Plate tectonics, a theory that is part of the geological sciences , allows us to explain a vast variety of natural phenomena that occur on planet Earth. The theory is based, in very general terms, in that the lithosphere or lithosphere is fragmented in what we call tectonic plates, that is, they are the parts that make up the lithosphere.
What are plate tectonics and which are the main ones
In a simple way, we can define tectonic plates as fragments of the lithosphere , that is, fragments of the solid surface layer of the Earth, which can be up to 100 kilometers thick. The tectonic plates are suspended in a viscous layer called the asthenosphere , a layer that allows the movement or lateral displacement of the tectonic plates. The plates are considered rigid, since when moving laterally they interact with each other without deforming, except their edges, which undergo considerable modifications.
Furthermore, the lithosphere is composed of 14 main tectonic plates and 46 secondary tectonic plates . The difference between the main and secondary plates lies in their size, the main ones being the largest. Next we will name the 14 main plates:
- North American plate
- South American plate
- Pacific Plate
- African plate
- Eurasian plate
- Australian plate
- Antarctic plate
- Caribbean plate
- Coconut plate
- Nazca plate
- Philippine plate
- Arabic plate
- Plaque of Scotland
- Juan de Fuca plaque
Types of tectonic plates
Depending on the kind of earth’s crust that forms them, tectonic plates can be:
- Oceanic plates: composed of oceanic crust, which is thin and basic composition with iron and magnesium in greater proportion. In general, it is completely submerged in the water of the oceans.
- Mixed plates: composed mainly of continental crust and to a lesser extent oceanic crust. As the continental crust predominates in its composition, some call them continental plates . Most plate tectonics are of this type.
In turn, tectonic plates can be classified according to the type of limit or edge they present:
- Divergent boundary: tectonic plates separate due to the movement that moves them away. This type of limit occurs in both oceanic and continental plates. As the plates separate, the magma rises and seeps through the fractures, giving rise to the formation of new crust.
- Convergent boundary: Tectonic plates collide head-on, and as a result, one of them sinks below the other. The sinking process is known as subduction. Generally the subduced plate is the densest and once in the mantle, it partially melts and creates magma. On the contrary, when two plates have the same density as, for example, in the collision of two continental plates, the obduction process occurs. In this process, no plate sinks, but rather there is a deformation of the edges of both plates in a vertical direction, being joined by a suture zone.
- Sliding limit: tectonic plates slide in parallel but in opposite directions. Here neither the creation nor fracture of the cortex takes place as in the previous cases. These limits are characterized by strong friction between plates.
Why tectonic plates move
Why the tectonic plates move is not yet known exactly. The truth is that plate tectonics is a modern theory that emerged between 1960 and 1970 and is still in full development. What has been proven is the existence of factors that promote the sliding of the plates.
One of the key factors in the movement of plates is related to temperature , more precisely the geothermal gradient , since it creates conditions conducive to movement: a very viscous lithosphere capable of flowing over an asthenosphere with lower viscosity.
Likewise, the geothermal gradient across the planet is completely heterogeneous and, as a consequence, the crust is made up of materials with different densities . Precisely, from the materials with different densities that make up the crust, gravitational forces are capable of generating the different movements of the tectonic plates.
The movements of the plates have multiple effects, mainly on the edges of the plates and in the areas close to the edges. Let’s see here:
- Rift valleys: these are geological fractures that originate from the separation caused by two plates with divergent boundaries.
- Volcanism: volcanoes can be caused by the magma that rises during the separation caused by plates with divergent limits, as well as by the subduction of plates with convergent limits. To better understand volcanism, a consequence of tectonic movement, you can read about How volcanoes are formed and Types of volcanoes .
- Earthquakes: tremors, earthquakes or earthquakes are produced by the collision of plates with convergent limits and also by friction between plates with sliding limits. If you want to learn more about this topic, here you can read about the Difference between earthquakes, tremors and earthquakes and Earthquake: what it is, how it is produced and types .
- Mountain formations: during the process of obduction of the plates with convergent limits, they collide with each other producing folds and distortions at their edges. As a result of the folds and distortions, mountains and mountain ranges originate.
- Transforming faults: they are observed as geological discontinuities in the terrain or also as highly fractured rocky areas. Failures are produced by friction between plates with sliding limits.