Plate Tectonics: A Comprehensive Guide to Earth’s Dynamic Surface
Plate Tectonics
Introduction
The thermal motion of the Earth’s interior causes significant changes on its surface, explained by the theory of plate tectonics. This theory proposes that the lithosphere, the Earth’s rigid outer layer, is divided into several fragments called tectonic plates. These plates move horizontally past one another, driven by convection currents and subduction. Numerous pieces of evidence support this theory, including the age of oceanic crust, heat flux in ocean basins, and the assemblage of fragments from the supercontinent Pangaea.
Types of Plate Boundaries
There are three main types of boundaries between tectonic plates:
- Constructive Boundaries: These are diverging edges where new lithosphere is created. They occur when two plates separate, allowing magma to rise and solidify, forming new crust.
- Destructive Boundaries: These are convergent zones where lithosphere is destroyed. This happens when one plate subducts, or slides beneath, another plate. This process is called subduction.
- Passive Boundaries: These are boundaries where plates slide horizontally relative to each other along fractures called transform faults.
Evolution of Lithospheric Plates
Lithospheric plates are not static but constantly evolve. This evolution is thought to occur as follows:
- A continent breaks apart, usually due to a hotspot, a plume of hot material rising from the mantle. The hotspot thins the lithosphere, eventually causing it to break, creating a new ocean basin.
- The two continental fragments separate, driven by the injection of molten material from the asthenosphere, the layer beneath the lithosphere. This forms an ocean.
- Pressure from the rising magma, differences in thickness and density between the oceanic and continental lithosphere, causes the oceanic lithosphere to break at the point where it meets the continental lithosphere. The denser oceanic lithosphere subducts beneath the continental lithosphere.
- The two continents, now separated by an ocean, continue to move towards each other. Eventually, they collide and merge, forming a continental suture. This process is known as the Wilson Cycle.
Supercontinents and Their Impact
The movement of plates can force continents to collide and merge, forming a supercontinent. Throughout Earth’s history, such supercontinents have formed repeatedly. These massive landmasses prevent the cooling of the mantle beneath them, leading to a significant accumulation of energy. The collision of continental masses causes the uplift of mountain ranges and can also influence climate and the biosphere.
Consequences of Plate Tectonics
Constructive Boundaries: Mid-Ocean Ridges and Transform Faults
Mid-ocean ridges are underwater mountain ranges that extend across the ocean floor. They are the sites where new oceanic crust is formed. These ridges are about 1,000 km wide and 2,000 meters high.
Transform faults are strike-slip boundaries where plates slide horizontally past each other. These faults are perpendicular to the axis of mid-ocean ridges. Significant stresses occur along these faults, leading to earthquakes. Magmatism can also occur if compression builds up and releases elastic energy.
Destructive Boundaries: Subduction Zones
Subduction occurs when oceanic lithosphere sinks beneath continental crust. This happens due to the cooling and increasing density of the oceanic lithosphere as it moves away from the mid-ocean ridge. As subduction progresses, a trench forms at the junction of the two plates, where sediments accumulate.
Subduction results in several phenomena:
- Seismicity: Friction between the plates causes earthquakes, both due to rifting (pulling apart) and compression.
- Magmatism: The friction and compression of materials generate heat, leading to the formation of magma that rises to the surface, forming volcanoes.
- Metamorphism: Rocks undergo changes in their mineral composition and texture due to the high pressure and low temperature conditions in subduction zones.
These phenomena contribute to the formation of various types of mountains and geological features.
Folds and Faults
Rocks and Earth materials deform and displace due to the movement of the lithosphere. The deformation depends on several factors, including the type of rock and the intensity of the force applied.
Rocks can undergo three types of deformation:
- Elastic Deformation: The rock returns to its original shape after the force is removed. This can create tectonic depressions and faults.
- Plastic Deformation: The rock permanently changes shape without breaking, resulting in folds.
- Fracture: The rock breaks due to the exceeding of its strength, producing faults and joints.
Folds
Folds are distortions resulting from the bending or twisting of rocks. They are produced by the action of force couples in a horizontal plane.
Faults
Faults are fractures in the Earth’s crust where there is relative displacement of the separated parts. They occur when the stress on the rocks exceeds their plastic limit, causing them to break. Faults can occur due to extension (pulling apart) or compression. Normal faults occur in areas undergoing extension, while reverse faults occur in areas undergoing compression.
Intraplate Processes
: lithospheric plates are rigid, but sometimes the inside of the plate is perforated by molten rock coming from the mantle. The oceanic lithosphere has a very rugged topography. All these accidents originate in the asthenosphere, where a large amount of magma reaching the surface through ductwork uan .. These areas of oceanic intraplate volcanism seems ntene originated in hot spot areas. These are areas that are mantle temperature higher than the amount by convection Enteron and hot rocks. When these rocks are close to the lithosphere partial fusion occurs and may reach the surface .. The inland areas suffer more than volcanic tectonic changes, but at some point where thermal laanomalia is important and not so thick crust, volcanic trails can be found within the continent.