How do subduction and expansion of the sea floor differ?

Wilson cycle information sheet

Wilson cycle (Klett)

Description of the sequence of plate tectonic processes according to J. T. Wilson.

introduction

The theory of plate tectonics describes the causes and course of tectonic processes (e.g. subduction or collision) on earth. The Canadian geoscientist J. T. Wilson put these tectonic processes in a cycle. The resulting Wilson cycle describes a certain sequence of plate tectonic processes that lead to the cyclical expansion and narrowing of oceans. A cycle is divided into seven phases and lasts around 200-250 million years. The phases are named after typical examples on earth in which the respective stage can currently be found. The theory of the Wilson cycle is very complex - in reality one often finds deviations from the model.

1st phase (resting stage)

At the beginning of the development one looks at a continental plate at rest, for example the Eurasian plate.

2nd phase (digging stage)

If magma rises below the continental plate, the plate bulges. The pressure and tension increase until the continental plate tears along the bulge and a rift develops. Typical examples of this stage are the East African rift system and the Upper Rhine Rift. The rift valley can be accompanied by volcanism (e.g. Eifel).

3rd phase (Red Sea stage)

In the further course, the rise of magma leads to expansion, expansion and subsidence of the trench. The inflowing lava forms a heavy basaltic crust between the two parts of the formerly contiguous continental plate. The further lowering of the trench floor eventually leads to flooding by adjacent seas. This stage can be found e.g. B. in the Red Sea.

4th phase (Atlantic stage)

The continents are moving further apart. Magma still rises on the sea floor and forms new ocean floor through sea floor spreading. In addition, mid-ocean ridges are formed, which are accompanied by volcanism. The sea expands to the ocean. This is in the state of opening (expansion). There is no ore formation at the ocean margins.

5th phase (Pacific stage)

If the drift direction of the continents is reversed, subduction begins at the edge of the ocean. The oceanic plate is submerged under the continental plate, which it has been pushing in front of it up to now. The ocean expansion comes to a standstill and is reversed into ocean narrowing. In the area of ​​subduction one can find volcanoes and deep sea gullies. This 5th phase of the Wilson cycle is z. B. observed in the Pacific Ocean.

6th phase (Mediterranean stage)

As the opposite continents get closer together, the ocean is shrinking and a shallow sea basin is formed. At the continental margins there can be folds and mountainous formation. A typical example of this stage is the Mediterranean.

7th phase (Himalaya stage)

Due to the progressive subduction of the entire oceanic plate at the sea edge, the continental plates finally come together and the gap is closed. The continents collide, fold and push themselves up at the edges to form mighty mountains. The former gap is still visible as a "scar" (mountain). At this stage is z. B. the Himalayas, where uplifts can still be detected today.

8th phase (resting phase)

The erosion of the fold mountains creates a uniform continental plate in the resting state (= 1st phase). The Eurasian plate is at this stage. The Ural Mountains form the border between the former European and Asian plates.

The continental plate of the 8th phase can again be the starting point for a new cycle, which closes the cycle. At the moment there is not just one cycle going on on our earth, but many cycles in many places. These are each in different stages.

References:
Source: Geography Information Center
Author: Sabine Seidel
Publisher: Klett
Location: Leipzig
Source date: 2003
Page: www.klett.de
Processing date: 05/28/2012


Keywords:
plate tectonics


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