Earth Planet. Ross, M. Icarus, 42, — Lunar and Planet. Ross M. Icarus, 85, — Schubert, G. Icarus, 47, 46— Burns and M. Fluid Mech. Kieffer, B. Jakosky, C. Snyder and M.
Tucson, Arizona: University of Arizona Press, pp — Segatz M. Icarus, 75, — Shearer, P. Nature, , —6. Sleep, N. Stevenson, D. Icarus, 54, — Formation and early evolution of the Earth. In Mantle Convection ed. New York: Gordon and Breach, pp. Tackley, P. Nature, , — Tozer, D. The formation of the core. Turcotte, D. Paleomagnetism is the study of magnetism in ancient rocks.
In other words, the particles will point in the direction of the magnetic field present as the rock was cooling. Seafloor spreading gradually pushes tectonic plates apart at mid-ocean ridges.
When this happens, the opposite edge of these plates push against other tectonic plates. Subduction occurs when two tectonic plates meet and one moves underneath the other Fig. Oceanic crust is primarily composed of basalt, which makes it slightly denser than continental crust, which is composed primarily of granite. Because it is denser, when oceanic crust and continental crust meet, the oceanic crust slides below the continental crust.
This collision of oceanic crust on one plate with the continental crust of a second plate can result in the formation of volcanoes Fig. As the oceanic crust enters the mantle, pressure breaks the crustal rock, heat from friction melts it, and a pool of magma develops.
This thick magma, called andesite lava, consists of a mixture of basalt from the oceanic crust and granite from the continental crust. Forced by tremendous pressure, it eventually flows along weaker crustal channels toward the surface. The magma periodically breaks through the crust to form great, violently explosive composite volcanoes —steep-sided, cone-shaped mountains like those in the Andes at the margin of the South American Plate Fig. Continental collision occurs when two plates carrying continents collide.
Because continental crusts are composed of the same low-density material, one does not sink under the other. During collision, the crust moves upward, and the crustal material folds, buckles, and breaks Fig. The Himalayan Mountains were formed by the collision between Indian and Eurasian tectonic plates. Ocean trenches are steep depressions in the seafloor formed at subduction zones where one plate moves downward beneath another Fig.
These trenches are deep up to The deepest ocean trench is the Mariana Trench just east of Guam. It is located at the subduction zone where the Pacific plate plunges underneath the edge of the Filipino plate. Subduction zones are also sites of deepwater earthquakes. Transform faults are found where two tectonic plates move past each other.
As the plates slide past one another, there is friction, and great tension can build up before slippage occurs, eventually causing shallow earthquakes. People living near the San Andreas Fault, a transfom fault in California, regularly experience such quakes. Recall that some volcanoes form near plate boundaries, particularly near subduction zones where oceanic crust moves underneath continental crust Fig.
However, some volcanoes form over hot spots in the middle of tectonic plates far away from subduction zones Fig. When magma erupts and flows at the surface, it is called lava. The basalt lava commonly found at hot spots flows like hot, thick syrup and gradually forms shield volcanoes. A shield volcano is shaped like a dome with gently sloping sides. These volcanoes are much less explosive than the composite volcanoes formed at subduction zones.
Some shield volcanoes, such as the islands in the Hawaiian archipelago, began forming on the ocean floor over a hot spot. Each shield volcano grows slowly with repeated eruptions until it reaches the surface of the water to form an island Fig. Almost all of the mid-Pacific and mid-Atlantic ocean basin islands formed in a similar fashion over volcanic hot spots. Over millions of years as the tectonic plate moves, a volcano that was over the hot spot moves away, ceases to erupt, and becomes extinct Fig.
Islands can erode through natural processes such as wind and water flow. Eventually all that remains of the island is a ring of coral reef.
An atoll is a ring-shaped coral reef or group of coral islets that has grown around the rim of an extinct submerged volcano forming a central lagoon Fig. Atoll formation is dependent on erosion of land and growth of coral reefs around the island.
Coral reef atolls can only occur in tropical regions that are optimal for coral growth. There are three main types of plate boundary. These are convergent destructive , divergent constructive and conservative.
The direction of plate movement dictates the features and processes associated with each tectonic plate boundary. Plate Margins There are three main types of plate boundary. Search for:. Pin It on Pinterest.
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