 1. Tectonic plates of the Earth (Lillie, 2005).

Tectonic plates like the Eurasian plate and the North American plate mainly consist of continents, while tectonic plates such as the Antarctic plate and the Pacific plate are primarily located under the world ocean. The first group of plates shapes the continental crust of Earth, while the second group participates in the formation of the ocean crust of the planet. The planet’s continents are continuously moving due to motions of the listed tectonic plates. Each of the aforementioned plate moves with an individual speed up to ten centimeters per year and in a specific direction in relation to other plates. Consequently, the plates may crush, pull apart, and sideswipe each other. Location of the place of contact of two tectonic plates is knows as a plate boundary (Oskin, 2013). Names of boundaries depend on moving patterns of the plates as opposed to each other. Correspondingly, it is vital to note that initial location of the plate changes annually, creating new geological boundaries around the planet.

Physiographic Characteristics of Tectonic Plates

It is important to mention the fact that only eight out of the general amount of tectonic plate are defined as the most stable areas of the Earth’s surface. The following plates are considered to be stable due to the performed moderate velocity: the Antarctic plate, the Australian plate, the African plate, the Eurasian plate, the Indian plate, the Pacific plate, the South American plate, and the North American plate (Saunders, 2011).

Australia and its surrounding part of the ocean, reaching Hindustan, represent the Australian plate. The currently observed movement of the given lithospheric plate is directed from the east at a speed of approximately 67 millimeters per year (Frisch, Meschede, & Blakey, 2010, p.11);

The Antarctic plate occupies the lower part of the planet with Antarctica and adjacent portions of the oceanic crust. This plate is relatively stable as it is surrounded by mid-ocean ridges and other lithospheric plates are moving away from it (Frisch, Meschede, & Blakey, 2010, p.5);

The African continent along with the section of oceanic crust, which occupies a part of the bottom of the Indian and Atlantic oceans, constitutes the African plate. The northern part of the plate has experienced a vast breakage, separating Arabian Peninsula from the African continent. Neighboring tectonic plates tend to move away from the African plate while the plate itself produces motions leading to its sinking into the Earth’s mantle with the velocity of approximately twenty-seven millimeters per year. In other words, the plate is experiencing the phenomenon known as geologic subduction (Frisch, Meschede, & Blakey, 2010, p.15);.

The Eurasian plate is shaped by the main part of the Eurasian continent except Hindustan, the Arabian Peninsula, and the northeastern “corner” of the continent. It is the largest lithospheric plate in the world in terms of the content of continental crust (Frisch, Meschede, & Blakey, 2010, p.11);

The Indian plate allocates Hindustan. It is peculiar for collision with the Eurasian plate, which gave birth to the Tibetan Plateau and the Himalayas. The tectonic plate continues its movement in the northeastern direction at the velocity of fifty millimeters per year, while the Eurasian plate tends to avoid further collisions at the approximate speed of twenty millimeters per year. Additionally, the plate possesses three subduction areas, which precondition its sinking into the mantle. The sinking occurs at the rates of fifty-five, sixty-seven, and eighty-seven millimeters per year correspondingly (Frisch, Meschede, & Blakey, 2010, p.7);

>

The Pacific plate is formed by the site of the oceanic crust, shaping the bottom of the Pacific Ocean. In the area of California, the plate moves northward at a rate of fifty-five millimeters per year. The size of the Pacific plate is steadily declining due to several subduction areas. Under the Eurasian plate, it is sinking into the mantle at a rate of seventy-five millimeters per year. Under the Indian plate, it sinks at a rate of eighty-two millimeters per year. Under the North American plate, it approaches the mantle at a rate of thirty-five millimeters per year, and at a rate of twelve millimeters per year under the medium-sized Philippine lithospheric plate (Frisch, Meschede, & Blakey, 2010, p.16);
The North American plate is shaped by the North American continent, the north-western part of the Atlantic Ocean, about half of the Arctic Ocean, and the northeast “corner” of Eurasia (Frisch, Meschede, & Blakey, 2010, p.13);

The South-American plate constitutes South America and a part of the ocean crust of the Atlantic Ocean. The plate has two subduction zones of nineteen and five millimeters per year (Frisch, Meschede, & Blakey, 2010, p. 2).

Tectonic plates posses several physiographic characteristics, which primarily deal with location of continents and oceans, shaping mountain chains and ocean trenches and leading to the rising activity of earthquakes or volcanoes. The continental crust is ordinarily older and thicker than the oceanic crust of tectonic plates. The first one ranges from thirty-five up to seventy kilometers, while the latter is usually from seven to ten kilometers (Saunders, 2011). Thickness of the crust directly affects its mobility and its physical integrity as the majority of physical formations occur on the planet’s tectonic plates. In terms of psyhiography, there are three main groups of tectonic plates’ boundaries: convergent, divergent, and transform boundaries. The tectonic plates that approach each other create the so-called convergent boundaries (Frisch, Meschede, & Blakey, 2010). Geological theory identifies the plates, which are moving away from each other, as plates creating divergent boundaries and the ones that are sliding by each other have transform boundaries. In addition, modern plate tectonics defines plate rift zones, i.e. territories where boundaries are not clearly defined and that may transform relatively quickly.

Figure 2. Types of plate boundaries (Israel, 2012)

Divergent boundaries are places, which generate a new crust from energy obtained from the plates pulling away from each other. Divergent boundaries are the major precondition of the existence of certain volcanoes, valleys, and trenches all over the globe, for instance, numerous volcanoes in Iceland and deep rift valleys located in eastern Africa (Frisch, Meschede, & Blakey, 2010, p.195). Convergent boundaries, in turn, are defined as places where the crust is destroyed due to the collision of two tectonic plates diving one under another. It is owing to convergent boundaries that the geological society has the opportunity to study ocean trenches and such chains of mountains as the Andes in South America and the Himalayas in India. In addition, convergent boundaries are to take full responsibility for the existence of volcanoes on the planet. According to the theory of plate tectonics, transform boundaries neither bring forth nor break the crust as they slide by each other using a horizontal pattern. These boundaries create the planet’s seismic active locations such as the California region known as the Ring of Fire (Oskin, 2013).

Figure 3. Planet’s earthquake activity map (Lillie, 2005).

Stratigraphy of Tectonic Plates

The National Park geology holds a significant place in terms of the stratigraphy of tectonic plates. Stratigraphic columns for different tectonic locations vary due to the origin of their formation. This is the reason why it is more appropriate to analyze the stratigraphy of tectonic plates using concrete national parks and monuments. The paper analyzes the example of the Bryce Canyon National Park located in Utah and presents the stratigraphic column of its tectonic history (Stratigraphy of Bryce Canyon national park and vicinity, n.d.). The stratigraphic column provides data referring to tectonic history of the North-American plate. As seen on Figure 5, the ground base of the canyon in the majority of its parts is represented by Wahweap formations of the mid to late Cretaceous (100-75 MYA). The latter belongs to the period when the territory of North America was covered by an inland sea dividing the continent into two halves (Anderson, Chidsey, & Sprinkel, 2010). The shore of the forenamed inland sea formed shale and sandstone deposits along its shore. Reptiles, mollusks, and other ammonite fossil assemblages formed the John Henry and Drip Tank constituents of the stratigraphic column (Stratigraphy of Bryce Canyon national park and vicinity, n.d.). Fossil accumulations of the upper part of wahweap formations included mammals, crabs, dinosaurs, and freshwater fish.

Figure 4. The prominent pink cliffs present at the Bryce Canyon (Israel, 2012).

Correspondingly, the latter suggests that rocks of the canyon were formed in the shoreline area of the inland sea. Kalparowits Formation, located above the Wahweap Formation, in Figure 5 is seen to be consisting of alluvial floodplain deposits and shoreline fossil assemblages such as sharks and rays. Bryce Canyon is widely known for its pink, orange, and buff colored rocks. The mentioned colors have their origin in the Claron Formation of the Tertiary period (Anderson, Chidsey, & Sprinkel, 2010). These rocks were deposited after the recession of the inland sea in the alluvial plains, deltas, and river channels.

Figure 5. The stratigraphic column of Bryce Canyon (2014).

Figure 5 exposes formation of pink hollow formation and pink limestone member at the sea level of the inland sea as it contains rocks formed in deltas. The white limestone member, along with the sandstone member was formed in broad lakes after the recession of the inland sea.

The conglomerates of sandstones and mudstones were formed after numerous floods affected the climate change in the Eocene. The next level above the Claron Formation is the Mount Dutton Formation and the Osiris Tuff as results of relatively violent volcanic activity during the period from 40 MYA until 23 MYA. Top layers of the Bryce Canyon are to be analyzed as the result of quiet volcanic eruption forming boat mesa conglomerate, younger basal, and quaternary deposits after 20 MYA (Anderson, Chidsey, & Sprinkel, 2010). Thus, the stratigraphy can be addressed as a vital component of the changing nature of the tectonic activity and the natural observation of tectonic processes producing them.

Petrology of Bryce Canyon

The primary petrology patterns of the Bryce Canyon are associated with the Hoodoos, the pinnacle rocks rich in calcium carbonate. As calcium was historically washed away by water erosion from the rocks, it left horizontal traces (grooves and protrusions), which greatly contributed to the beauty of the national park. The chemical decay is the key to the variety of colors presented within the Bryce Canyon. The mentioned decay resulted from the oxidization of iron presented in the compound of the canyon rocks. Oxidization of iron produced primarily red colored mineral called hematite (Fe2O) constituting the Pink Cliffs. Along with hematite, the area is reach in limonite (FeO(OH), a yellow tint produced by the iron’s reaction with water. In addition, manganese constituents (MnO) evolved into the lavender shades of wall staining (Chronic & Chronic, 2004). Dolomite rocks along with pure limestone form the white color seen on the canyon walls.

According to Figure 6, the petrology of Bryce Canyon national park reveals five primary groups of mineral cliffs: pink, gray, white, vermilion, and chocolate cliffs, which are principal accumulations of the platform sediments (Foos, 2011). The chocolate cliffs are tapeats sandstones created during early Cambrian Period by the ocean waters. The grey cliffs come from the Muav limestone, which was deposited during the late Cambrian Period due to the Sauk Sea transgression.

Figure 6. Cross-section of Bryce Canyon (Foos, 2011).

The petrology of the Bryce Canyon has its roots in the late Cretaceous period and the first half of the Cenozoic era. The Claron Formation formed the hoodoos and the monolith parts were presented by the white cliffs. The hoodoos, in turn, are built from sedimentary rocks and cretaceous rocks, making the Bryce Canyon National Part one of the most interesting places on the planet in terms of mineral formations.

Structure of Bryce Canyon

Bryce Canyon consists from picturesque fourteen amphitheaters, which are located along the edge of the Paunsaugunt Plateau. The sedimentary conglomerate of this national park was formed by erosion of water and exposure to strong winds. Consequently, it evolved in the formation of rock fins and hoodoos. As mentioned before, the Bryce Canyon contains numerous joints and fractures. The joints of the Bryce Canyon are vertical and are ordinarily set in parallel groups. Large-scale crustal movements along with the erosion pressure and removal of overlying sediments have historically generated these parallel groups known as hoodoos (Anderson, Chidsey, & Sprinkel, 2010). Besides the rock structures, which are widely present in Bryce Canyon, there are several specific structures assisting in the identification of the tectonic history of the region. These specific structures are known as faults and are located around the national park due to crust deformation. The canyon’s structure attains both normal and reverse faults, which makes its landscape very attractive in terms of geology. The hoodoos themselves resulted from the uplifting of rocks, which significantly expanded, forming an exfoliation dome (Anderson, Chidsey, & Sprinkel, 2010). As the rock is uplifted and expands, perpendicular fracture planes are created. These fractures are generated by the exfoliation that is eroded to consequently shape peninsular rocks and walls. The latter is eroded to form the canyon’s arches and, with time, it is reduced to hoodoos.

Geologic History of Bryce Canyon

The surface of the Bryce Canyon National Park consists mainly of rocks belonging to the Tertiary, Cretaceous, and Jurassic periods. The Bryce Canyon has been scientifically proved to exist over sixty million years during the Eocene epoch of the Tertiary Period. Sixty million years ago, the territory of the Bryce Canyon was covered with waters of inland seas and lakes. The long-term exposure to water erosion led to two thousand feet deposit of large amount of silt, lime, and sand. As s result of severe storms and changes in weather, it has evolved into a unique geological area (Foos, 2011). The region was shaped by numerous mudslides, volcano eruptions, and water erosions, which moved sediment and stimulated deposition of different minerals in the canyon’s layers. The major result of the changes that occurred in the area was related to the accumulation of sand, gravel, and sedimentary within the basin of the inland sea. With time, the forenamed accumulations hardened and transformed into the compounds of the Claron rock formations of the canyon hoodoo sculptures. The first premises of the canyon formation were preconditioned by extensive interior seaway located in the Western interior basin of North America. The Bryce Canyon geological history comprises two major historical periods: the Mesozoic and the Cenozoic periods. Clearly, the Mesozoic rocks are tapped by Cenozoic rocks because of intense regional erosion.

  • The Mesozoic Period. The Mesozoic rocks, specifically Jurassic age rocks at Bryce Canyon, begin the record of the surface geologic history in the area with limestone, dolomites, sandstones, and shale. As the Jurassic period lasted for more than hundred million years, it provided invasion of shallow seawater to the northeast-southwest border of Utah. The latter margin was pertained to relate to the Andean-type formations, which similarly provoked volcanic activity in the seduction areas. The described process is traced nowadays in the mountain system of the Andes (Foos, 2011).
  • The Cenozoic Period. It is addressed as a more modern period of the canyon development that happened roughly forty million years ago. The forenamed segment was distinguished by the arrangement of the upper levels of hoodoos consisting of the Claron Formation or the Bryce Limestone. The Claron Formation appeared in the result of local basins filled with sediments, creating hoodoos, amphitheatres, and other outstanding geological shapes observed at Bryce Canyon today.

Conclusion

Plate tectonics is a complex theoretical notion in geology due to its ability to clarify and elucidate the geological history of the surface of Earth. Bryce Canyon in Utah is an outstanding example of the insight brought by plate tectonics. According to the theory of plate tectonics, minerals and multiple vertical structures found in the canyon uncover the geological history in terms of what happened in the geologic past of the area. It has been proved that cliffs presented at Bryce Canyon were initially formed at the sea level. This answers the question of the origin of the presently observed mountain plateau formed by sedimentary accumulations. Severe volcanic eruptions experienced in the canyon’s region consequently led to the formation of various faults and specifically volcanic rocks. Evidently, throughout the history, Bryce Canyon has survived much weather- and climate-related stress. Modern convergent plate boundaries present many of the same volcanic rocks and faults. Elevation of the site indicates that tectonic forces uplifted the entire era. The uplift observed at Bryce Canyon is obviously the result of a regional tectonic activity. After it occurred, the area began to erode, creating a valley filled with water from rivers, frost, gravity slides, and winds. The theory of plate tectonics is to be perceived as the driving force of comprehending processes occurring on the planet millions of years ago and processes that are to be expected in the coming centuries.

Sample