Real Science Radio: Plate Tectonics. Not.
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The crust ranges from 5 to 10 km thick in the dense basaltic oceanic crust, and up to 75 km in the thicker, less dense granitic rock of the continental crust. This difference in density and thickness of these two types of crust is the reason why the earth has oceans and continents. The crust is often mistaken for the tectonic plates; however, the crust is just the top part of the tectonic plates. The uppermost brittle mantle behaves much like the overlying crust, and together they form a rigid layer of rock called the lithosphere that moves in unison. The lithosphere ranges from as much as 100 km thick in the oceanic plate to 200 km thick in the continental plates. It is in this brittle zone that earthquakes occur, due to compression, extension, and sheering.
Over billions of years, the cool surface of the earth has been broken up into the moving plates that are called lithospheric plates, or, more commonly, tectonic plates. Because they are mostly more buoyant than the asthenosphere, they float above it. Convection currents driven by temperature, pressure, and gravity provide the mechanism for the process we know as plate tectonics. Earthquakes, volcanoes, and the earth's magnetic field are all a consequence of the earth trying to lose heat as it converts some of the thermal energy into mechanical energy in the process. Without the tremendous heat being released from the interior of the earth, we would not have had the mechanism to drive plate tectonics.
Source: https://youtu.be/UD7GHzIRI-s?t=2m18s
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| Current plate movement can be tracked directly by means of space-based geodetic measurements; geodesy is the science of the size and shape of the Earth. Because plate motions are global in scale, they are best measured by satellite-based methods. The late 1970s witnessed the rapid growth of space geodesy, a term applied to space-based techniques for taking precise, repeated measurements of carefully chosen points on the Earth’s surface separated by hundreds to thousands of kilometers. The Global Positioning System (GPS) has been the most useful for studying the Earth’s crustal movements. By repeatedly measuring distances between specific points, geologists can determine the movement along faults or between plates. The separations between GPS sites are already being measured regularly around the Pacific basin. By monitoring the interaction between the Pacific Plate and the surrounding mostly continental plates, scientists are learning more about events that build up to earthquakes and volcanic eruptions in the circum- Pacific “Ring of Fire”. Space-geodetic data have already confirmed that the rates and directions of plate movements, averaged over several years, compare well with rates and directions of plate movements averaged over millions of years. |
-- http://www.iris.edu/hq/files/programs/education_and_outreach/aotm/14/1.GPS_Background.pdf
| Scientists are able to calculate average rates of tectonic plate movement for a given time period. These rates of movement range widely. For example, the rate of spreading at the Mid-Atlantic Ridge near Iceland is relatively slow, about 2.5 centimeters (1 inch) per year...The fastest known rate of plate movement, 15 centimeters (6 inches) per year, occurs on the East Pacific Rise in the South Pacific. |
-- http://education.nationalgeographic.com/education/media/plate-tectonics/?ar_a=1
"The Indian Plate is currently moving north-east at 5 centimetres (2.0 in) per year, while the Eurasian Plate is moving north at only 2 centimetres (0.79 in) per year. This is causing the Eurasian Plate to deform, and the Indian Plate to compress at a rate of 4 millimetres (0.16 in) per year." -- http://en.wikipedia.org/wiki/Indian_Plate
See also: Unusual Indian Ocean earthquakes hint at tectonic breakup
When land masses collide, the pressure can create what geologists call “fold and thrust belts.” Slabs of sedimentary rock that were laid down horizontally can be squeezed into wavy anticlines and synclines. Sometimes the rock layers break completely, and older layers of rock pile up on top of younger layers. This type of break, known as a thrust fault, formed the series of ridges seen in the images above.
Another type of fault is visible as well. In two areas, the ridges are noticeably offset by a strike-slip or “tear” fault. The top image shows Piqiang Fault, a northwest trending strike-slip fault that runs roughly perpendicular to the thrust faults for more than 70 kilometers (40 miles). The colored sedimentary rock layers are offset by about 3 kilometers (2 miles) in this area.
-- http://earthobservatory.nasa.gov/IOTD/view.php?id=82853
As can be seen on a map of the world, the continental coastlines of North America and Europe and of South America and Africa almost match. If the edges of the continental shelves are matched, the fit is nearly perfect. Other geologic and paleontological similarities found on both sides of the Atlantic substantiate the theory of plate tectonics and thus help explain the evolution of the Atlantic.
Perhaps the most conclusive evidence bearing out this theory of origin is to be found in the existence of the Mid-Atlantic Ridge. The ridge is in effect a long rift zone of mountains, volcanoes, and faulted plateaus. A high heat flow, which is associated with the extrusion of magma and with seafloor spreading, exists in the rift zone. The crustal material on either side of the ridge is notably younger than that on the corresponding plateaus, indicating an uprising of material from Earth’s mantle onto the crest of the ridge. The newer rock is composed mainly of gabbro (a coarse-grained rock formed deep within the mantle under heat and pressure), basalt (a rock that originally poured out at the surface in molten form), and serpentine (a common rock-forming mineral). Consequent movement of the ocean floor and of the continents in opposite directions outward from the ridge is widening the Atlantic basin at an estimated rate of about 0.4 inch (1 cm) to a maximum of about 4 inches (10 cm) per year. The worldwide average rate has been estimated at 1 inch (2.5 cm) annually. Corresponding spreading is occurring at an even faster pace in the Pacific Ocean; in the Atlantic, however, the slower rate of spreading causes the flanks of the ridge to be built up steeply by accumulating lava.
-- http://www.britannica.com/place/Atlantic-Ocean#toc33282
Perhaps the most conclusive evidence bearing out this theory of origin is to be found in the existence of the Mid-Atlantic Ridge. The ridge is in effect a long rift zone of mountains, volcanoes, and faulted plateaus. A high heat flow, which is associated with the extrusion of magma and with seafloor spreading, exists in the rift zone. The crustal material on either side of the ridge is notably younger than that on the corresponding plateaus, indicating an uprising of material from Earth’s mantle onto the crest of the ridge. The newer rock is composed mainly of gabbro (a coarse-grained rock formed deep within the mantle under heat and pressure), basalt (a rock that originally poured out at the surface in molten form), and serpentine (a common rock-forming mineral). Consequent movement of the ocean floor and of the continents in opposite directions outward from the ridge is widening the Atlantic basin at an estimated rate of about 0.4 inch (1 cm) to a maximum of about 4 inches (10 cm) per year. The worldwide average rate has been estimated at 1 inch (2.5 cm) annually. Corresponding spreading is occurring at an even faster pace in the Pacific Ocean; in the Atlantic, however, the slower rate of spreading causes the flanks of the ridge to be built up steeply by accumulating lava.
-- http://www.britannica.com/place/Atlantic-Ocean#toc33282
Evidence drawn from various geophysical fields—seismology, volcanology, gravimetry, and paleomagnetism (remanent magnetism)—points to the general validity of the theory of plate tectonics. All the major physical features in the Pacific are understood to originate in plate tectonics. The western Pacific arcs of volcanic islands and deep trenches are convergent zones where two plates are colliding, one being subducted (forced under the other). The East Pacific Rise is an active spreading centre where new crust is being created. The northeastern Pacific margin is the strike-slip zone where the American Plate and the Pacific Plate are gliding laterally past each other via the major San Andreas Fault system. In the southeastern Pacific, however, the Nazca Plate and the South American Plate are colliding to form the Andes Mountains along western South America and, a short distance offshore, the Peru-Chile Trench. The floor of the northeastern Pacific is remarkable for its several major fracture zones, which extend east and west and which, in some instances, are identifiable over distances of thousands of miles.
-- http://www.britannica.com/place/Pacific-Ocean#toc36084
-- http://www.britannica.com/place/Pacific-Ocean#toc36084