History
The history behind Plate Tectonics go back 225 million years ago. All of the continents were all joined together and was known as Pangaea which is one large super-continent. The super-continent was believed to have consisted of two main parts: Laurasia (Asia, Europe, Greenland and North America) and Gondwana (Australia, Antarctica, Africa, India and South America).
180-200 years ago, Pangaea began to break u. Each part of the original land mass (today's continents) slowly drifted to its present location. The broken pieces of the super-continent could all fit back together like the pieces of a giant jigsaw puzzle. This link will show you how the Gondwana was broken up into different continents over the years.
Plate Boundaries
At the boundaries they diverge, converge or slide past one another. Each type of boundary produces distinctive and recognisable land-form features.
Diverging Boundaries
Diverging boundaries are the points where plates separate and new crust is created. As the plates move apart, molten material fills the gap, forming a mid-ocean ridge. These ridges extend for some 65000 km throughout the earth's oceans. The islands of Hawaii in the mid-Pacific are, for example, the peaks of a mid-ocean ridge.
Converging Boundaries
Converging plate boundaries are the points where plates collide. The process of sea-floor spreading increases the earth's land surface area.The destruction of the old lithosphere takes place in the subduction zones. A subduction is an area where two tectonic plates come together, one riding over the other. The following are the types of collisions that occur:
- Colliding oceanic and continental plates. When an oceanic and a continental plate collide, the dense floor of the ocean is subducted (or forced down) beneath the less dense continental plate. This forms a deep trench. The descending slab of the sea floor melts and then erupts in a chain of volcanoes along the edge of the continental plate. The Andes Mountains of South America were formed this way over hundreds of millions of years.
- Colliding oceanic plates. When oceanic plates collide, the plate that is older, colder and therefore denser, subducts under the other, forming a trench. This movement weakens the crust and molten rock escapes to the surface, forming islands of volcanic mountains. Chains of active volcanoes form on the landward side, parallel to the deep sea trench. Examples of such island arcs in the Pacific basin include the Aleutians, the Philippines and Japan.
- Colliding continental plates. When two continental plates collide, neither will subduct because both are of the same density. Volcanism is not common in these areas, but folding of the crust, mountain-building and earthquakes occur over a broad area. The Himalayan Mountains were formed in such a way and are still moving. After the breakup of Gondwana, India moved as an island some 3000 km from its original location in the Southern Hemisphere. The continents eventually collided, with India pushing deep into Asia.
Horizontal Movement
Where plates move horizontally past each other along a single vertical fault line, the release of built-up pressure causes earthquakes. The San Andreas Fault in California is a major fault system arising from movement between the pacific and North American plates.
Map of Global Plate Boundaries
The map below shows the plate boundaries all around the world.