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Plate Tectonics

 

To better understand the regional geological setting of Cyprus, and indeed the formation of Cyprus itself, one has to be familiarised with the major principles of Plate Tectonics.  According to the theory of Plate Tectonics, the surface of the Earth is not made out of a single continuous crust but rather it is divided into a small number of rigid pieces, the so-called Lithospheric Plates (Fig. 1).  The major lithospheric plates of the Earth are the American, the Eurasian, the Australian, the Pacific, the Antarctic and the Indian (Fig. 2).  These plates are in constant motion relative to each other and form the following three main boundary types (Fig. 3): (a) Divergent boundary, along which the plates are moving away from each other and in the space between them new ocean crust is formed.  There is volcanic and seismic activity along this type of boundary, with extrusion of lava along the spreading axis and weak to moderate earthquakes.  An example of divergent plate boundary is the so-called mid-Atlantic Ridge, where the African Plate moves away from the American Plate; (b) Convergent boundary, along which the two plates collide and one plate moves underneath the other (subduction).  The volcanic and seismic activity in this type of plate boundary is quite significant.  An example of convergent plate boundary is the Hellenic Arc and its continuation towards Cyprus, where the African Plate collides with the Eurasian Plate; (c) Transform boundary, along which the two plates move parallel to each other but in an opposite direction (the plates slide past each other).  No volcanic activity is observed along the transform boundary (also known as transform fault zone), however this is an area that produces catastrophic earthquakes.  A well-known example of transform boundary is the San Andreas Fault on the west coast of the USA, which represents the boundary between the Pacific plate to the west and the American plate to the east.  Figure 4 shows the positions of volcanoes and earthquakes on the Earth.

 

Thus, the Earth is a dynamic planet that changes with geological time.  New crust is created along the divergent plate boundaries, where submarine mountains, known as mid-ocean ridges, are formed.  New oceanic crust can also be created above convergent plate boundaries, having an average thickness of 6 km.  Our knowledge of the oceanic crust comes from geophysical surveys, drilling and submarine observations.  However, the best means of studying the oceanic crust is by examining parts of it that have been uplifted (above sea level) and now constitute part of the land.  Such on-land parts of oceanic crust are called Ophiolites and are usually found along convergent plate boundaries.  The Troodos Ophiolite Complex in Cyprus is a good example of old oceanic crust.



 

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