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Plate Tectonics.

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Plate Tectonics The lithosphere, or solid outer skin of the Earth, "floats" on the mantle and is broken up into about 7 large and 20 small "plates." The skin hardens and develops cracks. The movement of these plates on the Earth is called PLATE TECTONICS, and plate tectonics are the first step in creating rocks. The theory of plate tectonics describes the ways in which the Earth's surface is deformed as a result of internal geological processes. The basic idea is that the Earth's crust and uppermost mantle (lithosphere) are relatively cool and rigid and float on a mushy layer beneath them in the upper mantle (the asthenosphere). The lithosphere is broken into about a dozen major pieces (or plates) that are "rafted" about on the Earth's surface by convection currents within the mantle. An individual plate usually contains regions of both continental and oceanic crust. The plates interact with one another along their edges, so most geological activity (earthquakes, volcanoes, young mountain ranges, and ocean trenches) occurs along the plate boundaries. The interiors of plates (far from their edges) are usually geologically quiet. ...read more.


Two Oceanic Plates - When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity. Two Continental Plates - When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards. Lateral Slipping Plate Movement: When two plates move sideways against each other, there is a tremendous amount of friction which makes the movement jerky. The plates slip, then stick as the friction and pressure build up to incredible levels. When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake. As a result of plate tectonics, minerals and rocks are formed. The process involved is called THE ROCK CYCLE. The forces at the plate boundaries also contribute. Plate geography The surface of the earth is covered by 7 major plates and several smaller subplates. They move continuously but at different rates. Boundaries, however, are not fixed; plates spread apart and plates weld together. ...read more.


Ridge push Young, 'warm' rock generated at the mid-oceanic ridges is less dense and sits higher in the asthenosphere than older, 'cooler' rock. Gravity makes the lithosphere slip off the elevated ridge. Trench suction Steeply sinking plates will suck the adjacent plate towards the trench. * Tectonic Plates Plates The Earth's crust is made up of seven principal tectonic plates and numerous other smaller plates. The plates are sections of the crust that "float" on the mantle, which is made up of molten rock. Where the plate's meet, huge forces mean that they can form features such as volcanoes, fold mountains, deep-sea trenches and earthquakes. There are two main types of tectonic plate. Oceanic crust is often only about 5km thick, but is very dense. Continental crust is considerably thicker, often being approximately 30km deep, but is less dense. Convection Currents The Earth's Tectonic Plates all move very slowly on the mantle, meeting along the four main boundaries that can be found in the next section. The plates move due to convection currents in the mantle. These are hot currents of molten rock that slowly move within the mantle and cause the plates above Geology and seismic waves project by Izi and Han 10f ...read more.

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