Plate Tectonics

Tectonic plate 

• A tectonic plate can also be called a lithospheric plate. It is massive in structure and an irregularly shaped slab of solid rock. Plate tectonics is generally made of both continental and oceanic lithosphere.
• Over the asthenosphere, plates move horizontally as rigid units.
• The lithosphere includes the crust and the mantle. The thickness of the lithosphere varies between 5 and 100 km in oceanic parts and about 200 km in continental areas.
• Depending upon the position of the plate, the plate is called a continental plate or oceanic plate.
• It is divided into seven major and some minor plates based on the theory of plate tectonics.
• The major plates are surrounded by young fold Mountains, ridges, Trenches, and faults.
• Alfred Wegner believed that continents never moved. He thought that the Continent is a part of the plate and the plate is the one that moves.
• The continental masses left in the plates will keep on moving all over the geological period. It was identified in later discoveries.
• Pangaea was a result of the continental drift theory. It was formed from parts of one or the other plates.
• The location of the Indian subcontinent(primarily peninsular India) is traced with the help of rock analysis in the Nagpur area.

Types of Plate Boundaries

Divergent Boundaries

• Plates pull away from each other and lead to the generation of new crust.
• Diverging Boundaries: Spreading sites where the plates move away from each other.

Example of divergent Boundaries

The mid-Atlantic ridges – At these plates, the American Plates are separated from the Eurasian and African Plates.

Convergent Boundaries

• The location or the part where the sinking of the plate occurs is called the subduction zone.
• Convergence can occur in three ways. They are

1. Between an oceanic and continental plate
2. Between two oceanic plates
3. Between two continental Plates

Transform Boundaries

• As the plates slide horizontally to each other, the crust is neither produced nor destroyed.
• Transform faults act as planes of separation and are generally perpendicular to the mid-oceanic ridges.
• The eruption does not take along the entire crust at the same time. So, there is a differential movement of a portion of the plate away from the earth’s axis.
• The rotation of the earth has its consequence on the separated blocks of the plate portions.

Formation of volcanoes

• Melting is prevalent along plate convergent borders.
• The Pacific Ocean basin is bounded by converging plate boundaries, which result in volcanic arcs.
• Pressure release causes melting at divergent plate borders.
• The seabed is pushed apart and new seafloor is formed along mid-ocean ridges.

Rates of the Plate Movement

• To determine the rate of plate movement the strips of the normal and reverse magnetic field that parallel the mid-oceanic ridges are used.
• The rates of plate movement changes considerably.
• The slowest rate of plate movement which is less than 2.5 cm/yr is from the Arctic Ridge.
• The east pacific rises near Easter Island, in the south pacific, has the fastest rate( more than 15 cm/yr)

Force for the Plate Movements

• Many scientists thought the earth was a solid, immovable body. This idea came to scientists as a result of Wegener’s theory of continental drift.
• But the concept is written in the seafloor spreading, and the unified theory of plate tectonics has a significance that both the surface of the earth and the interior are dynamic.
• The moving rocks located beneath the rigid plates are believed to be moving in circular motion.
• The heated material can rise to the surface, spread, and begin to cool. The cool mixture again sinks back into more profound depth. This process is called convection cell or convective flow.

• Heat with the earth comes from two sources

1. Radioactive decay
2. Residual Heat

• Arthur Holmes first considered the plate driving force idea. But it influenced Harry Hess to think about seafloor Spreading.
• The driving force behind the plate movement is the slow movement of the hot and softened mantle that lies below the rigid plates.

Conclusion

Plate tectonics is the theory that the Earth’s lithosphere (the crust and top section of the mantle) is split into about 12 big plates and numerous smaller plates that float on and migrate independently across the asthenosphere. In the 1960s, the theory transformed the geological sciences by merging the previous notion of continental drift with the new concept of seafloor spreading into a cohesive whole. Each plate is made up of hard rock that was formed by upwelling magma along oceanic ridges where plates diverge. A subduction zone arises when two plates collide, forcing one plate beneath the other and into the Earth’s mantle. The bulk of earthquakes and volcanoes on Earth’s surface occur at tectonic plate boundaries. A plate’s interior travels like a hard body, with only slight shifting, few earthquakes, and limited volcanic activity.