Tectonic Plates (3)-Plates and Plate Margins
Oceanic Crust; Newer-most less than 200 million years old, denser, can sink, thinner, can be renewed and destroyed. Continental Crust; Olider-most over 1500 million years old, less dense, thicker, cannot sink, cannot be renewed or destroyed.
Key terms; -Subduction- The sinking of oceanic crust at a destructive plate margin.
-Collision- The meeting of two plates of continental crust. They are both the same type so they meet 'head on' and buckle.
Destructive Margins; Destructive margins are where two plates are moving towards each other. Convection currents in the mantle cause the plates to move together. If one plate is made from oceanic crust and the other from continental crust, the denser oceanic crust sinks under the lighter continental crust in a process known as subduction.The oceanic plate is forced down into the mantle. Great pressure is exerted and the oceanic crust is destroyed as it melts to form magma. This often forms volcanoes and ocean trenches (very deep sections of the ocean floor where the oceanic plate goes down). If two continental plates meet each other, they collide rather than one sinking beneath the other, no crust is destroyed. This collision boundary is a different type of destructive margin.