Continental margin
The continental margin is the transition from a continent to the oceanic area. The continental margins are of particular importance for stratigraphy because sediments have been deposited on them or immediately in front of them in the course of the earth's history , which for the most part make up our present-day succession of sedimentary rocks . Of course, this also applies to current geological events.
Division of continental margins
The continental margins are divided into a shallow sea area up to 200 m deep, the continental shelf , the waste to the ocean floor, the continental slope and the foot region of the continental slope with the transition to the deep sea basin on average 4,000 m . A little less than a third of the ocean surface consists of continental margins.
Types of continental margins
According to the geological structure and the role that the continental margin plays in the events of plate tectonics , a distinction is made between active and passive continental margins.
Passive continental margins are characterized by the fact that they do not directly adjoin a continental plate boundary and that no active plate tectonic processes take place at them. They are mainly characterized by expansion, trenching and deposition of sediments. They form a shelf area that can be several hundred kilometers wide and several thousand kilometers long. Mighty series of rocks can form on the shelf area, which, depending on the climatic area, can also be designed as reef belts, such as the Great Barrier Reef off the east coast of Australia . Further examples of passive continental margins include the east coasts of North and South America , the Atlantic coast of Europe and Africa and, in addition to the east coast, also the south and west coast of Australia.
Under Active continental margins pure ocean-continent are generally understood collisions which directly plate tectonic boundaries, primarily at deep-sea trenches over subduction zones , subordinated also on a transform fault lie on the coast of the continent collision usually results in the formation of a mountain, as for example the Andes. Active continental margins of the ocean-continent collision type are characterized by narrow to absent shelf regions and a steep drop into a deep sea channel just a few tens of kilometers off the coast. The coast is often accompanied by volcanic mountain ranges. Examples of active continental margins include the west coasts of North and South America and the east coast of Asia , all of which are part of the Pacific Ring of Fire .
Continental margins in the broader sense also include collisions between two oceanic plates, when they collide, an above-ground island arc is created next to a subduction zone that extends deep into the earth's mantle . Likewise, the term continental margin in the broader sense can describe a continent-continent collision which is usually caused by a thrust and a mountain z. B. Alps or Himalayas is characterized, geologically speaking, a continent-continent collision is often preceded by an active continental margin.
literature
- Rudolf Hohl (ed.): The history of the development of the earth. 6th edition, (reprint of the 5th, revised edition). Werner Dausien, Hanau 1985, ISBN 3-7684-6526-8 .