make an assignment on "plate tectonic theory" explain with details
Answers
Answer:
Definition
Plate tectonics is a theory that the Earth’s lithosphere (the crust and upper mantle) is divided into a number of large, platelike sections that move as distinct masses. The movement of the plates is believed to result from the presence of large convection cells in the Earth’s mantle which allows the rigid plates to move over the relatively plastic asthenosphere. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s.
By definition the word “plate” in geologic terms means a large slab of solid rock. “Tectonics” is a part of the Greek root for “to build” and together the terms define how the Earth’s surface is built up of moving plates. The theory of plate tectonics itself says that the Earth’s lithosphere is made up individual plates that are broken down into over a dozen large and small pieces of solid rock.
Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere, each topped by its own kind of crust. Along convergent boundaries, subduction, or one plate moving under another, carries the lower one down into the mantle; the material lost is roughly balanced by the formation of new (oceanic) crust along divergent margins by seafloor spreading.
History of Plate Tectonics
The concept of plate tectonics was formulated in the 1960s. According to the theory, Earth has a rigid outer layer, known as the lithosphere, which is typically about 100 km (60 miles) thick and overlies a plastic layer called the asthenosphere. The lithosphere is broken up into about a dozen large plates and several small ones. These plates move relative to each other, typically at rates of 5 to 10 cm (2 to 4 inches) per year, and interact along their boundaries, where they converge, diverge, or slip past one another.
Plate tectonics is the unifying theory of geology, said Nicholas van der Elst, a seismologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York.
“Before plate tectonics, people had to come up with explanations of the geologic features in their region that were unique to that particular region,” Van der Elst said. “Plate tectonics unified all these descriptions and said that you should be able to describe all geologic features as though driven by the relative motion of these tectonic plates.”
There are seven major tectonic plates (North America, South America, Eurasia, Africa, Indo-Australian, Pacific and Antarctica) as well as many smaller, microplates such as the Juan de Fuca plate near the United States’ state of Washington (map of plates).
The key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates, which ride on the fluid-like (visco-elastic solid) asthenosphere. Plate motions range up to a typical 10–40 mm/year (Mid-Atlantic Ridge; about as fast as fingernails grow), to about 160 mm/year (Nazca Plate; about as fast as hair grows).
Some important topics on Plate tectonics :
Plate boundaries – The lithospheric plates are much thicker than the crusts of the oceans or continents. Hence, their boundaries do not merge with that of the oceans and continents, and their behavior is someway different from that of oceans and continents.
Divergent margins – As plates separate from each other, or diverges, the release of pressure causes melting of the primary layer. This molten material, which is called magma, is basaltic in nature and buoyant in nature. As a result, it gushes forth and cools close to the surface to create new crust.
Convergent Margins – The formation of Earth’s new crust produces an additional crust that needs to be balanced by the destruction of one or more crusts elsewhere. This is accomplished at the convergent plate boundaries, where one plate descends making an angle with the another one.
Continental rifting – This is a process by which the continental lithosphere extends in volume. It is the belt or zone of the continental lithosphere, where the extensional deformation or rifting is taking place. These sectors have high significance and geological structures, and if the rifting is successful, new ocean basins are formed.
Mantle Convection – Tectonics forces are the result of mantle convection. Mantle convection appears due to thermal expansion of mantle material upon heating, which causes a drop in the density in comparison to the overlying fluid. The resulting buoyant forces cause the material to move upwards. Once it reaches the surface, it cools down and becomes denser. As its density increases to a certain extent, it sinks below. As the process continues, it is called mantle convection.
Besides, there are many other important topics, like rift basins, ocean basins, earthquakes, volcanism, seafloor spreading and many more.
NOTE: And stick shift some pictures about plate tectonics.
The heat and pressure from the Earth's molten magma causes convection currents. This generate forces that causes movement of the plates. This theory is known as plate tectonic.
I THINK THIS WILL HELP YOU
Follow me