WHAT IS THE CONVERGENT MOTION OF PLATES? - GEOGRAPHY - 2025

The convergent movement of plates or convergent edge is the name assigned to the collision phenomenon between two or more tectonic plates or lithosphere fragments whose life cycle is close to the end. This collision can occur between oceanic and continental plates, always leading to the phenomenon of subduction.

The subduction process is defined as the sinking of one tectonic plate below another. This plate can be oceanic or continental, and inevitably its sinking will give off seismic and volcanic activity.

On the other hand, when subduction takes place, it gives way to the creation of mountain ranges and modifications in the topography of the Earth.

Convergent plate motion happens when two tectonic plates move closer together and collide. Thanks to this impact, the edges of the plates rise and give way to the creation of a jagged mountain range.

Sometimes this impact can also generate channels on the ocean floor. Also, it is common to see volcano chains form parallel to the converging edge.

In the event that one of the continental plates collides with an oceanic plate, it will be forced to sink into the Earth's mantle, where it will begin to melt. In this way, the magma in the mantle will rise and solidify, giving way to the creation of a new plate.

Convergent oceanic and continental border

When an oceanic plate and a continental one collide, the oceanic plate (thinner and denser) will be sunk by the continental plate (thicker and less dense). The continental plate is forced to integrate with the mantle in a process known as subduction.

As the oceanic plate descends, it is forced to pass through environments with higher temperatures.

At a depth of approximately 100 miles, the materials in the subducted plate begin to reach their melting temperature. At this time, the entire plate is said to have entered the molten state.

Magmatic chambers

This process of partial fusion gives way to the creation of magmatic chambers located above the subduced oceanic plate.

These magmatic chambers are less dense than the materials of the surrounding mantle, therefore they float. Floating magmatic chambers begin a slow process of ascent through the upper layers of material, melting and fracturing these layers as they rise.

The size and depth of magmatic chambers can be determined by mapping the seismic activity around them.

If a magma chamber rises to the earth's surface without solidifying, the magma will be expelled over the crust in the form of a volcanic eruption.

Consequences

Some consequences of the convergent edge between a continental and an oceanic plate include: a zone of shallow seismic activity along the continental plate.

However, this seismic activity can be strongest below the continental plate, generating an oceanic trench on the edge of the plate, a line of volcanic eruptions a few kilometers inland from the continental edge, and the destruction of the oceanic lithosphere.

Examples

Some examples of this type of converging edge can be seen on the Washington - Oregon coastline in the United States.

At this location, the Juan de Fuca oceanic plate is being subducted below the North American continental plate. The Cascade Range is a line of volcanoes on top of the subduced oceanic plate.

The Andes mountain range in South America is another example of a convergent edge between an oceanic and a continental plate. Here, the Nazca plate is being subducted underneath the South American plate.

Converging ocean edge

When a convergent edge occurs between two oceanic plates, one of these plates is subducted under the other. Typically, the newer plate will be subducted due to its lower density.

The subduced plate heats up as it is forced into the mantle. At a depth of about 150 kilometers, this plate begins to melt.

The magmatic chambers here are produced as a result of the melting of the subduced oceanic plate. Magma in this case has a lower density than the rocky material that surrounds it.

For this reason, this magma begins to rise, melting and fracturing the layers of rocky material that are found on its way to the earth's surface.

The chambers that reach the surface appear as conical volcanic eruptions. At the beginning of the convergence process, the cones will be submerged in the depths of the ocean, however, later they will grow until they exceed the ocean level.

When this happens, chains of islands are formed that will grow as the convergent movement takes place.

Consequences

Some consequences of this type of convergent edge include: a progressively deeper zone of seismic activity, the formation of an oceanic trench, and a chain of volcanic islands. The oceanic lithosphere is also destroyed.

Examples

Some examples of this type of convergent edge are the islands of Japan, the Aleutian Islands and the islands located on the eastern side of the Caribbean Sea (Martinique, Saint Lucia, Saint Vincent and the Grenadines).

Continental convergent edge

The continental convergent edge is the most difficult to illustrate, due to the complexity involved in this process.

During this process a strong collision takes place, where the two thick continental plates collide. In this case, both have a much lower density than that of the mantle, therefore, neither plate is subducted.

In this way, small fragments of crust and sediment are captured in the middle of the collision of the plates, giving way to the formation of a mixture of rocks without shape.

This compression of materials also causes the folding and breaking of the rocks contained in the plates. These deformations can extend for hundreds of kilometers into the plates.

Consequences

The consequences of the convergent continental edge include: the intense folding and breaking of the continental plates and the creation of highly irregular mountain systems.

On the other hand, surface seismic activity and the thinning or thickening of the continental plates take place near the collision zone.

Examples

The Himalayan system is an example of a convergent continental edge that is in motion today. The Appalachians are an ancient example of this type of converging edge.

References

1. King, H. (2017). com. Obtained from Convergent Plate Boundaries: geology.com
2. Levin, HL (2010). The Earth Through Time. Danvers: Wiley.
3. Mitchell, B. (April 2, 2017). co. Obtained from All About Convergent Plate Boundaries: thoughtco.com
4. (February 14, 2013). Ocean Explorer. Retrieved from There are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries.: oceanexplorer.noaa.gov
5. Wood, D. (2017). com. Retrieved from Convergent Boundary: Definition, Facts & Examples: study.com.