Triple junction

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In East Africa, the East African Rift , the Red Sea and the Gulf of Aden meet as a triple point

As a triple junction (dt .: triple point of batteries also Drilling structure or three-folding structure ) referred to in the geology a point where the borders of three tectonic plates meet.

In plate tectonics, a distinction is made between divergent plate boundaries, where the plates diverge, and convergent plate boundaries, where the plates collide. In addition, there are conservative plate boundaries at which the lithospheric plates slide horizontally past each other. The combinations of the types of plate boundaries at the triple junctions are correspondingly diverse.

Depending on the character of the plate boundaries that meet, triple junctions are specified with a combination of three letters, e.g. B. RRR triple point, TTT triple point or RTF triple point. R (from English ridge ) is a divergent plate boundary, T (of English. Trench ) to a converging plate boundary, and F (of Engl. Trans form-fault ) for a conservative plate boundary.

Mid- ocean ridges (MOR) form at divergent plate edges . Rift fractures run along these ridges and thresholds , where new earth crust is formed by volcanic activity . The concept of triple junction was originally developed using three such drifting plates by W. Jason Morgan , Dan McKenzie and Tanya Atwater . Driven by convection currents , hot mantle material rises and separates the lithospheric plates from one another. If three mid-ocean ridges start from a triple junction ( ridge-ridge-ridge type ), ideally they have equal angles of 120 ° to each other. Such a constellation is shown e.g. B. at the Galapagos Triple Junction , where three oceanic plates, the Pacific plate , the coconut plate and the Nazca plate , drift apart.

If a continental plate breaks apart, a triple junction is also formed initially, but a branch of this junction does not develop any further and ends in an aulacogen . The ocean floor that separates the two new continents finally forms in the other two rift breaks. The opening of the Atlantic Ocean between South America and Africa began with a triple junction in what is now the Gulf of Guinea . The rift valley, which did not develop any further, now forms the Niger Delta and continues along the partly extinct volcanoes in Cameroon (→ Cameroon line ).

In the Afar Triangle in East Africa , too , three rift fractures collide. One branch forms the Red Sea today , a second runs northeast to the Gulf of Aden , both separating the Arabian Plate from the African Plate . The third branch forms the East African Trench , which however no longer develops as quickly and can end in an aulacogen .

literature

  • Naomi Oreskes (Ed.): Plate Tectonics: an Insider's History of the Modern Theory of the Earth. Westview Press, 2003, ISBN 0-8133-4132-9
  • Heinrich Bahlburg, Christoph Breitkreuz: Fundamentals of geology. 2nd Edition. Spectrum Academic Publishing House, Elsevier GmbH, Munich 2004, ISBN 3-8274-1394-X