Plate Tectonics


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    The Theory of Plate Tectonics suggests that the earth's crust is broken into large pieces called plates. According to the theory, the occurence of earthquakes, mountain building and volcanoes can be explained in terms of the movement of parts of the plates in the earth's crust.
    The Earth's crust may be of two types; the continental crust and the oceanic crust. These differ in thickness and composition.The two types of crust are believed to have formed as the young Earth cooled. Convectional currents in the partially molten magma are believed to drive the movement of the plates across the Earth's surface. 
    Places where the oceanic plate plunges under the continental plate are called subduction zones. Mountain building and volcano formation occurs here.
    Places where plates move apart are called spreading zones. New crust is formed here.
    Volcanoes are also often found in these regions.
    Some volcanoes occur in the middle of a plates, as it passes over a "hot spot" in the mantle.
    Queensland's extinct volcanoes are believed to have formed this way.

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    Pages by Sally Mack 1998-2001